WASHINGTON – President Barack Obama sternly proclaimed ratification of the U.S.-Russia nuclear arms treaty "a national security imperative" Thursday, saying the Senate must act before Congress goes home for the year.

Lobbying hard for votes from the White House, Obama he expressed confidence he would be able to get enough votes to get the treaty passed, saying that every president since Ronald Reagan has been able to get such pacts through.

To apply pressure on the Senate, Obama surrounded himself for his statement with former secretaries of states and defense of both parties, who all support the treaty, along with leaders of his administration. He said the United States "cannot afford to gamble" with its ability to verify Russia's strategic nuclear arsenal — a central element of the treaty. Nor, he said, can this country risk losing Moscow's support on other matters of national security, including pressure on Iran over its suspected pursuit of nuclear weapons.

This is not about politics," Obama said from the Roosevelt Room. "It's about national security. This is not a matter than can be delayed.

The president insisted that the administration has taken the necessary time to do the treaty the right way, even as a key Republican senator on the matter, Jon Kyl of Arizona, has said that ratification should not be rushed during the current lame duck session.

When Obama was asked by a reporter if he had the votes, he replied: "I'm confident that we should be able to get the votes." Ratification would require 67 votes in the 100-member Senate.

The White House brought in former secretaries of state Madeleine Albright, James Baker and Henry Kissinger, former defense secretaries William Cohen and William Perry and former National Security Adviser Brent Scowcroft.

It was meant to be a showing of united statesmanship and strength for a White House thrown on the defensive by Kyl's push for a delay.

This is not a Democratic concept. This is not a Republican concept," Obama said. "This is a concept of American national security that has been promoted by Ronald Reagan, George H.W. Bush, Bill Clinton, George W. Bush and now my administration. We've taken the time to do this right.

The agreement would shrink the U.S. and Russian arsenals of strategic warheads and revive on-the-ground inspections that ceased when a previous treaty expired nearly a year ago.

The treaty has support from some moderate Republicans, but Kyl's opposition makes approval a tough climb since many in the GOP were looking to his assent before giving their backing. Democrats need at least eight Republican votes for ratification in the current Senate.

Once the newly elected Senate is seated in January, Democrats will need the support of at least 14 Republicans.

Ten of the newly elected Republican senators supported Kyl's call for delay, noting that no arms pacts with Russia has been ratified under a lame duck Congress. In a statement, they said the nuclear pact "would dramatically reduce the U.S. nuclear deterrent.

The White House is mounting an all-out push for ratification of the treaty, which Obama has made a top foreign policy priority.

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," Obama said. "And if we delay indefinitely, American leadership on nonproliferation and America's national security will be weakened.

Kyl, who's been seeking more money and focus on maintaining and modernizing the remaining arsenal, said more time was needed before moving forward.

When pressed on the issue Wednesday, Kyl told reporters, "We're talking in good faith.

Senate Majority Leader Harry Reid, D-Nev., issued a statement Wednesday supporting quick action on the treaty, saying he was "puzzled" by Kyl's stance.

But the administration's hopes suffered another hit when Republican Sen. George Voinovich, an Ohio moderate who is retiring this year, expressed his reservations about the treaty.

America's grand strategy approach towards Russia must be realistic, it must be agile, and as I have said it must take into account the interests of our NATO allies," Voinovich said in a statement. "I am deeply concerned the New START Treaty may once again undermine the confidence of our friends and allies in Central and Eastern Europe.

A clearly frustrated Lugar, the top Republican on the Senate Foreign Relations Committee and a treaty supporter, suggested the administration press ahead with a vote despite the opposition of Kyl and others. Lugar, a leading voice on nuclear issues, said if the White House and Democrats wait until next year and the new Congress, the process would have to start anew with hearings, committee votes and a greater risk that the treaty won't be ratified.

This is a situation of some national security peril," Lugar told reporters.

Obama and Russian President Dmitry Medvedev signed the pact in Prague in April. Obama met with Medvedev last weekend on the sidelines of an economic meeting in Japan and emphasized his commitment to advancing the treaty during the lame-duck session.

The treaty would reduce U.S. and Russian strategic warheads to 1,550 for each country from the current ceiling of 2,200. It also would set up new procedures to allow both countries to inspect each other's arsenals to verify compliance.

Kerry said there were no substantive disagreements on the treaty itself and that a major objection of Kyl's should have been removed when the administration pledged an additional $4.1 billion for weapons modernization programs.

Republicans have argued that the treaty would limit U.S. missile defense options and does not provide adequate procedures to verify that Russia is living up to its terms.

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AP White House Correspondent Ben Feller contributed to this story.