In a bid to win approval of a nuclear arms control treaty with Russia before newly energized Republicans increase their clout in the Senate, the Obama administration is offering to add billions of dollars in funding for the U.S. nuclear arsenal.

A congressional aide briefed on the proposed deal said White House officials outlined it to Republican Sen. Jon Kyl, who is seen as the key to winning enough support to ratify the New START treaty. The aide spoke on condition of anonymity because he was not authorized to comment.

The offer was for a boost of $4.1 billion in funding between 2012-2016 for the nuclear weapons complex that will go to maintaining and modernizing the arsenal and the laboratories that oversee that effort. Of that, $1 billion would cover a deficit in the pension fund for the agency in charge of the stockpile and laboratories.

The additional money comes on top of an additional $10 billion the administration had already agreed to over 10 years.

The administration is scrambling to get enough Republican support in the Senate to ratify the New START treaty before the Democrats' majority shrinks by six in January. In a sign of the urgency of the administration's pitch, government officials traveled to Kyl's home state of Arizona to brief him on the proposal, the aide said. Officials also briefed Republican Sen. Bob Corker of Tennessee.

"This is a huge increase," said Daryl Kimball, head of the private Arms Control Association. He noted that it is not certain that Congress will approve the funding, which will in any case have to be appropriated over time for each of the years in the proposal.

The aide said that the administration has also conveyed to Republican lawmakers that its offer is contingent on passing the treaty before the end of the year and that Democratic support for the increased funding would likely evaporate, if the treaty stalls.

Details of the proposal were made available to Senate staff, including aides on the Appropriations Committee Friday.

It was not clear whether the offer had swayed Kyl and his office declined to comment.

In Yokohama, Japan, where President Barack Obama was attending a Pacific Rim summit, his national security adviser, Tom Donilon, said he couldn't confirm the report. But he told reporters the administration has tried to address "what had been a real shortfall in funding for maintaining and enhancing the nation's nuclear infrastructure."

Obama was to meet on Sunday with Russian President Dmitry Medvedev on the summit margins. Donilon said his message would be the administration's commitment to getting New START approved.

"It's important on the merits in terms of the arms control aspects of the treaty," the adviser said. "It's important for U.S. leadership in the world on the nonproliferation agenda. And it's important for the U.S.-Russia relationship."

The treaty would reduce the limit on 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.

Kyl has maintained that boosting funding for the stockpile would ease Republican concerns about the treaty by demonstrating that the administration is serious about maintaining a robust U.S. nuclear deterrent.

A number of his Republican colleagues have said they will follow Kyl's lead on the treaty, so his approval could push support beyond the 67 votes the administration needs for ratification, although many Republicans still are likely to oppose it.

Some 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. Advocates dispute both charges.

The administration is worried that ratification could slip out of reach if a vote were to be delayed.

Failure to win passage could trip up one of the administration's top foreign policy goals: improving relations with Russia. The treaty, signed in April by Obama and Medvedev, has been the most tangible sign of success, and failure to get it ratified could be viewed as a rebuke in Moscow. It also would leave Obama's push for even greater restrictions on the world's nuclear arsenal in doubt.