BONN, JAN. 11 -- Police today arrested a West German woman who authorities said is "strongly suspected" of having planted the terrorist bomb that exploded in a West Berlin discotheque in 1986 and killed three persons, including two American servicemen.

Following the bombing of the La Belle discotheque on April 5, 1986, the United States staged a retaliatory air raid against Libya after the Reagan administration said it had "conclusive" evidence Libya had ordered the attack.

But West German sources familiar with the case said the new clues that led to the woman's arrest have strengthened the hypothesis that the discotheque bombing was staged with Syrian rather than Libyan backing.

The arrested woman, Christine Endrigkeit, is suspected of having planted the bomb on the orders of a convicted Arab terrorist who has been linked by a court to Syrian officials in another West Berlin terrorist bombing, judicial authorities said.

Investigators now find a possible Syrian connection "more interesting" than before in light of the evidence implicating Endrigkeit, a West German source, who spoke on condition that he not be identified, said.

Endrigkeit was arrested at 2:40 a.m. in the northern port city of Luebeck on suspicion of murder, judicial spokesmen said. Police grabbed her after receiving a tip less than 12 hours after West Berlin authorities announced that she was wanted in the case and distributed a photograph of her.

Endrigkeit is "strongly suspected" of planting the bomb at the discotheque because of evidence from documents and testimony of witnesses, West Berlin judicial spokesman Volker Kaehne said.

There is a "suspicion," based on the same sources, that Endrigkeit planted the bomb on orders of convicted terrorist Ahmed Nawaf Mansour Hasi, Kaehne said.

Hasi, who is of Palestinian origin and carries Jordanian identity papers, is serving a 14-year term for having helped plant a bomb that injured seven people at the German-Arab Friendship Society in West Berlin a week before the discotheque bombing.

Kaehne said that the only evidence of a Syrian or Libyan connection in the La Belle case was what already had been made public about Hasi in trial for the German-Arab social club bombing.

In that trial, in November 1986, the court said that it was convinced that some Syrian officials helped to plan the attack and provided the explosives for it.

Hasi and two other Arabs went to Libya in July 1985 in hope of obtaining backing for a guerrilla group, according to testimony. They got $5,000 but were dissatisfied with what they saw as only token support and turned to Syria, it said.

The other two Arabs were Farouk Salameh, who was convicted as Hasi's accomplice in the German-Arab club bombing, and Hasi's brother, Nezar Hindawi.

Hindawi is serving a 45-year-sentence in Britain for plotting an attempt to blow up an Israeli airliner the same month as the discotheque bombing. Evidence at the West Berlin and London trials implicated Lt. Col. Haithem Saeed, identified as a senior Syrian Air Force intelligence officer, as playing a leading role in planning both attacks.

According to testimony in West Berlin, Hasi got the bomb used in the German-Arab club attack from Saeed at the Syrian Embassy in East Berlin.

Endrigkeit was flown to West Berlin this evening, and investigators planned to begin interrogating her there on Tuesday.

Kaehne and other sources were cautious about prospects that the arrest would break open the La Belle case. "I do not want to produce too much hope," Kaehne said.

A source familiar with the case said that it would be "a difficult thing to pin her down."

The U.S. government believes that it would be impossible, for legal reasons, to request Endrigkeit's extradition to the United States, a U.S. official said. He noted that the bombing did not take place in a U.S. facility, and that West Berlin has a special legal status based on postwar agreements with the Soviet Union, Britain and France.