BRUSSELS, JUNE 29 -- The European Community is expected to drop a ban on high-level diplomatic meetings with Syrian officials next month following an apparent crackdown by Damascus on the Abu Nidal terrorist group, diplomats said today at the start of a two-day community summit.

The 12-nation group probably will revoke the seven-month-old sanction at a meeting of foreign ministers on July 13 in Copenhagen, British and other European diplomats said.

Britain originally sought the ban because of evidence linking Syrian officials to a plot to put a bomb on an Israeli airliner at London's Heathrow Airport in April 1986 and had been the only country still supporting the sanction, European diplomats said.

But now Britain "would not stand in the way" of the change in policy, a senior British official said. He attributed the shift to evidence in recent weeks that Syria has shut down offices of the Abu Nidal group, one of the Middle East's most active terrorist organizations.

The expected move reflects a gradual thaw in relations between western governments and Syria in recent months following a series of diplomatic ruptures late last year that resulted from evidence that Syrian officials had given support to international terrorists.

President Reagan earlier this month sent a secret letter to Syrian President Hafez Assad offering to improve relations between the two countries and is expected to send a special envoy, possibly U.S. Ambassador Vernon Walters, to Damascus to renew a dialogue.

Officials said the administration had concluded that Syria's record on international terrorism had greatly improved since last fall. The United States withdrew its ambassador to Damascus in October as a protest against Syria's alleged complicity in the attempt to place the bomb on the airliner in London.

West Germany recently sent a new ambassador to Damascus following a delay of several months after a West Berlin court linked a Syrian Air Force intelligence officer to the bombing in March 1986 of a German-Arab cultural society.

Many community members feel that it is particularly important to resume high-level contacts with Syria now because of their interest in promoting a Middle East peace conference and the important role that the Syrians play in Middle East diplomacy, diplomats said. Belgian Foreign Minister Leo Tindemans was unable to visit Damascus in April to discuss a regional peace conference because of the community's ban on such trips.

France and West Germany also would like to improve ties with Syria because Damascus has some influence with kidnapers holding their citizens as hostages in Lebanon.

The Syrian issue was not expected to come up here at the meeting of heads of government and of French President Francois Mitterrand, who is a head of state, diplomats said. The summit was paying little attention to political issues and instead was focusing on how to shore up the community's financial situation, they said.

The ban on high-level contacts with Syria was the most important measure in a package of limited sanctions adopted in London on Nov. 11 by all but one of the community's members. Greece refused to go along with its partners.

The community had agreed that it would not relax the sanctions until Syria took specified steps against terrorism, British officials said.

One such step was the shutting down of Abu Nidal's offices in Syria, and Damascus appears to have complied, the officials said. The Jordan Times reported June 4 that Syria closed Abu Nidal's operations in the Yarmuk refugee camp for Palestinians and ordered members of the group without Syrian passports to leave the country immediately, according to The Associated Press.

Abu Nidal is the nom de guerre of Sabri Banna, a Palestinian radical who broke with the Palestine Liberation Organization because he viewed PLO Chairman Yasser Arafat as too moderate.

A British official emphasized that London would oppose any relaxation of the other sanctions unless Syria prosecuted the officials linked to the airliner plot and there was "sustained and conclusive evidence that support for terrorism has been abandoned."

The other sanctions were an embargo on new arms sales to Syria, increased surveillance of Syrian diplomats and a tightening of security around Syrian Arab Airlines.