Ahmed Nawaf Mansour Hasi, a Palestinian who was detained in the April 5 discotheque bombing in West Berlin that led to U.S. air strikes on Libya, said he carried out a similar terrorist attack a week earlier at the German-Arab Friendship Society, West Berlin judiciary officials said today.

Police sources said Hasi and his brother, Nezar Hindawi, plotted the Easter explosion that destroyed the German-Arab office and injured seven persons after a heated argument with moderate members who defended the "apolitical character" of the group. Hindawi is now in London police custody on charges of trying to blow up an El Al jetliner carrying 400 passengers by planting a bomb in the suitcase of an unsuspecting girlfriend before she boarded the plane.

It was the first confirmation that the two brothers had worked in tandem to organize acts of terror in Europe. Hindawi visited his brother in West Berlin last February, and investigators suspect that he could have obtained there the explosives used to make the suitcase bomb that security guards discovered at Heathrow Airport.

Investigators are now trying to compare the nature of the volatile materials found in London with traces from the two blasts in West Berlin. West German police officials said no remnants of the bombs were found, but their explosive impact was nearly identical.

Two other Arabs, named as Farouk Salameh and Fayez Sahawneh, were arrested May 1 in West Berlin and had pleaded guilty to serving as accomplices with the two brothers in the bombing of the German-Arab office, police said.

But West Berlin police chief Manfred Ganschow said, "There are very, very few indications that they might also be involved in the La Belle discotheque bombing."

Hasi also has continued to deny that he played any role in the explosion that killed two persons, including an American serviceman, and injured 230. But security sources said there is sufficient evidence, including sketches of intended terror targets in the city, to keep him in investigative custody.

Volker Kaehne, a city justice department spokesman, said in an interview that police had established that Hasi and Salameh had secured explosives from "an Arab office in East Berlin" and made repeated trips transporting them to the West for use in the attack. Other officials said the description referred to the Libyan People's Bureau, or embassy, in East Berlin.

[The Associated Press reported yesterday that Hasi and Salameh claimed they got the explosives for that attack from the Syrian Embassy in East Berlin, according to federal police officials who spoke to the AP on condition of anonymity.]

West Berlin police have ascertained certain Libyan connections, including at least one visit to Tripoli by Hasi since he moved to West Berlin in 1975. But security officials said that possible terror links to Syria also are being closely scrutinized.

West German police have been working with the assistance of allied intelligence services to determine whether Hasi and his brother may have received training and direction in Damascus. One security source said the investigation of the La Belle bombing was "now looking more than it did earlier toward Syria."

West German police officials would not comment on the possible Syrian links in the case, citing the need to avoid jeopardizing emerging leads and potential arrests. But one security official predicted that a major development in the investigation was expected to be confirmed "in the next few days."

Klaus Mueller, political chief of the West Berlin public prosecutor's office, said that West Germany was seeking close cooperation with East German authorities in curtailing the risks of terrorism emanating from Arab offices in East Berlin.