President Obama sent a secret letter to Russia's president last month suggesting he would back off deploying a new missile-defense system in Eastern Europe if Russia would help stop Iran from developing long-range weapons, U.S. officials said Monday.

WASHINGTON — President Obama sent a secret letter to Russia’s president last month suggesting he would back off deploying a new missile-defense system in Eastern Europe if Russia would help stop Iran from developing long-range weapons, U.S. officials said Monday.

The letter to President Dmitri Medvedev was hand-delivered in Moscow by top administration officials three weeks ago. It said the United States would not need to proceed with the interceptor system, which has been vehemently opposed by Russia since it was proposed by the Bush administration, if Iran halted any efforts to build nuclear warheads and ballistic missiles.

Russia’s military, diplomatic and commercial ties to Iran give it some influence there, but it has often resisted the United States’ hard line against Iran.

“It’s almost saying to them put up or shut up,” said a senior administration official. “It’s not that the Russians get to say, ‘We’ll try and therefore you have to suspend.’ It says the threat has to go away.”

Russia has not responded, but a Russian official said Monday that Foreign Minister Sergey Lavrov would discuss missile defense with Secretary of State Hillary Rodham Clinton when they meet Friday in Geneva. Obama and Medvedev then will meet for the first time April 2 in London, officials said Monday.

Obama’s letter, sent in response to one he received from Medvedev shortly after his inauguration, represents part of an effort to “press the reset button” on U.S.-Russian relations, as Vice President Joseph Biden put it last month. Among other things, the letter discussed negotiations to extend a strategic arms treaty expiring this year and cooperation in opening supply routes to Afghanistan.

The plan to build a high-tech radar facility in the Czech Republic and deploy 10 interceptor missiles in Poland — a part of the world that Russia once considered its sphere of influence — was a top priority for President Bush to deter Iran in case it developed a nuclear warhead to fit atop its long-range missiles. Bush never accepted a Russian proposal to install part of the missile-defense system on its territory and jointly operate it.

Now the Obama administration appears to be reconsidering that idea, although it is not clear if it would want to put part of the system on Russian soil where it could be flipped on or off by Russians.

Obama has been lukewarm on missile defense, saying he supports it only if it can be proved technically effective and affordable.