Mr. Obama and Mr. Medvedev will meet for the first time on April 2 in London, officials said Monday.

Image The letter was hand-delivered to President Dmitri A. Medvedev, above, three weeks ago. Credit... Dmitry Astakhov/RIA Novosti, via Associated Press

Mr. Obama’s letter, sent in response to one he received from Mr. Medvedev shortly after Mr. Obama’s inauguration, is part of an effort to “press the reset button” on Russian-American relations, as Vice President Joseph R. Biden Jr. put it last month, officials in Washington said. Among other things, the letter discussed talks 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 George W. Bush to deter Iran in case it developed a nuclear warhead to fit atop its long-range missiles. Mr. Bush never accepted a Moscow proposal to install part of the missile defense system on its territory and jointly operate it so it could not be used against Russia.

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

Mr. Bush also emphasized the linkage between the Iranian threat and missile defense, but Mr. Obama’s overture reformulates it in a way intended to appeal to the Russians, who long ago soured on the Bush administration. Officials have been hinting at the possibility of an agreement in recent weeks, and Mr. Obama’s proposal was reported on Monday by a Moscow newspaper, Kommersant.

“If through strong diplomacy with Russia and our other partners we can reduce or eliminate that threat, it obviously shapes the way at which we look at missile defense,” Under Secretary of State William J. Burns said about the Iranian threat in an interview with the Russian news agency Interfax while in Moscow last month delivering Mr. Obama’s letter.

Attending a NATO meeting in Krakow, Poland, on Feb. 20, Defense Secretary Robert M. Gates said, “I told the Russians a year ago that if there were no Iranian missile program, there would be no need for the missile sites.” Mr. Obama’s inauguration, he added, offered the chance for a fresh start. “My hope is that now, with the new administration, the prospects for that kind of cooperation might have improved,” he said.