Updated

As the U.S. Senate inches toward a vote on a pivotal arms treaty with Russia, officials and lawmakers in Moscow are anxiously awaiting the outcome of a debate that may shape U.S.-Russian ties for years ahead.

The Senate's failure to ratify the New START treaty would deal a harsh blow to the still fragile rapprochement between Moscow and Washington and could push the Kremlin to challenge U.S. interests across the globe.

A rejection of the pact could also weaken global stability by making the U.S. and Russia, which between them own more than 90 percent of the world's nuclear weapons, unable to check and verify the status of each other's arsenals.

"The treaty contains control procedures, and if it fails, the already low level of trust will sink further," Fyodor Lukyanov, the editor of Russia in Global Affairs magazine, told The Associated Press.

A rejection, however, seemed unlikely Tuesday as nine Republican Senators vowed to vote in favor of ratification, virtually assuring it will pass.

The new START, signed by President Barack Obama and Russian President Dmitry Medvedev in Prague in April, would reduce strategic nuclear warheads to 1,550 for each country from the current ceiling of 2,200 and re-establish inspections of missile bases and other verification measures that ceased when the previous START treaty expired nearly a year ago.

The Kremlin has pledged to synchronize Russia's ratification procedures with the U.S. Senate vote, and a top Russian lawmaker said parliament was ready to act.

Andrei Klimov, a deputy head of the foreign affairs committee in the State Duma, said lawmakers were closely watching developments in Washington and would move quickly to ratify it if the U.S. Senate gives its approval. "We will act in a gentlemanly way in keeping with our promises," he said.

But if Washington tries to amend the text of the treaty, the Duma will have to review its previous decision to support the pact and would likely make changes of its own, Klimov warned.

Russia's leaders have kept a poker face during the Senate debate to avoid being accused of meddling in U.S. politics.

But both Medvedev and Prime Minister Vladimir Putin have raised the specter of a new nuclear arms race if a separate plan for Russia and NATO to jointly build a missile defense system fails to win approval.

Russia has viewed unilateral U.S. missile defense plans as a potential threat to its security. While the New START doesn't prevent the U.S. from building new missile defense systems, as Republican critics claim, Russia has stated that it could withdraw from the treaty if it feels threatened by such a system in future.

"If the treaty fails to pass, it will not be the end of life, but it will raise a hard question for Russia of whether it makes sense to do anything together with the current U.S. administration if it is unable to see the agreements through," Lukyanov said.

If the U.S. Senate rejects the arms pact, analysts say it would likely prompt Moscow to become less cooperative on Iran and Afghanistan.

"Medvedev wouldn't be able to just sit back and pretend that nothing happened," said Viktor Kremenyuk, a deputy head of the U.S.A. and Canada Institute, a Moscow think tank that advises the Kremlin. "Agreements on Iran and Afghanistan could be reviewed."

In June, Russia joined the U.S. and others in backing the latest round of sanctions against Iran over its uranium enrichment program, which the West suspects of being a cover for a nuclear weapons bid. In another move to meet U.S. concerns, Medvedev shelved a deal to provide Iran with sophisticated S-300 air defense missiles.

The Kremlin also has offered greater assistance to the U.S.-led campaign in Afghanistan, allowing the U.S. and its NATO allies to ferry supplies across its territory as routes via Pakistan have become increasingly unsafe — a policy that also may be reviewed if the arms pact fails to get the support of the U.S. Senate.

Asked whether Moscow could rethink its support for the U.S. in Iran and Afghanistan, Foreign Minister Sergey Lavrov told the Interfax news agency this week that Russia won't engage in such "cynical give and take." But he said ratification of the arms pact would "give a powerful impulse" to bilateral ties.