WASHINGTON (Reuters) - The United States has made it clear to Russia that delivering an anti-aircraft system to Iran would have severe consequences for U.S. ties with Moscow, a senior advisor to President Obama said Tuesday.

In a generally upbeat assessment of ties with Russia, Gary Samore, White House coordinator for arms control, weapons of mass destruction proliferation and terrorism, said he thought Russia understood Washington’s position and would be surprised if Moscow shipped the S-300 anti-aircraft system that Iran has ordered.

“We’ve made it very clear to the Russians that that would have a very significant impact on our bilateral relations,” said Samore. “I think the Russians understand that the consequences would be very severe.”

Tehran has urged Russia not to bow to Western pressure over the sale of the system which, analysts say, could help Iran thwart any attempt to bomb Iran’s nuclear facilities.

The United States and Israel have refused to rule out military action against Iran if diplomacy fails to resolve the dispute over its nuclear facilities. Tehran says its nuclear program is for peaceful purposes, but Western governments believe it is aimed at bomb-making.

Washington is pressing other global powers to agree to a fourth round of U.N. sanctions against Tehran over its refusal to halt its nuclear work, but Samore said Iran’s program had suffered technical setbacks, giving diplomacy a bit more time.

“The nuclear clock is not moving as quickly as some feared,” he said.

DEFENDING RESET WITH RUSSIA

Samore defended the Obama administration’s decision this week to revive an agreement with Russia in which the two countries would cooperate on civilian nuclear energy, saying the Russians had been more cooperative on issues ranging from dealing with Iran to reducing nuclear arms.

But he stopped short of saying that the proposed nuclear deal would be withdrawn if the Russians sent the anti-aircraft system to Iran, or backed away from supporting a new resolution on U.N. Security Council sanctions against Iran.

“I think we are seeing good cooperation from the Russians and I think that will be apparent to everybody once the Security Council takes action,” Samore said. “I think we will get a good resolution with Russian and Chinese support.”

Washington’s effort to renew the civilian nuclear deal with Russia is the latest attempt to “reset” U.S. relations with Russia, one of President Barack Obama’s foreign policy priorities.

The civilian nuclear deal was shelved almost two years ago over Russia’s war with Georgia, when relations between Washington and Moscow reached a post-Cold War low.

The agreement is not a treaty but it must be submitted to Congress for a 90 day review and lawmakers can vote to kill it before it becomes effective.

Some Republicans in Congress have expressed concern that Obama is going too far in Russia’s direction before getting Moscow to sign on to a tough sanctions resolution on Iran.

“By trading this agreement for Russian support for a weak, meaningless round of Iran sanctions at the UN Security Council, the U.S. has severely hampered its own efforts to isolate the Iranian regime,” said Ileana Ros-Lehtinen, the ranking Republican on the House Foreign Affairs Committee.