Richard Pipes, the author of a monumental, sharply polemical series of historical works on Russia, the Russian Revolution and the Bolshevik regime, and a top adviser to the Reagan administration on Soviet and Eastern European policy, died on Thursday at a nursing home near his home in Cambridge, Mass. He was 94.

His son Daniel confirmed the death.

Professor Pipes, who spent his entire academic career at Harvard, took his place in the front rank of Russian historians with the publication of “Russia Under the Old Regime” in 1974. But he achieved much wider renown as a public intellectual deeply skeptical about the American policy of détente with the Soviet Union.

In 1976, he led a group of military and foreign-policy experts, known as Team B, in an ultimately pessimistic analysis of the Soviet Union’s military strategy and foreign policy and the threats they posed to the United States.

The group’s report, commissioned by the Central Intelligence Agency as a counterweight to an analysis that had been generated by the C.I.A.’s own experts — Team A — helped galvanize conservative opposition to arms-control talks and accommodation with the Soviet Union. And it set the stage for Ronald Reagan’s policy of challenging Soviet foreign policy and seeking to undermine its hold over Eastern Europe.