Despite new evidence that Syria may have been involved, the Reagan administration yesterday reaffirmed its earlier assessment that Libya was primarily responsible for the bombing of a West Berlin nightclub that provoked the April 1986 U.S. military raid on Libya.

The evidence pointing to Syrian complicity in the attack on the discotheque has reopened the issue of the extent of past Syrian involvement in anti-U.S. terrorism, just when the administration has moved toward improving relations with Damascus, seriously strained by British evidence of a Syrian role in the attempted bombing of an El Al airliner with 230 Americans aboard in London in April 1986.

Although U.S. economic sanctions against Syria remain in force, and the U.S. lists Syria as sup- porting state terrorism, Washington has sent U.S. Ambassador William L. Eagleton Jr. back to Damascus.

State Department spokeswoman Phyllis Oakley said the United States had "clear, and in our view, unequivocal evidence of Libyan culpability" in the April 5, 1986, bombing of the La Belle Discotheque in which two U.S. servicemen and a Turkish woman were killed and 204 others were injured.

"Nothing learned since . . . has led us to question Libyan involvement," she said. "The possibility" that another country may have also been involved, she added, "in no way contradicts the evidence about Libya."

Oakley said the United States has "seen no evidence that Libya has abandoned support of international terrorism, subversion and aggression," or that Libyan leader Moammar Gadhafi's goals have changed. She said the administration will continue to promote Gadhafi's isolation, "diplomatically and economically, in order to limit his ability to cause harm."

The administration has just extended economic sanctions, imposed against Libya a year ago, for another year.

On his plane while flying to Ottawa yesterday, Secretary of State George P. Shultz bristled when asked by reporters whether the United States had "trumped up" charges against Libya to justify the air raid on Tripoli, the Libyan

capital, and Gadhafi's headquar- ters.

"I think it's clear enough from the evidence that Libya was directly involved in that {nightclub} bombing," he said. "It was a very direct Libyan complicity."

The possible Syrian connection to Christine Gabriele Endrigkeit, the West German woman who was arrested Sunday as a suspect in

the discotheque bombing, "doesn't change the Libya fact at all,"

Shultz said. "That doesn't mean that there can't be others with other countries involved or in the background."

The U.S. assessment of Libya's primary role in the La Belle bombing was based on U.S. intelligence intercepts of radio communica- tions between the Libyan People's Bureau in East Berlin and Trip- oli.

Oakley said the United States was watching the West German investigation of Endrigkeit "closely" and "with special interest."

"We will be following the Berlin investigation closely and with special interest in the possibility

that another government in addi- tion to the government of Libya may have been involved," Oakley said.

She refused to speculate on any further action the administration might take if the West German investigation shows Syria was also involved in the La Belle nightclub bombing.

The State Department spokeswoman also said the administration would not seek to have Endrigkeit extradicted to the United States because the legislation allowing this in the case of terrorist acts against U.S. citizens abroad had not yet taken effect at the time of the La Belle bombing.Washington Post correspondent Herbert H. Denton contributed to this report.