The Soviet Union has stepped up its efforts in the past two years to exploit the U.S. nuclear freeze movement, but by no means plays a leading role in it, the FBI said in a report made public yesterday.

"Based on information available to us, we do not believe the Soviets have achieved a dominant role in the U.S. peace and nuclear freeze movements, or that they directly control or manipulate the movement," the FBI intelligence division concluded.

At the same time, the bureau said, Soviet agents have achieved some success in creating an impression that the Soviet Union is more interested than the United States in disarmament.

The report conflicted with President Reagan's oft-stated suggestion that the freeze movement was "inspired" by communist agents, even though it did say that the Soviets have been striving to capitalize on it.

The FBI report, dated March, 1983, and entitled "Soviet Active Measures Relating to the U.S. Peace Movement," was prepared at the request of the House Intelligence Committee. A declassified version was released by Rep. C.W. Bill Young (R-Fla.).

A major portion of the study was devoted to last June's peace demonstration in New York City that drew nearly a million people together in protest against nuclear weapons.

The FBI said that "based on available information, we do not believe that the Soviet Union and its proxies directly controlled the proceedings . . . nor were they responsible for the large turnout at the rally.

"The overwhelming majority . . .were members of independent peace and civic organizations, and they attended the rally as an expression of legitimate concerns about nuclear weapons," the FBI said.

The report added, however, that "Soviet-controlled organizations participated at the highest levels of the June 12 Committee" that planned the rally and exerted pressure to focus the rally primarily on what the committee called U.S. responsibility for the arms race.

The FBI said the "pro-Soviet" U.S. Peace Council, founded in 1979 with U.S. Communist Party members in "key leadership positions," played an important role in the planning and organization of the June 12 demonstration and had at least one seat on the June 12 executive committee.

During committee meetings, the report said, U.S. Peace Council-Communist Party representatives "actively campaigned to direct the focus of the demonstration exclusively against U.S. weapons systems," and the committee largely agreed, characterizing the U.S. government as "the least willing to stop its nuclear insanity."

"The committee's rationale was that the Soviet Union supports several committee proposals, including a bilateral nuclear freeze," the report said.

The FBI said the Soviet KGB has also been taking part in the campaign by "attempting to develop contacts with religious figures in the United States," and by collecting personal and biographic information on several peace activists to determine if any of them might be "vulnerable to recruitment operations."

The report, however, did not support Reagan's contention in a speech last October when he said the freeze movement was "inspired not by the sincere, honest people who want peace, but by some who want the weakening of America and so are manipulating many honest and sincere people."