WASHINGTON — President Barack Obama has written to Russian President Dmitry Medvedev suggesting U.S. plans for a missile defense system in Eastern Europe might be unnecessary if Moscow helped in blocking Iran's progress toward building long-range missiles, senior administration officials said today.

Plans for deploying U.S. missile defenses in Poland and the Czech Republic, ostensibly to guard against Iranian attacks on U.S. allies in Europe, are among a host of issues that soured U.S.-Russia relations during the former Bush administration. There have been indications Obama, who has vowed to shake up American foreign policy, might be willing to set aside the missile defense system.

Medvedev voiced readiness to cooperate with Washington but denied receiving an offer of trade-off on missile defense and Iran. The Kremlin did call Obama's letter a "positive" development.

One senior U.S. official, speaking on condition of anonymity, said Obama sent a letter to Medvedev that "covered a broad range of issues, including missile defense and how it relates to the Iranian threat."

"The suggestion is that need for missile defense deployment could become unnecessary if, working together with Russia, the Iran missile threat is addressed," the official told The Associated Press.