US President Barack Obama Thursday said he hoped that a landmark nuclear weapons deal with Russia would win Congress approval before the end of this year.

The new Strategic Arms Reduction Treaty (START) was negotiated earlier this year to replace a similar treaty which expired at the end of December.

Obama appealed to 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. So the next two months are known as a "lame duck" session, in which outgoing lawmakers often shy away from major legislation.

But START was facing trouble 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.

US Defense Secretary Robert Gates echoed Obama's appeal, urging the Senate to ratify a treaty to ensure the resumption of inspections of Russia's arsenal.

His press secretary, Geoff Morrell, told reporters that Gates "and many other former defense secretaries and national security officials, from both parties, have frequently voiced their strong belief that this treaty is absolutely critical to the effectiveness of our nuclear arsenal, our knowledge of Russian nuclear capabilities, and US national security overall."

In the Senate, the treaty enjoys the support of 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 future potential threats such as Iran.

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.