The White House predicted Wednesday that the US Senate will ratify a landmark nuclear treaty with Russia this year despite stiff Republican objections that have clouded the agreement's fate.

The new Strategic Arms Reduction Treaty (START) "will come up and I think the treaty will be voted on. And I think we'll have enough votes to pass it," spokesman Robert Gibbs told reporters.

But it was far from clear that eight Republicans would side with Democrats to give the treaty the 67 votes needed for ratification in the 100-seat chamber and hand President Barack Obama a major foreign policy victory.

The number needed rises to 14 in January when a new Congress, fruit of November 2 elections in which Republicans routed Democrats, takes office.

Gibbs's comments came hours after US Secretary of State Hillary Clinton pressed the US Senate to vote in the year-end "lame-duck" session on the pact, calling it vital to US national security and "critical" to ties with Moscow.

"We can, and we must, go forward now on the new START treaty during the lame-duck session" now under way, she said during a rare public appearance with key lawmakers in the US Capitol. "This treaty is ready to be voted on."

Clinton vowed to "continue and intensify" talks with Republicans and work "literally around the clock" to address any lingering good-faith objections.

The START treaty -- signed by Russian President Dmitry Medvedev and Obama in Prague in April -- restricts each nation to a maximum of 1,550 deployed warheads, a cut of about 30 percent from a limit set in 2002.

It would also return US inspectors who have been unable to monitor Russia's arsenal since the agreement's predecessor lapsed in December 2009.

Republicans repeatedly delayed action on the treaty over the past year and signaled Tuesday they would block a vote until 2011 -- dealing Obama a stinging defeat, who has made approval this year a top goal.

Number-two Republican Senator Jon Kyl said Tuesday he opposed a vote because of "complex and unresolved issues" about "modernization" of the US nuclear arsenal -- ensuring that the US deterrent remains credible.

In response to Kyl's concerns, the White House weeks ago added 4.1 billion dollars over five years to its 10-year budget of 80 billion dollars for that purpose.

Other Republicans want iron-clad assurances the pact will not hamper US missile defense plans fiercely opposed by Russia, citing a unilateral statement from Moscow that moves on that front risked voiding the treaty.

In a show of impatience with Kyl, Clinton criticized lawmakers who "have suggested we should hit the pause button, that it is too difficult to do this treaty in a lame-duck session.

"This is exactly what the American people expect us to do, to come together and do what is necessary to protect our country," she said, flanked by Democratic Senator John Kerry and Republican Senator Richard Lugar, the chairman and ranking member of the Senate Foreign Relations Committee.

Clinton noted that Russia's lower house of parliament, the Duma, awaited US ratification to launch its own process of approving the accord.

Democratic Senate Majority Leader Harry Reid said in a statement he was "puzzled" by Kyl's objection to the treaty and declared lawmakers "will have time to consider and ratify it" in December.

Lugar, a lifelong champion of arms control efforts and supporter of the treaty, sternly upbraided his fellow Republicans and warned against an "inexcusable" delay.

"We're at a point where we're unlikely to have either the treaty or modernization unless we get real," he said.

Lugar expressed disbelief that lawmakers would be "deeply concerned about North Korea and Iran" while forgetting that Moscow still possessed "thousands" of warheads trained on US targets.

"As of now, there is no substantive disagreement on this treaty," said Kerry, who pleaded with colleagues to "leave politics at the water's edge."