WASHINGTON (Reuters) - U.S. President Barack Obama said on Tuesday he wanted to work with Russia to resolve a nuclear stand-off with Iran but denied reports he had offered to slow deployment of a missile defense shield in exchange for Moscow’s help.

The New York Times reported that Obama had sent a letter to Russian President Dmitry Medvedev suggesting he would back off deploying a system in eastern Europe to intercept and destroy missiles, a move Russia sees as a military threat, if Moscow helped stop Iran from developing long-range weapons.

“What I said in the letter is what I have said publicly, which is that the missile defense that we have talked about deploying is directed toward, not Russia, but Iran,” Obama said after meeting British Prime Minister Gordon Brown.

“And what I said ... was that, obviously, to the extent that we are lessening Iran’s commitment to nuclear weapons, then that reduces the pressure for, or the need for a missile defense system,” he said.

Obama’s defense secretary, Robert Gates, said Washington wanted to reopen dialogue with Moscow on Iran. There were two options, he said -- to work together to persuade Iran not to go ahead with their ballistic missile program, or make Russia a “full partner” in the defense shield.

White House spokesman Robert Gibbs stressed the linkage between the missile shield and Iran at a White House briefing.

“If working with our allies and working with Russia we can eliminate the threat, then you eliminate the driving force behind that system to combat that threat,”.

Moscow, which plans to start up a nuclear reactor at Iran’s Bushehr plant by the end of the year, has used its veto in the United Nations Security Council on a number of occasions to water down or defeat U.S.-led efforts to impose tougher sanctions on Iran.

The Obama administration has said it wants to “reset” U.S.-Russian ties, which deteriorated under former U.S. President George W. Bush and then Russian President Vladimir Putin, partly because of the plans to deploy the shield.

MOSCOW WILLING TO TALK

Putin’s successor, Medvedev, told a news conference that Moscow was willing to talk to Washington about the shield but that it saw Iran’s nuclear program as a separate issue.

“If the new (U.S.) administration shows common sense and offers a new (missile defense) structure which would satisfy European (needs) ... and would be acceptable for us, we are ready to discuss it,” Medvedev said on a visit to Madrid.

“If we are talking about any ‘swaps’ (Iran for missile defense) this is not how the question is being put. This would not be productive,” he said.

Russian President Dmitry Medvedev speaks at the United Russia party congress in Moscow, November 20, 2008. REUTERS/Alexander Natruskin

U.S. officials have said the United States will go ahead with the planned deployment of the missile shield in eastern Europe, but only if it is shown to work and is cost-effective.

The plan to site missiles and a radar tracking station in former Communist satellite states Poland and the Czech Republic has angered Moscow, which sees it as a threat, despite U.S. insistence that it is aimed at rogue missiles from Iran.

The United States and some European nations fear Iran is trying to build atomic weapons and are concerned at its development of ballistic rockets that could be used to carry any nuclear warheads great distances.

Tehran insists its pursuit of a nuclear capability is purely for the peaceful generation of electricity.

Obama has said he is prepared to offer Iran economic incentives if it abandons its nuclear program but he has also warned of tougher economic sanctions if it pushes ahead.

The United States and five other powers, Britain, France, Germany, Russia and China, said on Tuesday they were committed to direct talks with Iran, a switch from Bush’s policy of trying to isolate the Islamic Republic.

On Capitol Hill, a key Republican said Obama should consider engaging Iran more directly.

“Among other steps, the possibility of establishing a U.S. visa office or some similar diplomatic presence in Iran should be on the table,” said Indiana Senator Richard Lugar, the ranking Republican on the Senate Foreign Relations Committee.