Mr. Medvedev on Friday maintained that Russia did not feel obligated to respond to the United States as part of some deal. But he added: “There always is a score in politics. And if our partners hear some of our concerns, we will, of course, be more attentive to theirs.”

Mr. Medvedev and Mr. Obama are to meet at the United Nations in New York next week.

Russian officials did indicate that they would withdraw a proposal to base short-range missiles on Russia’s western border, in Kaliningrad, though American officials had not seemed very worried about that Russian plan.

What else Russia might do to respond was a topic of speculation in both Washington and Moscow on Friday. One issue was whether the Kremlin, after more closely examining the new Obama antimissile plan, would voice new protests about it.

Mr. Obama ordered the development of a system that would deploy smaller SM-3 missile interceptors in 2011, at first on ships, later on land in Europe. They are aimed mostly at short- and medium-range Iranian missiles. At least as currently designed, they are not capable of destroying Russia’s intercontinental missiles, though they are expected to be eventually upgraded, Obama administration officials said.

The Obama plan calls for dozens and eventually possibly even hundreds of the smaller interceptors, not just the 10 larger ones included in Mr. Bush’s plan.

Pavel Y. Felgenhauer, a military analyst who writes a column for Novaya Gazeta, an opposition newspaper in Moscow, said he doubted that the Kremlin would be able to complain about the new plan. Mr. Felgenhauer emphasized that the Kremlin had opposed the Bush system because it believed, on the advice of the Russian military, that the system was intended not to bring down Iranian missiles, but to give the United States the potential to make a crippling first strike against Russia.

Also on Friday, in another sign of a warming in relations, NATO called for new cooperation with Moscow, including possibly on antimissile systems.