WASHINGTON - The US Senate voted on Wednesday to ratify a nuclear arms treaty with Russia, delivering President Barack Obama his top foreign policy goal as the lame-duck Congress session draws to an end.

The victory came by a margin of 71-26 in the 100-member chamber, more than the two-thirds of majority of votes needed.

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Hours before the Senate passed the new Strategic Arms Reduction Treaty (START), White House spokesman Robert Gibbs told reporters that the pact's obituary "has been written more times than I could care to remember. None of that was easy and none of what has to happen going forward is easy."

"The Senate's action today was imperative for national security, " said Richard Burt, a chief negotiator on the original START treaty, in a statement. "The new START treaty will continue the important process of reducing and monitoring US and Russian Cold War arsenals, and pave the way for the critical next step -- bringing all nuclear weapons countries into multilateral nuclear arms negotiations for the first time in history."

The Obama administration envisages the accord as the first step in a continuing process of reducing nuclear weapons, 90 percent of them are owned by the US and Russia. Russian President Dmitry Medvedev has agreed in principle to work toward further cuts.

Obama also sees the treaty as the centerpiece of his efforts to reset relations with Russia, and has delayed his holiday vacation to guide it through before the Congress breaks for holidays.

To line up support at home since the post-election Congress opened in mid-November, the president had met with heavyweights from the military and foreign communities, used his weekly address to appeal to the public, and written and made calls to like-minded yet wavering Republican senators.

He stressed the treaty as a national security imperative and warned that failure to pass would harm warming relations with Russia, citing Russia's cooperation on issues like Iran's nuclear program and the Afghanistan war. He also reminded that the treaty had gone through 18 hearings after it was sent to the Senate floor in May, with nearly 1,000 questions having been asked and answered.

He also used the venue of Nov. 19-20 NATO summit in Lisbon, Portugal to drum up broad support from allies.

Vice President Joe Biden, Secretary of State Hillary Rodham Clinton, Defense Secretary Robert Gates and Chairman of the Joint Chiefs of Staff Mike Mullen all played their part in soliciting votes.

Six former Republican secretaries of state and former Presidents George H.W. Bush and Bill Clinton, among others, threw their weight behind the treaty signed by Obama in April with Medvedev, which caps the deployed nuclear warheads in each state to no more than 1,550 over seven years, a cut of 30 percent over the current ceiling of 2,200 set in 2002, limits the number of deployed ballistic missiles and nuclear bombers to no more than 700 each, and sets up a mechanism for verification and inspection.

Opponents alleged that the treaty offers too many concessions to Russia, weakens US ability to employ missile defense technology and has insufficient procedures to verify Russia's adherence.

Since debate began last Wednesday, some Republicans have sought to defeat the treaty with delay and "treaty-killer" amendments to the preamble or text by filing more than seventy amendments. But the Democrats garnered 11 Republican votes on Tuesday to end debate and bring full vote on the treaty.

If delayed until early January when the new Congress opens, the pact is sure to face a dim outlook in the Senate as the Democrats' strength there is reduced from 58-42 to 53-47.

Russian Foreign Minister Sergey Lavrov told the Interfax news agency on Monday that ratification of the arms pact would "give a powerful impulse" to Russia-US ties.

The Russian lower house of parliament, the State Duma, said it may follow suit before the end of the year if the treaty is passed in Washington.

"The treaty will strengthen US-Russia relations, which is essential for our efforts to prevent Iran from getting the bomb and to build a strong international coalition to stop nuclear proliferation worldwide," Burt said in his statement.