US-Russia relations could suffer if senators fail to ratify a new arms control treaty, with Moscow possibly refusing to back Washington's policy on Iran, a top US official said Tuesday.

Forging a new Strategic Arms Reduction Treaty (START) has bolstered cooperation between the former Cold War foes on national security issues, paving the way for Moscow to support new UN sanctions against Iran over its nuclear program, said Rose Gottemoeller, who helped negotiate the accord.

"We have gotten some immediate benefits into the Russian relationship from working so closely together on the START deal. I see an effect particularly on our ability to work with the Russians on Iran," said Gottemoeller, assistant secretary of state for verification, compliance and implementation.

"The result was I think their full support for this very good sanctions resolution that was passed after the treaty was signed in April. And the Russians have been working with us in other ways on Iran that's very important.

"So I think there are some perhaps penalties that we would pay in the US-Russia relationship" if the US Senate fails to ratify the START treaty, she told reporters, saying any such defeat would damage America's global leadership.

Gottemoeller said allowing the START deal to collapse would mean the United States would no longer be able to closely monitor Russia's nuclear weaponry, as the new treaty allows for intrusive inspections.

"I think primarily we lose our eyes and ears inside the Russian federation," she said.

Without the nuclear arms reduction accord, the United States could be forced to spend more money on its nuclear arsenal at a time when the defense budget is coming under strain due to a costly war in Afghanistan and a troubled economy.

"I think our military leadership would prefer to be concentrating on what's needed for our soldiers in Afghanistan than having to -- through worst-case planning -- pour resources into the nuclear forces."

With the Senate possibly voting on the treaty before legislative elections in November, the diplomat said she was encouraged by recent signs of "positive momentum" but declined to predict how many Republicans might vote for the agreement.

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 ratifying the treaty.

Ratification 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.

Some Republican opponents have argued that the treaty could jeopardize US missile defense projects and that Washington needs to do more to modernize its nuclear stockpile in the face of concerns over Iran.