The White House Thursday sent a new START arms treaty to Senate, backed by a call for 80 billion dollars to help modernize the US nuclear stockpile, in a first step towards ratifying the historic deal with Russia.

"The treaty will enhance the national security of the United States," President Barack Obama said in a message transmitting the treaty to senators.

"It mandates mutual reductions and limitations on the world's two largest nuclear arsenals," the president added, saying the treaty would also ensure both Moscow and Washington could "verify that the other party is complying with its obligations."

The new arms reduction deal was signed by Obama and his Russian counterpart Dmitry Medvedev in a landmark ceremony in Prague in April, and commits the two former Cold War foes to slashing their nuclear arsenals.

Each nation will be allowed a maximum of 1,550 deployed warheads, about 30 percent lower than a limit set in 2002. They are also restricted to 700 air, ground and submarine-launched intercontinental ballistic missiles that carry warheads.

But the treaty must be ratified by both the Kremlin and the US Senate, where it faces Republican opposition, before it can go into effect.

Seeking to allay fears that the move could leave the United States vulnerable, Obama also sent Congress a classified report detailing plans backed by 80 billion dollars in investments "to sustain and modernize the nuclear weapons complex over the next decade."

The report sets out a comprehensive plan for sustaining "a strong nuclear deterrent for the duration of the new START treaty and beyond," the White House said in a statement.

The United States "will continue to maintain a strong nuclear deterrent under this treaty," Obama vowed in his statement.

He added it "preserves our ability to determine for ourselves the composition and structure of our strategic forces within the treaty's overall limits, and to modernize those forces."

Obama called Medvedev earlier Thursday to tell him the treaty was going to the Senate, the White House said.

"The presidents stressed the importance of completing the ratification process in both countries as soon as possible," a statement said.

Adding his voice to the White House bid to overcome lingering reservations in Congress, Defense Secretary Robert Gates, who served under the former Republican Bush administration, said the new treaty "has the unanimous support of America's military leadership."

Apart from cutting nuclear arsenals and setting up a verification regime, "the treaty preserves the US nuclear arsenal as a vital pillar of our nation's and our allies' security posture," Gates wrote in an opinion piece in the Wall Street Journal.

He argued the extra 80 billion dollars in funding would be spent over "the next decade to rebuild and sustain America's aging nuclear infrastructure especially our national weapons labs, and our science, technology and engineering base."

Such a plan meets a key demand from Republicans, who have also cautioned they will oppose the pact if they think it will hamper US missile defense plans bitterly opposed by Russia.

Past arms control agreements have historically sailed through the US Senate with minimal opposition, but the treaty faces deep skepticism from Republicans looking to deny Obama a major diplomatic victory in an election year.

Treaty ratification requires 67 votes, but Democrats and their two independent allies hold only 59 seats in the 100-member Senate, meaning they will need to rally at least eight Republicans.

Obama has said he wants to see the treaty ratified this year. Senate Majority Leader Harry Reid said last month the ratification might have to wait until 2011, after November mid-terms elections.

"I'm going to do everything I can to advance this as quickly as I can. It may take until the first of the year to get it done, but I think it's important we try to get this done," he said.