MOSCOW — Russia is to withdraw from Europe’s key arms control treaty in response to America’s plans to install missile defense systems in Eastern Europe, President Putin announced yesterday.

In his annual state of the nation address, the Russian president accused the American government of a plot to build up its military forces on Russia’s western borders.

“Our partners are conducting themselves incorrectly to say the least, gaining one-sided advances,” he said.

“They are using the complicated situation to expand military bases near our borders. Moreover, they plan to locate elements of a missile defense system in the Czech Republic and Poland.”

The Conventional Forces in Europe Treaty, which was signed in the dying months of the Cold War, is regarded as the cornerstone of stability in Europe. It places limits on the number of conventional weapons and foreign forces that can be deployed among member nations.

Already strained relations between the two Cold War superpowers deteriorated markedly when the Pentagon announced plans to place 10 interceptor missiles in Poland and a radar system in the Czech Republic.

Moscow has rejected Washington’s pleas that the shield was meant to defend Europe from a rogue missile attack by Iran, claiming that Russia’s nuclear arsenal was the target.

American attempts to mollify the Kremlin by inviting Russia to inspect the proposed sites and co-operate in the project have been rebuffed.

In the first indication that America was losing patience with Moscow’s intransigence on the issue, Secretary of State Rice yesterday described Russia’s fears as “ludicrous.”

“The Russians have thousands of warheads,” she told a press conference in Oslo prior to a NATO meeting.