Soviet authorities have introduced new restrictions on Jews seeking to emigrate, according to well-informed sources.

Activists now say that Soviet authorities in the major Ukrainian city of Kharkov, considered by many Jews here to be a bellwether of Soviet emigration policies, are refusing to reconsider the case of any Jew who has once been denied permission to emigrate.

The new practice of barring reapplication represents a stark departure from longstanding Soviet policy of allowing so-called refusedniks -- Jews prevented from emigrating chiefly because they allegedly possess state secrets -- to reapply for a visa every six months. In many instances, repeat applicants eventually have been allowed to leave, although some have had to wait years.

The activists said in recent interviews that anyone turned down for emigration now must sign a declaration asserting he has been "warned that I have been refused [emigration permission], that my refusal is final, and that I have no right to reapply. I must get a job in a month." i

The Kharkov activists, Yevgeny Chudnovsky, David Soloveichik, Yuri Tarnopolsky and Alexander Paritsky, estimated that some 500 families there have been refused exit visas in the past year and only a handful allowed to leave. The men say they believe the crackdown in Kharkov, which survived as a traditional cultural center for Ukrainian Jews until after World War II despite Stalinist repressions and a Nazi massacre, may be motivated in part by rising Soviet fears of a "brain drain."

Western analysts of the mass exodus of more than 200,000 Soviet Jews from the land of their birth in the past decade say the emigres are drawn largely from better-educated sectors of Soviet society.

Yet recent figures available in the West also show that the Soviets have steadily shut the emigration tap this year, a probable reflection of the chill on East-West relations in the aftermath of the Afghanistan invasion. While more than 50,000 Jews were allowed to leave last year, a record, so far in 1980, about 15,000 have been allowed to leave during the first eight months.

Part of the sharp decline is attributable to the Moscow Olympics, when visa officials were processing tourists. But early reports for September indicate that not more than 1,500 are likely to be allowed to leave this month, matching the pre-Olympic record low of 1,500 for June.

"There is no incentive for them to increase the amounts," one activist said.

So far, Moscow activists say, no similar ban on reapplication for visas has been imposed by regional emigration officials elsewhere in the country. Yet Kharkov and Odessa, another major Ukrainian city, were the first places last year to begin systematically using a much tighter definition of family relations to allow Jews to qualify for family reunification board.

Prior to that time, the Soviets frequently allowed relatives as distant as cousins and nephews and nieces to emigrate. That has largely been ended, with the officials insisting that only parents, children, siblings and spouses can be considered under the reunifications provisions of the 1975 Helskinki act, which spurred Jewish emigration.

Some Westerners had speculated that the Soviets, faced with the Madrid conference in November to review compliance with the Helsinki accords, might suddenly allow a sharp rise in emigration to improve its image and standing among the 34 other signatory powers. Yet that seems unlikely now in the view of observers here.