Senate Majority Leader Harry Reid vowed Thursday to overcome Republican efforts to delay ratification of a nuclear arms-reduction treaty with Russia, as the chamber neared the end of its first day of debate on the agreement.

"We are in session, if necessary, up to Jan. 5," Reid told reporters. The Nevada Democrat said he regretted the slow pace of the opening day's debate. "No one can say that anyone is being jammed on this," he said.

A 66-32 Senate vote Wednesday to start consideration of the treaty highlighted how narrow a majority President Obama and his Democratic Party may have for a treaty that requires two-thirds of the 100-member Senate for approval.

Democrats control 58 votes in the Senate until next month, when Republicans will have six more seats as a result of November's midterm elections.

Some Republicans have sought to delay consideration of the treaty until next year and are considering offering amendments that would slow debate during the postelection session. Republicans filed only one amendment Thursday, Reid said.

"There's a great deal of discussion that needs to be made as a predicate" before amendments would be offered, said Arizona Sen. Jon Kyl, the Senate's second-ranking Republican, who leads his party's critics of the treaty.

Senate Foreign Relations Committee Chairman John Kerry (D., Mass.) said that there might be as many as 20 Republican-backed amendments "floating around" for possible consideration.

But Democrats say they will not support amending the treaty because it would require a renegotiation with the Russians. "We're prepared to stay as long as necessary," Kerry said. "We are prepared to get this treaty done."

The treaty is part of Obama's attempt to reset U.S. relations with Russia, and ratification would be a victory on one of his top foreign-policy priorities. The administration and Senate leaders have said they have enough support to get the two-thirds majority needed to approve ratification.

But a dozen treaty opponents lined up behind Kyl at a news conference Thursday to criticize Reid's decision to proceed on the treaty and the spending bill simultaneously. Most favored delaying the START treaty until next year, with some calling for renegotiating elements of the treaty.

Critics say the treaty limits U.S. options for developing missile defenses, a project Russia has opposed. They also argue that the new accord's verification standards are not strong enough and that Obama hasn't given enough assurances that the existing U.S. arsenal will be adequately maintained.

Defense Secretary Robert M. Gates, speaking at a news conference with Secretary of State Hillary Rodham Clinton, said Thursday: "I think there were some legitimate concerns, but frankly, I think they've been addressed. I think there were some misunderstandings, frankly, on missile defense."