The issue now goes to the House, which has yet to consider a separate version of the bill.

“The Postal Service is an iconic American institution that still delivers 500 million pieces of mail a day and sustains 8 million jobs,” said Sen. Joe Lieberman, I-Conn., a bill co-sponsor. “This legislation will change the USPS so it can stay alive throughout the 21st century.”

The mail agency, however, criticized the measure, saying it fell far short in stemming financial losses. Postmaster General Patrick Donahoe said if the bill became law, he would have to return to Congress in a few years to get emergency help.

“It is totally inappropriate in these economic times to keep unneeded facilities open. There is simply not enough mail in our system today,” the Postal Service’s board of governors said in a statement. “It is also inappropriate to delay the implementation of five-day delivery.”

The Senate bill would halt the immediate closing of up to 252 mail-processing centers and 3,700 post offices, part of a postal cost-cutting plan to save some $6.5 billion a year. Donahoe previously said he would begin making cuts after May 15 if Congress didn’t act, warning that the agency could run out of money this fall.

The measure would save about half the mail processing centers the Postal Service wants to close, from 252 to 125, allowing more areas to maintain overnight first-class mail delivery for at least three more years. It also would bar any shutdowns before the November elections, protect rural post offices for at least a year, give affected communities new avenues to appeal closing decisions and forbid cuts to Saturday delivery for two years.

At the same time, the Postal Service would get an infusion of roughly $11 billion, basically a refund of overpayments made in previous years to a federal retirement fund. That would give it immediate liquidity to pay down debt to forestall bankruptcy and finance buyouts to 100,000 postal employees.

The agency could make smaller annual payments into a future retiree health benefits account, gain flexibility in trimming worker compensation benefits and find additional ways to raise postal revenue under a new chief innovation officer.

Other bill provisions would:

—Place a one-year moratorium on closing rural post offices and then require the mail agency to take rural issues into special consideration. Post offices generally would be protected from closure if the closest mail facility was more than 10 miles away. The exception would be cases in which there was no significant community opposition.

—Shut five of the seven post offices on the Capitol grounds.

—Take into account the impact on small businesses before closing mail facilities.

—Cap postal executive pay through 2015 at $199,000, the same level as a Cabinet secretary, and create a system under which the top people at the Postal Service are paid based on performance.

The Senate bill faces an uncertain future. The House version, approved in committee last year, would create a national commission with the power to scrap no-layoff clauses in employee contracts and make other wide-ranging cuts.

“This of course kicks the can down the road,” complained Sen. John McCain, R-Ariz., who unsuccessfully pushed for a commission in the Senate bill. He said the current proposal failed to address longer-term fixes and delayed major decisions. “We’ll be on the floor in two years addressing this issue again, because it is not a solution.”

Noting that more people every year are switching to the Internet to send letters and pay bills, Donahoe called the Postal Service’s business model “broken.” The agency has estimated that the Senate bill would only provide it enough liquidity to continue operating for two years or three years.

At stake are more than 100,000 jobs, The agency, $12 billion in debt, says it could run out of money for day-to-day operations as soon as this fall, forcing it to shut down some of its services. The mail agency forecasts a record $14.1 billion loss by the end of this year; without changes, it says annual losses will exceed $21 billion by 2016.

On Tuesday, the Postal Service circulated a smaller list of mail processing centers that probably would close under the Senate bill; many in more rural or small states would be spared. For instance, centers would survive in Connecticut, Delaware, Maine, Missouri and Vermont, whose senators were sponsors of the postal bill or pushed amendments, according to the preliminary list obtained by The Associated Press. A facility in Easton, Md., also would stay open. Sen. Barbara Mikulski, D-Md., previously attempted to block the postal bill in protest of that specific closure.

Also surviving were all four mail processing centers in Nevada, home to Senate Majority Leader Harry Reid, as well as all eight centers in Colorado and all five centers in Utah.

“This bill is a vital first step in pulling the Postal Service back from the edge of a fiscal abyss,” said Art Sackler, coordinator of the Coalition for a 21st Century Postal Service, a group representing the private sector mailing industry.

“It’s now critical that the House follow suit quickly or we risk a shutdown of the Postal Service and an ensuing economic calamity,” he said.

The Postal Service, an independent agency of government, does not receive taxpayer money for its operations but is subject to congressional control.

The Senate was scheduled to vote as early as Wednesday on a final bill, after first considering amendments that in part could restrict the Postal Service from further cuts to first-class mail delivery. On Tuesday, senators agreed to tack on amendments that would bar the shuttering of rural post offices for a year, give afflicted communities new avenues of appeal and prevent any closings before the November elections.

The final bill was expected to pass the Senate but faces an uncertain future. The House has yet to begin consideration of a different version of a postal bill, which seeks to create a national commission that would make major decisions on postal cuts and make it easier to eliminate Saturday delivery. The commission, which would have authority to do away with no-layoff clauses in postal employee contracts, is fiercely opposed by postal unions.

“This of course kicks the can down the road,” complained Sen. John McCain, R-Ariz., who unsuccessfully pushed for a commission in the Senate bill. He argued that the current bill failed to address longer-term fixes, instead hiding behind studies and reviews that unnecessarily delayed major decisions. “We’ll be on the floor in two years addressing this issue again, because it is not a solution.”

Postmaster General Patrick Donahoe also has criticized the Senate bill as a short-term answer. Noting that more people every year are switching to the Internet to send letters and pay bills, he has called the Postal Service’s business model “broken.” The agency has estimated that the Senate bill would only provide it enough liquidity to continue operating for two or three years.

At stake are more than 100,000 jobs, part of a postal cost-cutting plan to save some $6.5 billion a year by closing up to 252 mail-processing centers and 3,700 post offices. The mail agency, which is already $12 billion in debt, says it needs to begin closings this year. At the request of Congress, Donahoe agreed to delay closings until May 15 to give lawmakers time to pass legislation.

The Senate bill seeks to cut about half the number of mail processing centers the Postal Services currently wants to close — from 252 to 125 — allowing more U.S. areas to maintain overnight first-class mail delivery for at least three more years. Beyond the one-year moratorium on closing rural post offices, the Postal Service would be required to undergo additional layers of approval before closing any mail facility.

In the meantime, the Postal Service would get a cash infusion of roughly $11 billion, basically a refund of overpayments it made in previous years to a federal retirement fund; the agency could use the money to pay down debt and offer buyouts to 100,000 postal employees. It would be allowed to make smaller annual payments into a future retiree health benefits account, which currently amounts to more than $5 billion a year, get more flexibility to cut worker compensation benefits and be required to establish a chief innovation officer to find new ways to bring in postal revenue.

Under an amendment passed Tuesday, the Postal Service would be specifically barred from closing post offices for one year if they are located in rural areas — those with fewer than 50,000 people. The exception would be if there was no significant community opposition.

After one year, the mail agency would have to take rural issues into special consideration, including economic impact, the quality of Internet broadband service and location. Post offices would generally be shielded from closing if the next closest mail facility was more than 10 miles away.

“Our post offices are the lifeblood for towns across our state and a source of good-paying jobs in areas hard-hit by the economic downturn,” said Claire McCaskill, D-Mo., who co-sponsored the amendment. “This amendment protects rural post offices, with a realistic eye toward the future.”

Roughly 6.1 million unauthorized Mexican immigrants were living in the U.S. last year, down from a peak of nearly 7 million in 2007, according to the Pew Hispanic Center study released Monday. It was the biggest sustained drop in modern history, believed to be surpassed in scale only by losses in the Mexican-born U.S. population during the Great Depression.

Much of the drop in illegal immigrants is due to the persistently weak U.S. economy, which has shrunk construction and service-sector jobs attractive to Mexican workers following the housing bust. But increased deportations, heightened U.S. patrols and violence along the border also have played a role, as well as demographic changes, such as Mexico’s declining birth rate.

In all, the Mexican-born population in the U.S. last year — legal and illegal — fell to 12 million, marking an end to an immigration boom dating back to the 1970s, when foreign-born residents from Mexico stood at 760,000. The 2007 peak was 12.6 million.

Christian Ballesteros, who has been at a shelter for immigrants in Matamoros, Mexico, across the border from Brownsville, Texas, pointed to stiffer U.S. penalties for repeat offenders as well as brutal criminal groups that control the Mexican side of the border as reasons for the immigration decline. Ballesteros, who has been deported four times, was recently caught after hopping the border fence near Nogales, Arizona.

“The Mexican cartels are taking over, are actually being like the border patrols on this side,” Ballesteros said. “They threaten them, ‘if you don’t pay, what we’re going to do is we’re going to cut your head off.’ That’s the worst, the worst, the worst part,” Ballesteros said.

After his last apprehension by U.S. authorities, Ballesteros was sent to a detention facility in Las Vegas for 2½ months. He fears it could be six months if he’s caught again. “You can lose money, but if you lose time there’s no way you can recover that time,” Ballesteros said, noting that many immigrants have families to support.

Jeffrey Passel, a senior demographer at Pew who co-wrote the analysis, said Mexican immigration may never return to its height during the mid-decade housing and construction boom, even with the U.S. economy recovering. He cited longer-term factors such as a shrinking Mexican work force.

He noted that government data now show a clear shift among Mexican workers already in the U.S. who are returning home. He said that data is a sign that many immigrants are giving up on life in the U.S., feeling squeezed by increasing enforcement and limited opportunities that they don’t see improving anytime soon.

About 1.4 million Mexicans left the U.S. between 2005 and 2010, double the number who did so a decade earlier. In the meantime, the number of Mexicans who entered the U.S. sharply fell to about 1.4 million, putting net migration from Mexico at a standstill. More recent data suggest that most of the movement is now heading back to Mexico, accounting for the drop in the illegal immigrant population.

During the same period, the population of authorized Mexican immigrants edged higher, from 5.6 million to 5.8 million.

Among the Mexican immigrants who leave the U.S., an estimated 5 to 35 percent are deported while the rest opt to go back voluntarily, often taking U.S.-born children with them. Those who were in the U.S. illegally and returned to Mexico also are increasingly saying they will not try to come back — about 20 percent, compared to 7 percent in 2005.

The Pew estimates come amid heightened attention on immigration in an election year where the fast-growing Hispanic population, now making up roughly 16 percent of the U.S. population, could play a key role. Arizona’s law, being challenged by the Obama administration in the Supreme Court, seeks to expand the authority of state police to ask about the immigration status of anybody they stop on the rationale that federal enforcement has largely failed.

Since Arizona’s law passed in 2010, five other states — Alabama, Georgia, Indiana, South Carolina and Utah — have passed similar measures.

Steve A. Camarota, director of research at the Center for Immigration Studies, a Washington group that advocates tighter immigration policies, said the latest numbers show that immigration policies do make a difference.

“The bottom line is that immigration is not the weather. It is something that … can be changed,” he said. “The economy is worse but enforcement is also higher, making it more difficult for immigrants to get jobs in states like Arizona. They are now making new calculations and changing their views.”

Other findings:

—Illegal Mexican immigrants who have stayed in the U.S. for longer periods of time are now more likely to be sent back by authorities than before. About 27 percent of immigrants sent back had resided in the U.S. for a year or more, up from 6 percent in 2005.

—Despite an increase in Border Patrol agents, apprehensions of illegal immigrants at the U.S.-Mexico border have dropped sharply — from 1 million in 2005 to 286,000 in 2011, a sign that fewer illegal immigrants are trying to enter.

—Some 29 percent of all current U.S. immigrants are Mexican born, by far the most from any single country; that’s down from its peak of 32 percent in 2004-2009. The next largest share comes from India, accounting for 4.5 percent of the nation’s 40 million foreign-born residents.

—A typical Mexican woman is projected to have an average of 2.4 children in her lifetime, compared with 7.3 children in 1960.

—By region, Mexican-born immigrants in the U.S. are mostly likely found in the West (51 percent) and South (33 percent). About 58 percent now live in California and Texas, down from 63 percent in 2000 as immigrants spread out over the past decade in search of jobs in other states.

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Associated Press writer Christopher Sherman in McAllen, Texas, contributed to this report.

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Online:

http://www.pewhispanic.org/