Israeli authorities, in a reversal of a previous hands-off policy, today acted vigorously to head off a strike by shop-keepers in Arab East Jerusalem and in the occupied West Bank by threatening reprisals against merchants who refuse to open their stores.

All stores in East Jerusalem were opened by late morning and business had returned to normal. In most West Bank cities, stores were also open by 11 a.m. and only in Nablus, the area's largest town was the strike maintained all day.

The strike had been called by the Arab National Guidance Committee in the West Bank to protest Israel's refusal to allow the return of three Palestinian leaders from the Hebron area who were expelled to Lebanon 10 days ago.

During the first years of Israel's occupation of the West Bank, then defense minister Moshe Dayan followed a policy of breaking storekeepers' strikes.

As the strikes became less frequent, however, Dayan decided that Israel would not intervene in strikes or other forms of protest as long as public order was maintained.

The present minister of defense, Ezar Weizman, followed the same hands-off policy until today. In recent weeks strikes have crippled trade in East Jerusalem and several West Bank towns, especially Ramallah.

Senior Israeli officials said the policy reversal stemmed from concern that if the Israeli government did not act now, the West Bank population would view this as an abdication of its authority in favor of the Palestine Liberation Organization and the Committee of National Guidance, a West Bank Arab organization. The Israelis were particularly sensitive to Arab protest moves in Jerusalem, where Israel intends to celebrate the 13th anniversary of the unification of the city on Wednesday.

Shops began to open in Jerusalem this morning when Israeli soldiers arrived with writs signed by the Israeli Army area commander ordering Arab merchants to open their stores. Few of the writs were served, however, and no shop was forcibly opened by the soldiers.

Jerusalem Mayor Teddy Kollek, who had insisted that the new policy be carried out of the Israeli Army rather than by municipal authorities, demonstrated the return to "business as usual" by purchasing a flower vase and carpet for his office in the bazaar of Jerusalem's Old City.