Washington (CNN) -- Senate Republicans mounted a counter-attack Sunday against ratifying a new nuclear arms treaty with Russia this year, trying to put off a vote that Democrats say they will win if it is held.
Senate Minority Leader Mitch McConnell of Kentucky led the way, telling CNN's "State of the Union" that members of his party need more time to consider the START accord.
"I've decided I cannot support the treaty," McConnell said in his first outright rejection of ratifying the treaty during the current lame-duck session of Congress.
The treaty would resume mutual inspections of U.S. and Russian nuclear arsenals, while limiting both nations to 1,550 warheads and 700 launchers each. On Sunday, Democrats rejected a Republican amendment to the treaty's preamble that would have added a reference to tactical nuclear weapons, which are not covered by the pact.
Republican senators are "uneasy" about the treaty, and trying to get a vote before Christmas was not the best way to "get the support of people like me," McConnell said.
His unequivocal stance increased the GOP's public opposition to ratification, which would require at least 10 GOP senators to vote with the Democrats to reach the two-thirds majority of 67 needed.
The Democratic caucus has 58 members, but one of them, Sen. Ron Wyden of Oregon, is preparing for prostate cancer surgery Monday and is expected to miss the rest of the current lame-duck session that expires January 4.
If the vote gets put off to the new Congress, as Republicans want, the number of GOP votes needed for ratification rises to at least 14 because the Democrats will have a diminished majority of 53 seats.
McConnell's comments prompted a response from his Democratic counterpart, Senate Majority Leader Harry Reid of Nevada, who issued a statement saying he was "deeply disappointed" at McConnell's opposition to the treaty.
Reid's statement noted that "respected Republican leaders" including former President George H.W. Bush and several former secretaries of state, as well as the current military leadership all called for ratification.
In addition, Reid's statement said, the proposed treaty has been available since May and the Obama administration has answered questions from senators and taken steps to address concerns. For example, the administration has committed to increased spending on modernizing the U.S. nuclear arsenal at the request of Sen. Jon Kyl, R-Arizona, who had been leading the GOP opposition to the treaty.
"I know many senators, including my colleagues on the other side of the aisle, who share the belief that this treaty is too critical to our national security to delay, and I look forward to strong bipartisan support to pass this treaty before we end this session of Congress," Reid's statement concluded.
Later Sunday, Reid filed a cloture motion -- a necessary procedural step to end debate and set up a vote.
"After months of consideration and five days of open and robust debate, it is time to move forward on a treaty that will help reverse nuclear proliferation and make it harder for terrorists to get their hands on a nuclear weapon. Every day we delay is another day we do not have inspectors on the ground in Russia monitoring their nuclear arsenal," he said in a statement.
Democratic Sen. John Kerry, the chairman of the Senate Foreign Relations Committee, predicted Sunday that Democrats have the necessary support for ratification and that the vote would occur in the coming days.
"I believe it will pass, and I believe there will be a vote," Kerry said on the ABC program "This Week."
However, the ranking Republican on the Senate panel, Richard Lugar of Indiana, said he was uncertain that the vote would occur before the lame-duck session expires.
"Several Republicans will support it, and I join the chairman (Kerry) in believing that there are the votes there," said Lugar, who backs ratification. "The problem is really getting to that final vote."
Lugar noted that the Senate still needs to debate Republican amendments to the treaty. Any change in the language or substance of the pact would require reopening negotiations with Russia, effectively killing the agreement.
So far, Democrats have defeated the two Republican amendments proposed -- Sunday's attempt to add a reference to tactical nuclear weapons, and a Saturday bid by Sen. John McCain of Arizona to remove from the preamble language recognizing a relationship between offensive and defensive weapons. In both cases, however, Democrats were at least seven votes shy of the 67 they will need to ratify the treaty.
Republican Sen. Lindsey Graham, R-South Carolina, on Sunday continued questioning the language cited in the failed McCain amendment, telling the CBS program "Face the Nation" that it could undermine future development of U.S. missile defense systems.
According to Graham, Russia could object to continuing U.S. development of missile defense capability as a violation of the treaty and withdraw from it.
Kyl, appearing on "FOX News Sunday," also challenged the language in the preamble, which he said changes the past U.S. stance by linking offensive and defensive weapons.
"In the last arms control treaty with Russia in 2002 we absolutely separated the two issues," Kyl said. Now, he said, the Democrats were insisting the treaty can't be changed.
If that's the case, Kyl said, "we're just a rubber stamp for the administration and the Russians, the administration that for the first time wasn't willing to stand up to the Russians and say, 'You're not going to implicate our missile defenses.' "
However, Democratic Sen. Carl Levin of Michigan, the chairman of the Senate Armed Services Committee, labeled the missile defense concern a "straw man" argument without substance. The nation's top military leaders say "there is no restriction, no limitations whatsoever" on missile defense in the treaty, Levin said.
Lugar also challenged some of the GOP arguments, saying the resumed inspections under the new treaty were essential for verifying compliance by Russia. In addition, the treaty represents new opportunities to engage with Russia on important issues in the continuing evolution of relations between the countries after the Cold War era, he noted.
"To throw away all of those opportunities simply because some feel the Russians are no longer relevant or we should just simply build whatever we want to quite apart from the Russians seems to me is an illogical stance, but we're hearing a lot of that," Lugar said on the ABC program.
Democrats argued that the Senate has plenty of time to consider further Republican amendments and debate the treaty before the new Congress gets sworn in during the first week of January.
Previous arms control treaties have taken a similar amount of time to debate, Levin noted on the CBS program.
The Senate is expected to go into a closed session Monday afternoon to discuss classified information related to the treaty.
On Saturday, President Barack Obama sent letters to McConnell and Reid expressing his support for the accord.
"The New START treaty places no limitations on the development or deployment of our missile defense programs," Obama wrote.
CNN's Gabriella Schwarz contributed to this report.