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

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 Biden.

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

Failing to ratify the treaty, Powell said, could leave the United States 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 Sens. George V. Voinovich (R., Ohio) and John McCain (R., Ariz.), who indicated they would like to finish work on the treaty this year.

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

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

In an interview for broadcast Wednesday on CNN, Putin said that if 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.

Last month, Obama met 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 K. Albright, James A. Baker 3d, 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 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.