Despite skepticism from Republican opponents who worry that the U.S. is deliberately fraying its nuclear advantage, the Obama administration considers a new arms control pact with Russia a disarmament bargain.

The agreement is more important for the diplomatic bargain it seals with a restive Russia than the limits it places on weapons that neither side was likely to use — treaty or no treaty.

It will probably also help cinch Russian cooperation with an American plan to protect Europe with an anti-missile shield arrayed against Iran.

Presidents Barack Obama and Dmitry Medvedev congratulated one another by phone Thursday, the White House said. The two leaders called the agreement historic and the capstone for a "very productive year" of cooperation on issues including Iran sanctions and the war in Afghanistan.

Medvedev already had welcomed the U.S. Senate's decision to ratify the landmark nuclear arms control treaty, while Russian legislators said they need to study a resolution accompanying the document before following suit.

The Senate voted 71-26 on Wednesday to ratify the treaty, a clear victory for the White House after weeks in which it seemed doubtful that President Barack Obama could muster enough Republican votes. Obama had called approval of the treaty his highest foreign policy priority this year.

"This is the most significant arms control agreement in nearly two decades," Obama said shortly after the Senate approved the deal. He asserted that the treaty "will make us safer" and allow U.S. inspectors to return to Russian nuclear bases.

"We'll continue to advance our relationship with Russia, which is essential to making progress on a host of challenges," Obama added.

The pact, called New START, is the centerpiece of a mutual U.S.-Russian effort to repair relations badly damaged during the latter years of the George W. Bush administration.

Obama and Medvedev signed the treaty in April with bonhomie intended to show that the pact was about making things right with Moscow as well as reducing warheads. Russian leaders let it be known they considered the treaty a test of Obama's sincerity and clout.

The New START treaty replaces the expired Strategic Arms Reduction Treaty of 1991. It sets a limit of 1,550 strategic nuclear warheads for each side, down from 2,200 under a 2002 deal. The pact also re-establishes anti-cheating procedures that were not written into the 2002 accord, thus making it the most comprehensive and substantial arms control pact since the 1991 treaty.

But that ambitious nuclear downscaling was jeopardized when Obama won NATO support in November to build a missile shield over Europe. The commitment to erect the shield, ostensibly aimed at Iran, remained one of the major irritants with Russia until Obama scrapped plans to stage parts of it at Russia's doorstep.

His reworked missile shield plan got a polite but noncommittal reception from Moscow, and Obama's advisers breathed a cautious sigh of relief. A public fight with Russia over missile defense might have sunk the new treaty with just weeks to go before the close of the current congressional session.

With Senate approval, the administration can fully exhale. Carrying the treaty over into 2011 would have made it harder to pass, and rubbed salt in already-sensitive Russian irritation at the slow pace of U.S. approval and at Republican suggestions that parts of the treaty might have to be reworked.

Following the Senate vote Wednesday, the Russians also seemed to breathe easier.

"The treaty represents a shift away from the Cold War mentality and demonstrates that Russia and the U.S. are focused on achieving 21st century global security," said Sen. Mikhail Margelov, head of Russia's Committee for Foreign Affairs.

Boris Gryzlov, lower house speaker of Russia's parliament, said it could ratify the treaty as soon as Friday — once Russian lawmakers have time to study the ratification resolution that accompanied the Senate vote.

The Obama administration took office pledging to start fresh with Moscow, which had been at odds with Washington on all but a handful of foreign policy priorities after a period of post-Cold War partnership and goodwill.

Moscow resented what Russians saw as in-your-face behavior by the U.S. — on the touchy issue of U.S. missiles based near Russia, on U.S. backing for anti-Russian political movements in former Soviet states and on the invasion of Iraq, once a Soviet partner.

Russia struggled to cope with its loss of superpower status, and nursed a grudge.

Obama hoped, rightly, that the expiring arms control treaty could provide footing for cooperation with Russia. The two nations worked together to draft the follow-up pact, and predicted that once ratified it might be a springboard to other partnerships.

That's where things started to go wrong.

Republican dissent spread during the spring and summer, as Obama's political fortunes sank and his administration struggled to answer criticism of the treaty.

Opponents claimed the pact would limit U.S. options for future missile defense systems. There were concerns as well about the largely untested proposition that incoming enemy missiles could be detected and shot down by defensive equipment placed in key spots in Europe and the Persian Gulf region.

Iran is the obvious boogeyman, but there are plans for missile-based defense systems against threats that might come from North Korea or other potential aggressors.

In fact, New START places no practical constraints on missile defense, but the administration was slow to make its argument forcefully and back it with endorsements from former GOP Cabinet and security bigwigs.

New START is also meant as an example to other nations that might want to build up arsenals or resist U.S. entreaties to reduce existing stockpiles. Although the treaty leaves both the United States and Russia with plenty of firepower to annihilate one another, the large reductions it imposes are supposed to bolster U.S. credibility when it argues that the world should work toward the eradication of nuclear weapons.

The passing of the Cold War, the rise of radical Islamic extremism and the emergence of sophisticated terrorist networks have changed the nuclear equation.

Still, Senate opponents, led by Republican Sen. Jon Kyl of Arizona, wanted assurances that the remaining nuclear arsenal is modernized and effective.

The administration pledged $85 billion to maintain the nuclear arsenal over the next 10 years, including a $4.1 billion boost recently, in an attempt to address Kyl's concerns.

Obama and Senate Democrats backing the treaty claimed that getting inspectors back on the ground in Russia is so urgent that the U.S. could not afford to put off a vote on the treaty to next year.

That blurred the real reason Obama wanted to move now: He faces a larger Republican minority in the Senate when the new Congress takes over in January and any GOP effort to alter the pact would anger Russia and make Obama look less trustworthy in Russian eyes.


EDITOR'S NOTE: Anne Gearan covers U.S. foreign policy and national security in Washington for The Associated Press.