A senior US official on Monday predicted a vote on a landmark arms reduction treaty with Russia before mid-term elections, but refused to predict if it would pass amid Republican opposition.

Rose Gottemoeller, who helped negotiate the new Strategic Arms Reduction Treaty (START), said the Senate was working "very hard" and "I hope actually (to) get a vote on the floor in the next couple of weeks."

"These are all signs to me of momentum -- and of positive momentum -- but as to the results, I think, well, it's still up in the air," said Gottemoeller, assistant secretary of state for verification, compliance and implementation.

Gottemoeller said that Senator John Kerry had promised that the Senate Foreign Relations Committee, which he chairs, would take up START on Thursday.

"The reason I'm feeling optimistic is that we have a clear signal from Senator Kerry," said Gottemoeller, who was addressing a forum at Georgetown University.

But senators, who re-entered session on Monday, are expected to adjourn within a month to campaign for November 2 mid-term elections, in which President Barack Obama's Democratic Party is seen at risk.

Richard Lugar, the top-ranking Republican on the Senate Foreign Relations Committee, is the only senator from his party who has come out in support of ratification of the new START treaty.

Ratification of a treaty requires 67 votes in the Senate. Democrats and their two independent allies hold 59 seats, meaning they cannot approve START without Republican support.

The treaty -- signed by Obama and Russian President Dmitry Medvedev 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 Obama administration says that the treaty will strengthen global non-proliferation efforts and marks a turning point in often strained US-Russia relations.

Some Republicans, along with independent Senator Joseph Lieberman, have argued that the United States needs to do more to modernize its nuclear stockpile in the face of concerns about Iran.