MOSCOW, OCT. 14 -- Vladimir Slepak, for nearly two decades an outspoken activist and leading figure in the fight for increased Jewish emigration from the Soviet Union, was told today by Soviet officials that he will be allowed to leave for Israel.

Hours after an official called him with the news, Slepak, 59, was still incredulous. "I have the feeling that it is happening not to me but to someone else, and I am looking over my shoulder at the whole thing," he said in an interview.

The resolution of Slepak's 17-year-old fight to emigrate came after Secretary of State George P. Shultz made personal appeals to Moscow on Slepak's behalf and a week before Shultz is to arrive here for talks with senior Soviet officials.

The talks are expected to center on final preparations for a third meeting -- in Washington -- between President Reagan and Soviet leader Mikhail Gorbachev.

Slepak's permission to leave was widely interpreted as a good-will gesture before the summit.

Soviet authorities sent a different signal tonight, however, when a demonstration by Jewish 30 refuseniks, and activist Josef Begun, who recently was told he could emigrate, ended in a clash with police.

The demonstrators had gathered in front of a Soviet television studio that has scheduled a broadcast, Thursday morning, of a conversation by satellite between Soviet legislators and U.S. members of Congress on the issue of human rights.

Minutes after the protest against restriction of emigration began, plainclothesmen cut the cables of American television reporters who had come to the scene. The police jostled the peaceful demonstratators and eventually broke up the protest.

Slepak was aglow at a celebration tonight at a restaurant, surrounded by nearly 100 friends and his wife Maria, who is to leave with him in two to three weeks.

The party was for Ida Nudel, a friend and fellow activist, who is to leave for Israel with American industrialist Armand Hammer Thursday. Nudel, who like Slepak had waited years to leave Moscow, received word that she could go two weeks ago.

Slepak said, however, that the recent resolution of a cluster of cases of Jews long refused permission to leave the U.S.S.R. "is not a solution to our problem. The problem will be solved when anyone who wants to leave can do so."

While the Soviet leadership has indicated its intention to improve its human rights record by allowing emigration to increase four-fold this year, crackdowns against demonstrations and other signs of resistance to the liberal policies of glasnost, or openness, continue.

Slepak was one of the last of the Jews who since the early 1970s have been refused permission to leave. He is a radio technician who lost his job when he first applied to emigrate in 1970. He was denied permission on the grounds that he knew state secrets. In 1975, Slepak joined the Helsinki Watch Group, an unofficial collection of people who monitored Soviet compliance with the Helsinki human rights accords.

In 1978, when Jewish emigration was climbing to a peak, Slepak and his wife and sons demonstrated for permission to emigrate. Slepak was tried for "hooliganism" and sentenced to five years in internal exile, near the Mongolian border.

Since his return to Moscow, Slepak has been heavily involved in protests calling for the right of emigration. As a result, he has been in and out of detention and was held by Soviet police for several hours last month.

"This is a good time to press for human rights," Slepak said tonight. "Gorbachev needs and wants help. He needs moral help, he needs new technology and he needs credits. The U.S. can give these things, and that's why it's a good time for the U.S. to press on human rights."

Slepak's children have already emigrated to the United States. His son Alexander, 35, lives in Philadelphia and Leonid, 28, lives in Jersey City.