The Senate has voted to close out debate on a new arms control treaty with Russia, setting the stage for ratification of the accord.
The vote was 67-28 and was seen in part as a proxy vote for the final tally. President Barack Obama considers the treaty his top foreign policy priority in the postelection Congress.
Almost a dozen Republicans joined all the Democrats in calling for an end to the debate. Vice President Joe Biden and Secretary of State Hillary Rodham Clinton were at the Capitol lobbying lawmakers.
Earlier in the day, Obama locked up the votes for ratification of the treaty as at least 10 Republicans said they would back the accord. A final vote is likely on Wednesday.
THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.
WASHINGTON (AP) -- President Barack Obama locked up enough Republican votes on Tuesday to secure Senate ratification of a new arms control treaty with Russia that would give him a foreign policy victory to top his postelection political wins.
Lamar Alexander of Tennessee, the No. 3 Republican in the Senate, endorsed the accord that would cap nuclear warheads for both countries and resume on-site weapons inspections. The accord will leave the United States "with enough nuclear warheads to blow any attacker to kingdom come," Alexander said on the Senate floor, adding, "I'm convinced that Americans are safer and more secure with the New START treaty that without it."
Alexander's announcement accelerated momentum for the treaty that the United States considers a centerpiece in resetting the relationship between the former Cold War foes.
Four other Republican senators -- Lisa Murkowski of Alaska, Johnny Isakson of Georgia, Bob Corker of Tennessee and Robert Bennett of Utah -- said they would back the pact that under the Constitution requires two-thirds of those voting in the Senate to ratify.
Democrats had at least 10 Republican votes for the treaty, overcoming the fierce opposition of the Senate's top two GOP leaders -- Minority Leader Mitch McConnell of Kentucky and Jon Kyl of Arizona, the Republican point man on the pact.
The Senate scheduled a vote Tuesday afternoon to cut off debate on the pact, and a final vote was likely on Wednesday.
"We know when we've been beaten," Republican Sen. Orrin Hatch of Utah told reporters.
Obama has insisted the treaty is a national security imperative that will improve cooperation with Russia, an argument loudly echoed by the nation's military and foreign policy leaders, former Presidents George H.W. Bush and Bill Clinton and six Republican secretaries of state.
In a fresh appeal for ratification, Defense Secretary Robert Gates said Tuesday that the treaty would "strengthen our leadership role in stopping the proliferation of nuclear weapons, and provide the necessary flexibility to structure our strategic nuclear forces to best meet national security interests."
Conservative foes of the accord -- among them possible GOP presidential candidates Mitt Romney, Sarah Palin, Newt Gingrich and Tim Pawlenty -- argue the treaty would restrict U.S. options on a missile defense system to protect America and its allies and lacks sufficient procedures to verify Russia's adherence.
That opposition withered in the face of forceful statements from the military establishment, including Joint Chiefs of Staff Chairman Adm. Mike Mullen who said Monday that the treaty "enhances our ability to do that which we in the military have been charged to do: protect and defend the citizens of the United States."
Obama, who postponed his holiday vacation, lobbied hard for the Senate to complete the treaty before January when Republicans increase their numbers by five and the accord's outlook would be bleak. Vice President Joe Biden and Secretary of State Hillary Rodham Clinton, who have made numerous calls to senators, paid personal visits to the Senate on Tuesday.
Weeks after Republicans routed Democrats at the polls -- seizing control of the House and strengthening their numbers in the Senate -- Obama has prevailed in securing overwhelming bipartisan approval of a tax deal with Republicans and getting repeal of the 17-year-old ban on openly gay military members, a crucial issue with the party's liberal base.
The White House had made steady progress in its efforts to persuade Republican lawmakers despite McConnell and Kyl's opposition.
In announcing his support, Alexander said he was reassured by a letter from Obama, in which the president reiterated his commitment to modernizing the remaining nuclear arsenal with projected spending of $85 billion over 10 years. A significant amount of that money would go to nuclear facilities at Los Alamos, N.M., and Oak Ridge, Tenn., a critical issue with Alexander and Corker.
"My administration will pursue these programs and capabilities for as long as I am president," Obama wrote in letters to Republican Sens. Alexander and Thad Cochran and Democrats Dianne Feinstein and Daniel Inouye.
Republicans and Democrats were discussing amendments to the accompanying resolution, not the treaty, that would deal with Republican problems with missile defense and build support for the agreement.
The treaty specifically would limit each country's strategic nuclear warheads to 1,550, down from the current ceiling of 2,200. It also would establish a system for monitoring and verification. U.S. weapons inspections ended a year ago with the expiration of a 1991 treaty.
All 57 members of the Democratic caucus are expected to back the treaty; Sen. Ron Wyden, D-Ore., underwent cancer surgery on Monday and is likely to miss the vote. Republicans who have announced they will vote for the treaty are Richard Lugar of Indiana, Olympia Snowe and Susan Collins of Maine, Scott Brown of Massachusetts and George Voinovich of Ohio.
"I think it's going to pass and more than just pass," Corker told reporters.
Announcing they would oppose the treaty were Hatch and Sen. Lindsey Graham of South Carolina, two Republicans facing re-election in 2012 and possible primary challenges from tea party-backed candidates.