President Barack Obama rallied support for a stalled nuclear treaty from former Secretary of State Colin Powell Wednesday, as Republican lawmakers indicated a greater willingness to ratify the agreement with Russia by the end of the year.

Both Obama and Powell warned of grave consequences if the Senate fails to ratify the New START pact, which would reduce how many strategic warheads the United States and Russia could hold and set up a system so each could inspect and verify the other's arsenal.

"When you have uncertainty in the area of nuclear weapons, that's a much more dangerous world to live in," Obama said from the Oval Office after a meeting with Powell and Vice President Joe Biden.

Powell, a retired four-star Army general and former Joint Chiefs of Staff chairman, said he fully supports the treaty, and believes Obama has adequately addressed the concerns of Republicans lawmakers over verification and modernization of the remaining U.S. nuclear arsenal.

Failing to ratify the treaty, Powell said, could leave the U.S. in a vulnerable position.

"We're not exactly sure what's going on in the Russian Federation, and they're not exactly sure what's going on in the United States," said Powell, who joined Obama in urging the Senate to ratify the treaty by the end of the year.

White House officials were cautiously optimistic Wednesday that momentum was building toward the treaty's ultimate ratification. Officials specifically pointed to comments this week from Republican Sens. George Voinovich and John McCain, who both indicated they'd like to finish work on the treaty this year.

More than a dozen Republican lawmakers met to discuss the administration's proposal on funding for modernizing the nuclear arsenal. Republicans, led by Sen. Jon Kyl, have argued that the Senate should not consider the treaty until more is done to maintain and improve the nuclear complex.

Republican Sen. Richard Lugar, a proponent of the treaty, said that he presented a letter at the meeting from the directors of the main U.S. nuclear laboratories backing the administration's plan and that it was well received by his colleagues.

Maine's moderate Republican Sen. Olympia Snowe credited the White House for working with Republicans to address their questions.

"Speaking for myself, I think there is that reflection and recognition that we can get it done this year," she said.

Leading Republican senators had argued that any action on START would have to come after the Senate addresses an extension of Bush-era tax rates and legislation to keep the government operating during the lame-duck session.

Republicans have threatened to block any other legislative action that reaches the floor of the Senate. But that threat, spelled out in a letter to Senate Majority Leader Harry Reid, specifically did not apply to the START treaty.

"Were we to finish the two things that we absolutely must do — taxes and spending — the more time that would be left for something else," Senate Republican leader Mitch McConnell of Kentucky said.

Reid also wants to hold votes on immigration legislation and ending the military's don't-ask, don't-tell policy for gay service members.

The White House has sought to cast the treaty's ratification as a national security imperative, not a political issue. Officials have underscored the need for the U.S. to show credibility in its newly improved relationship with Russia, whose support is vital in providing supply help for the war in Afghanistan and strengthening international pressure on Iran over its nuclear intentions.

"The relationships and trust that have built from the new START treaty spill over into a whole host of other national security issues that are of vital importance to America," Obama said Wednesday.

Russian Prime Minister Vladimir Putin has bluntly warned that his country would build up its nuclear forces if the U.S. doesn't ratify the treaty.

In an interview to be broadcast Wednesday on CNN, Putin said that START isn't ratified, "we'll have to react somehow," including deploying new nuclear technology. Putin said it would be "very dumb" for lawmakers to block the treaty.

The White House has launched a high-profile, high-stakes campaign to highlight the treaty's support both in the U.S. and around the world.

Powell, who served as Secretary of State under former President George W. Bush, is one of several current and former national security officials Obama has brought in to boost the case for the treaty's ratification.

Last month, the president met at the White House with what he called "some of the most able statesmen from both parties" to get support for START. 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.

In an opinion piece to be published Thursday in the Washington Post, former Republican secretaries of state Lawrence Eagleburger and George Shultz join Baker, Kissinger and Powell in calling for bipartisan support. "Republican presidents have long led the crucial fight to protect the United States against nuclear dangers," the group notes.

During a NATO summit in Portugal, Obama also secured the backing of several Eastern European nations, easing Voinovich's concerns that the treaty would undermine the confidence of allies in Central and Eastern Europe.

Whether Republicans will be swayed by the shows of support for the treaty was unclear. One top Republican, Sen. John Cornyn, said Wednesday that Powell's endorsement would have no impact on his vote.