The United States, despite earlier statements to the contrary, has not begun detailed explorations with the Soviet Union about President Leonid I. Brezhnev's proposal on nuclear arms in Europe, the State Department said yesterday.

The reversal of earlier statements was in the form of a clarification of remarks that had been made by a senior State Department official in a briefing for reporters late Friday. The official, who did not permit use of his name, said at that time that several detailed questions about the Brezhnev proposal had been asked of Moscow through Soviet Ambassador Anatoliy F. Dobrynin, but that answers had not been received.

A press statement distributed yesterday said the senior official had been referring to "general discussions" of the Brezhnev proposals. "We have not had detailed conversations with the Soviets" about the matter, the statement said.

According to the State Department, the United States "will consider the matter of seeking systematic clarification from the Soviets" when the United States and its European allies have completed their study of the Brezhnev proposals.

Brezhnev proposed in an Oct. 6 address in East Berlin that the United States and its allies abandon proposals for deployment of longer-range nuclear missiles in Western Europe, and suggested that the Soviet Union would reduce its European missile forces in return.

Officials of the Soviet embassy also said yesterday that, contrary to the earlier reports, Secretary of State Cyrus R. Vance had not begun exploration of the Brezhnev offer in his talks with Dobrynin.