A group of US House Republicans urged the US Senate Tuesday to delay action on a landmark treaty with Russia until next year, citing worries about missile defense and upkeep of the US atomic arsenal.

"We are troubled by the administration's push to ratify the New START Treaty amid outstanding concerns regarding Russian intentions, missile defense limitations, and nuclear modernization," they told Senate leaders in a letter.

Representative Buck McKeon, the top Republican on the House Armed Services Committee, led fellow Republicans from the panel in signing the message of opposition to the new Strategic Arms Reduction Treaty (START).

The lawmakers acknowledged that they have no role in the accord's ratification, strictly the purview of the Senate under the US Constitution, but urged a delay until after a year-end "lame duck" session."

Republicans will formally retake the House of Representatives and see their numbers swell in the Senate when a new Congress convenes in January.

The 100-seat Senate currently counts 56 Democrats and two independents who vote with them, and ratification requires 67 votes. Republicans hold 42 seats now but that number will rise to 47 when a new Congress arrives.

US President Barack Obama, who has made approving the treaty a centerpiece of his effort to "reset" relations with Russia, has pushed for the Senate to act this year after months of congressional scrutiny.

The treaty has the support of nearly every past US foreign policy and national security heavyweight, the Pentagon, US spy chief, NATO, and Russia, where lawmakers say they will act only after the US Senate does.

But Republicans, many eager to deny Obama a major diplomatic victory, have sought to delay action.

The agreement restricts each nation to a maximum of 1,550 deployed warheads, a cut of about 30 percent from a limit set in 2002, and 800 launchers and bombers.

The agreement, which has broad US public support, would also return US inspectors who have been unable to monitor Russia's arsenal since the agreement's predecessor lapsed in December 2009.

Experts say it does not include binding language restricting US missile defense plans.