For the first time in 35 years, the Soviet Union has turned off its 2,000 jamming transmitters and allowed Radio Liberty and Radio Free Europe to broadcast news of internal Soviet developments freely into its territory, officials of the U.S. broadcasting operations said yesterday.

Members of the Board for International Broadcasting (BIB), which oversees the two radio operations, hailed the decision as a "historic event" and linked it to Soviet President Mikhail Gorbachev's scheduled meeting in New York next week with President Reagan and President-elect George Bush and to the Soviet desire to host a human rights conference in 1991.

"We think that this is a very significant move by the Soviet Union," said board Chairman Malcolm S. Forbes Jr. "It's the first time in history that they're going to allow those broadcasts to go in unimpeded, unhindered."

Forbes said the hints of a change in the longstanding Soviet refusal even to consider an end to jamming came in September during a meeting in Moscow of Soviet and U.S. officials and news media representatives.

But he and other board members who spoke at a news conference yesterday said the signals then were "very mixed" and "mostly negative." Forbes indicated that they were surprised by the change.

As of late yesterday, BIB officials said they were unaware of any official Soviet announcement of a decision to stop the jamming.

Forbes said he thought it was "more than a coincidence" that the change was made just before Gorbachev's New York visit and his planned meeting with Bush there next Wednesday.

In addition, the United States in mid-November presented the Soviet Union with a new Allied position on the Soviet proposal to host a human rights conference in Moscow in 1991. The U.S. position shifted from "maybe" to an agreement to attend, provided the Soviets met a number of conditions, including an end to jamming of Radio Free Europe and Radio Liberty broadcasts.

Moscow has long regarded the two U.S.-run radio stations as "ideological instruments" used by the United States to undermine "the internal stability and security of the Soviet Union," as a former Soviet Foreign Ministry spokesman described Radio Liberty in May 1987.

Board officials said jamming of Radio Free Europe-Radio Liberty broadcasts into the Soviet Union and Afghanistan stopped at 9 p.m. Tuesday. Jamming of broadcasts from the KOL Israel and West German Deutche Welle radio stations also ceased. But they said jamming of Radio Free Europe broadcasts into Czechoslovakia and Bulgaria continued unabated yesterday.

They speculated that those two East European nations, whose leadership has been unenthusiastic about Gorbachev's new program of glasnost, or openness, would eventually have to end their jamming, too.

Radio Free Europe and Radio Liberty, once CIA-operated stations but now funded by Congress and run by a presidentially appointed board, have been broadcasting news about domestic Soviet events into the Soviet Union since the day after Joseph Stalin died on March 5, 1953.

Since that time, they have been jammed "regularly, day and night," according to Board Vice Chairman Ben J. Wattenberg.

While Radio Liberty broadcasts to the Soviet Union, its sister station, Radio Free Europe, concentrates on Eastern Europe, except East Germany, and the three Soviet Baltic states, which the United States has never formally recognized as part of the Soviet Union.

The two stations, broadcasting in 23 languages, had a budget of $219 million in fiscal 1988.

Both Forbes and Wattenberg speculated that the Soviets had probably come to realize that the estimated $750 million to $1.2 billion they spend annually on jamming was largely a waste of money because it had become "very, very difficult" to stop foreign broadcasts from reaching the Soviet people, particularly in the countryside.

Because of improving technology, said Wattenberg, "it's getting very, very hard to stop messages from getting anywhere in the world."

The Soviets had already stopped jamming the broadcasts of the British Broadcasting Corp. in January 1987 and the Voice of America in May of that year. Poland ended its jamming of American and European radio stations last January.