Russia’s Reaction on Missile Plan Leaves Iran Issue Hanging

President Obama’s decision to cancel an antimissile defense system in Eastern Europe earned a strong welcome from Russian leaders on Friday. Now, the question is whether Russia will do more to help prevent Iran from developing nuclear weapons..

Prime Minister Vladimir V. Putin, who had repeatedly assailed the antimissile system as a grievous threat to Russia’s security, called Mr. Obama’s decision “correct and brave.” President Dmitri A. Medvedev hinted that Russia would respond favorably to the decision to replace former President George W. Bush’s plan with a missile shield seen as less threatening to Moscow.

Still, neither leader offered any immediate indication that Russia would make specific concessions, especially on Iran, which has become a major stumbling block in relations between the countries. If Russia does not toughen its opposition to Iran’s nuclear program, analysts say, Mr. Obama may be vulnerable to criticism that he yielded to Russian complaints on the antimissile plan but received little in return.

“I hope our administration really thought this through and this was not about appeasing Russia, because I don’t think that justifies the decision,” said Riki Ellison, chairman of the Missile Defense Advocacy Alliance, a nonpartisan group that receives financing from defense contractors as well as private individuals who support missile defense.

The White House described the missile defense announcement as a response to changing Iranian capabilities, not as giving in to Russia, and said there was no quid pro quo. But the Obama administration needs support from Russia, which has veto power in the United Nations Security Council, in order to increase sanctions on Iran. American and European officials argue that Iran has carried out significant advances in recent months in developing a nuclear weapon.

Russia and China so far have resisted taking strong diplomatic steps or imposing tougher sanctions against Iran. Mr. Obama’s decision to remove one of the main irritants in relations between Washington and Moscow seems intended, in part, to alter that diplomatic equation and help increase the chances of addressing the impasse over Iran without resorting to military force.