US President Barack Obama called Thursday on the Senate to approve a landmark nuclear weapons deal this year, before a newly elected crop of skeptical Republican legislators take office.

The new Strategic Arms Reduction Treaty (START), which would slash the nuclear arsenals of the world's two largest nuclear powers, was negotiated this year to replace a similar treaty that expired.

Obama appealed to the Republicans to help approve the treaty when Congress returns on November 15, after the party put up stiff opposition to the new deal fearing it could hamper US missile defense plans.

"This is not a traditionally Democratic or Republican issue, but, rather, an issue of American national security," Obama said at a cabinet meeting, two days after Republicans posted strong gains in congressional elections.

"I'm hopeful that we can get that done... and send a strong signal to Russia that we're serious about reducing nuclear arsenals, but also send a signal to the world that we're serious about non-proliferation," Obama said.

The new Congress takes office in January, with Republicans set to take control of the House of Representatives and to add members to the Senate. The next two months are known as a "lame duck" session, in which outgoing lawmakers often shy away from major legislation.

But START faced uncertain prospects even in the current Congress. Under the US constitution, treaties need the approval of two-thirds of the Senate.

The START treaty -- signed by Russian President Dmitry Medvedev and Obama at an elaborate ceremony in Prague in April -- restricts each nation to a maximum of 1,550 deployed warheads, a cut of about 30 percent from a limit set in 2002.

The treaty enjoys the support of Senator Richard Lugar, the top Republican on the Foreign Relations Committee, along with several former Republican secretaries of state including Henry Kissinger.

But a growing number of Republicans have voiced opposition, saying it would impede the US ability to set up missile defenses against potential threats such as Iran and does not account for a rising China.

Former Massachusetts governor Mitt Romney, who is expected to seek the Republican nomination to run against Obama in 2012, has led the charge criticizing START.

Secretary of State Hillary Clinton also called Thursday for the Senate to approve the START treaty in its lame-duck session.

"We believe we have enough votes to pass it in the Senate. It's just a question of when it will be brought to the vote," Clinton told reporters during a visit to Wellington, New Zealand, during a tour of Asia.

Russia has warned that the treaty could go back to the drawing board if the United States does not ratify it soon.

After the US elections, the foreign affairs committee of the Duma, Russia's parliament, withdrew its recommendation for the full assembly to approve the treaty.

"If the 'lame duck' senators from the old make-up cannot do this in the next weeks, then the chances of ratification in the new Senate will be radically lower than they were until now," committee chairman Konstantin Kosachev said.