AP photographers returned to more than a dozen of those locations in recent weeks, from Portland to Cleveland and Corpus Christi, Texas. Of the 20,000 photos in the archive, the AP selected those that focused on environmental issues, rather than the more general shots of everyday life in the 1970s.

Gone are the many obvious signs of pollution — clouds of smoke billowing from industrial chimneys, raw sewage flowing into rivers, garbage strewn over beaches and roadsides — that heightened environmental awareness in the 1970s, and led to the first Earth Day and the EPA’s creation in 1970. Such environmental consciousness caused Congress to pass almost unanimously some of the country’s bedrock environmental laws in the years that followed.

Today’s pollution problems aren’t as easy to see or to photograph. Some in industry and politics question whether environmental regulation has gone too far and whether the risks are worth addressing, given their costs.

Republican presidential contender Mitt Romney has called for the firing of EPA chief Lisa Jackson, while GOP rival Newt Gingrich has said the EPA should be replaced altogether. Jackson has faced tough questioning on Capitol Hill so often the in past two years that a top Republican quipped that she needs her own parking spot.

“To a certain extent, we are a victim of our own success,” said William Ruckelshaus, who headed the EPA when it came into existence under Republican President Richard Nixon and was in charge during the Documerica project. “Right now, EPA is under sharp criticism partially because it is not as obvious to people that pollution problems exist and that we need to deal with them.”

Environmental laws that passed Congress so easily in Ruckelshaus’ day are now at the center of a partisan dispute between Republicans and Democrats. Dozens of bills have been introduced to limit environmental protections that critics say will lead to job losses and economic harm, and there are those who question what the vast majority of scientists accept — that the burning of fossil fuels is causing global warming.

In the 1970s, the first environmental regulations were just starting to take effect, with widespread support. Now, according to some officials in the oil and gas and electric utility industries, which are responsible for the bulk of emissions and would bear the greatest costs, the EPA has gone overboard with rules.

For instance, Documerica photographers captured a wave of coal-fired power plants under construction. Republicans and the industry now say environmental regulations are partly to blame for shuttering some of the oldest and dirtiest coal plants.

Jim DiPeso of ConservAmerica, a group that recently changed its name from Republicans for Environmental Protection, says the EPA is caught in the center of a perfect storm. “This time of greater cynicism about government, more economic anxiety and the fact that the problems are not immediately apparent, has created this political problem for EPA,” he said.

In an interview, Jackson said she believes that people in the United States still want to protect the environment. “There’s a large gulf between the rhetoric inside the Beltway to do everything from cut back on EPA to get rid of the whole place, and what the American people would actually stand for,” she said. “It’s very easy to make rash statements without thinking about what that means to the health of everyday Americans.”

A 2010 Pew Research Center survey showed that 57 percent of those questioned held a favorable view of the EPA, compared with a 1997 poll that showed 69 percent with a positive view of the agency. A CNN/Opinion Research Corp. poll taken last year found that 71 percent of people surveyed said that the government should continue provide money to the EPA to enforce regulations to address global warming and other environmental issues.

“We are not done. We still have challenges we have to face,” Jackson said.

The agency last year began a volunteer photography project called State of the Environment. More than 620 people have participated and submitted 1,800 photographs, but only a few are at the same sites at the 1970s project.

Images always have spurred environmental consciousness. A 1980s satellite picture of the ozone hole helped lead to a ban on the chemicals in aerosol cans and refrigerants that were responsible. Underwater video of oil spewing into the Gulf of Mexico in 2010 opened the public’s eyes to the gravity of the largest offshore oil spill in U.S. history.

But a second Documerica project, with professional photographers, would be impossible today, given budget cuts facing the agency and the wariness of industry barring access by photographers.

Lyntha Scott Eiler, 65, shot photographs for Documerica around her then-home in northern Arizona, as well as one of the early emissions testing sites for automobile exhaust in Hamilton County, Ohio. At the Navajo Generating Station in Arizona, Eiler got right down in a strip mine “where the shovels were.”

“They weren’t afraid of the EPA, so it was, ‘What else you do you want to get a photograph of?,’” Eiler said. “You probably would have a hard time doing that today.”

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For Obama, the announcement provides an answer to Republicans who say his energy policies, including the rejection of the larger Canada-Texas pipeline, have contributed to high gas prices and destroyed jobs.

The longer 1,700-mile pipeline became a political flashpoint late last year when congressional Republicans wrote a provision forcing Obama to make a decision, and environmental groups waged a campaign to kill the project. In January, Obama delayed it, saying the deadline didn’t leave enough time for review.

The issue has become a central focus in the heated political fight over energy development in the 2012 election.

Calgary-based TransCanada hopes to complete the $2.3 billion Oklahoma-to-Texas section next year after receiving the last approvals it needs to start construction. Many of the permits and environmental reviews already have been completed as part of the larger Keystone project, company officials said.

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Cappiello reported from Washington.

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Follow Dina Cappiello’s environment coverage on Twitter (at)dinacappiello

The measure cleared the Senate 76-22 as part of a larger transportation bill. Gulf Coast politicians lobbied hard to get the funds.

“This bipartisan legislation directs support to the Gulf States where it is needed,” said U.S. Sen. Roger Wicker, R-Miss.

Environmental groups called the vote a major victory.

“When was the last time we had 76 votes in the Senate, let alone 76 votes on a bill to invest billions in restoring one of America’s most treasured landscapes?” said Paul Harrison of the Environmental Defense Fund.

Earlier this year, the House passed a similar measure to divert the money. President Barack Obama has also called for disbursing the penalties to the states.

It is uncertain when BP will be forced to pay the fines. It is possible that the Justice Department and BP could settle the case before it goes to trial or the fines could be assessed after a trial.

Under the measure, the money would be spent on projects to restore the environment and the Gulf Coast’s economy. A portion of the money also would go into a science fund to study the Gulf.

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Associated Press writer Cain Burdeau contributed to this report from New Orleans.