US Secretary of State Hillary Clinton on Wednesday urged the Senate to move quickly to pass the new US-Russian nuclear arms reduction treaty when it resumes debate next month.

The US Senate Foreign Relations Committee last week delayed until mid-September its vote on approving the New Strategic Arms Reduction Treaty (START), the successor to one that expired in December.

Committee chairman John Kerry's decision to give Democrats and Republicans more "time to review the underlying materials ... is a gesture of good faith and underscores the tradition of bipartisan support," Clinton told reporters.

"But when the Senate returns, they must act, because our national security is at risk," the chief US diplomat said.

"There is an urgency to ratify this treaty because we currently lack verification measures with Russia, which only hurts our national security interests," she said.

"Our ability to know and understand changes in Russia's nuclear arsenal will erode without the treaty," she said, adding no inspectors have been in place since the former START treaty expired in December.

Clinton said she looked forward to working with senators over the next few weeks to move the treaty from committee to the full senate for a vote.

Committee approval would send the new START to the entire Senate, where 67 votes are needed for ratification, a process President Barack Obama has said he would like to see completed in 2010.

The delay in committee debate pushes the final debate on the treaty, a top White House priority, to the last stretch before November mid-term elections at a time when Republicans are eager to deny the president any major victories.

Obama's Democratic allies and their two independent allies control only 59 votes, meaning the treaty's backers will need to rally at least eight Republicans to approve the pact.

Some Republican senators have indicated they are inclined to back the pact but say they worry about the effects on the US nuclear deterrent and that they want to energize work at national nuclear laboratories to ensure the safety and reliability of the US arsenal.

Clinton said: "I'm confident about the prospects for ratification."

The new START, which President Barack Obama and Russian President Dmitry Medvedev signed in a landmark ceremony in Prague in April, 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 nuclear intercontinental ballistic missiles.