In the current Senate, at least eight Republicans would have to join the Democratic bloc of 59 votes for ratification.
"I'm confident that we should be able to get the votes," Obama said.
Senate Majority Leader Harry Reid, D-Nev., sounded not quite as upbeat, telling reporters: "We're going to do our best to get a vote on the START treaty."
Once the newly elected Senate is seated in January, Democrats will need the support of at least 14 Republicans.
Suggesting how difficult that would be, 10 of the newly elected Republican senators said Thursday they supported Kyl's call for delay. In a statement, they said the nuclear pact "would dramatically reduce the U.S. nuclear deterrent."
Still, the White House sees an achievable task in winning over Republicans on grounds of national security. It has already promised a sweetener of more than $4 billion over five years to modernize America's nuclear arsenal, a promise aimed particularly to win Kyl's support.
Senate Foreign Relations Committee Chairman John Kerry, D-Mass., met on Thursday with Kyl, the GOP point man on the treaty, and several other Republican senators whose votes would be critical to ratification, including Bob Corker of Tennessee, Roger Wicker of Mississippi and John Thune of South Dakota. "Continued discussions are always helpful," said John McCain of Arizona, top Republican on the Armed Services Committee, who attended the meeting.
Thune said he didn't think the Senate should vote on the treaty before the end of the year. "There are too many unresolved issues," he said. Nevertheless, he said he expected to hear from administration officials in the coming days as they "start to turn up the decibel level."
Obama was intent on doing that. He entrusted Vice President Joe Biden, a longtime voice in the Senate, to "focus on this issue day and night until it gets done."
And, along with summoning some of his own top brass, the president brought in what he called "some of the most able statesmen from both parties." They included former secretaries of state Madeleine Albright, James Baker III and Henry Kissinger, former defense secretaries William Perry and William Cohen and former National Security Adviser Brent Scowcroft.
"This is not a matter that can be delayed," Obama said. "Every month that goes by without a treaty means that we are not able to verify what's going on on the ground in Russia. And if we delay indefinitely, American leadership on nonproliferation and America's national security will be weakened."
Two potential Republican candidates for president — Mitt Romney and Sarah Palin — both have come out against the pact.
As for the public, two-thirds of Americans believe the Senate should ratify the nuclear arms reduction treaty with Russia, according to an Associated Press-GfK Poll conducted earlier this month. Besides a strong majority of Democrats, supporters include more than six in 10 Republicans.
Associated Press writers Donna Cassata, Desmond Butler, Lolita C. Baldor, Alan Fram and Jim Kuhnhenn contributed to this story.
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