WASHINGTON — A pair of nuclear-powered Russian attack submarines has been patrolling off the eastern seaboard of the United States in recent days, a rare mission that has raised concerns inside the Pentagon and intelligence agencies about a more assertive stance by the Russian military.

The episode has echoes of the cold war era, when the United States and the Soviet Union regularly parked submarines off each other’s coasts to steal military secrets, track the movements of their underwater fleets — and be poised for war.

But the collapse of the Soviet Union all but eliminated the ability of the Russian Navy to operate far from home ports, making the current submarine patrols thousands of miles from Russia more surprising for military officials and defense policy experts. “I don’t think they’ve put two first-line nuclear subs off the U.S. coast in about 15 years,” said Norman Polmar, a naval historian and submarine warfare expert.

The submarines are of the Akula class, a counterpart to the Los Angeles class attack subs of the United States Navy, and not one of the larger submarines that can launch intercontinental nuclear missiles.

According to Defense Department officials, one of the Russian submarines remained in international waters on Tuesday about 200 miles off the coast of the United States. The location of the second remained unclear. One senior official said the second submarine traveled south in recent days toward Cuba, while another senior official with access to reports on the surveillance mission said it had sailed away in a northerly direction. The Pentagon and intelligence officials spoke anonymously to describe the effort to track the Russian submarines, which has not been publicly announced.

President Obama spoke by telephone with President Dmitri A. Medvedev of Russia on Tuesday, but it was not clear whether the subject of the submarines came up, although another source of friction between the two countries did. Mr. Medvedev called Mr. Obama to wish him a happy birthday and the White House said the president used the opportunity to urge Russia to work through diplomatic channels to resolve rising tensions with Georgia.

The submarine patrols come as Moscow tries to shake off the embarrassment of the latest failed test of the Bulava missile, a long-range weapon that was test fired from a submarine in the Arctic on July 15. The failed missile test was the sixth since 2005, and some experts see Russia’s assertiveness elsewhere as a gambit by the military to prove its continued relevance.
“It’s the military trying to demonstrate that they are still a player in Russian political and economic matters,” Mr. Polmar said.