The Reagan administration bombed Muammar Qaddafi's personal compound -- the nerve center of his regime -- as one of its primary targets in Monday's raid after U.S. intelligence had traced key terrorist communications and planning to the complex, which is called the Bab Azizzia, or "Splendid Gate," barracks, according to informed sources.

The barracks complex was described yesterday as the operational headquarters of the Libyan military and terrorist organization, housing communications systems, command staff, the official government radio station and a contingent of Qaddafi's elite security troops deemed most loyal to his revolutionary dictatorship.

Qaddafi maintains his residence in the barracks, living in a Bedouin-style tent erected in a courtyard of the complex, but the Libyan leader seldom stays more than one night at any of his several residences as a precaution against assassination by internal dissident elements or external enemies, according to sources.

The targeting of Qaddafi's personal compound raised concerns in the National Security Council that the military strike -- coming as it did in the midst of an administration covert action to undermine Qaddafi's rule -- might violate an executive order prohibiting any attempt by U.S. officials to assassinate a foreign leader.

After investigating this question, sources said, administration legal counselors advised that the strike could be justified as a self-defensive and preemptive military attack. Any deaths, the legal analysis held -- even the death of the head of state -- could not be considered political assassination.

[Libyan reports said yesterday that one of Qaddafi's children, an adopted girl, had been killed in the barracks and that his two youngest sons were seriously injured.]

One high-level official said yesterday that the three key messages cited by President Reagan in his Monday night address to the nation could not be traced unequivocally to the "Splendid Gate" headquarters. Reagan pointed to those specific messages as "irrefutable" evidence that the Libyan regime ordered the terrorist bombing of a West Berlin nightclub 11 days ago that killed two people and wounded 230.

Another well-placed source, however, said one of the three messages had been traced to Qaddafi's command and control center at the Bab Azizzia barracks.

One source yesterday said that new intelligence reports show that Libya is continuing, if not actually stepping up, planning for terrorist attacks against U.S. targets in the Middle East and Europe. The source did not interpret this as an ominous new development, but rather as an indication that the U.S. raid had not fundamentally changed Libyan plans or attitudes.

The administration had by Monday accumulated substantial intelligence on additional Libyan terrorist plans, according to one source. This source described the intelligence as showing "an orchestrated, worldwide, centrally directed campaign of terror directed through the Libyan diplomatic channels and missions specifically targeting Americans."

Several other officials said yesterday afternoon that it was too early to determine if Monday's bombing raids at five key Libyan targets were generating more terrorist plans or deterring them. "That part of the evaluation is still ongoing," one source said.

Since the Gulf of Sidra naval exercise three weeks ago, intelligence reports show that the terrorist plans were "the clear policy of Tripoli" and not just passive support or occasional expressions of sympathy with radical Arabs, according to this source.

Vernon A. Walters, the U.S. ambassador to the United Nations, yesterday said "the United States also has compelling evidence of Libyan involvement in other planned attacks," including a late March incident in which police in Istanbul arrested two people claiming to be Libyan-sponsored terrorists planning attacks against the U.S. targets in Turkey.

Earlier this month, Walters said, "France expelled two Fatah Force 17 members recruited by Libya to conduct another operation against the United States in Paris." Fatah Force 17 is the security force under the control of Palestine Liberation Organization leader Yasser Arafat.

Also, Walters said, "on April 6, a Libyan plot to attack the U.S. Embassy in Beirut resulted in a near miss by a 107-mm rocket which exploded on launch."

The Libyan People's Bureau in Vienna was planning a terrorist attack against an unknown target there to take place on Thursday this week, Walters told the U.N. Security Council.

Stressing the scope of the Libyan plans, Walters also said that Libya has called "for terrorist action and acts of aggression and subversion against its neighbors, against European countries and against places as far away as Northern Ireland, the Philippines and Central America."

"More than 40 so-called Libyan diplomats have been expelled from Western Europe since 1983 for involvement in criminal activities," Walters said.

The decision by the United States to attack Qaddafi's Splendid Gate barracks was considered significant by a number of sources. U.S. intelligence reports often referred to the well-fortified barracks as "the presidential villa." On May 8, 1984, when a group rebels attempted to overthrow Qaddafi, they reportedly attacked the barracks compound, which is surrounded by a 15-foot wall and guarded by Soviet-built tanks.

A top secret "vulnerability assessment" done by the Central Intelligence Agency and other U.S. intelligence agencies in June 1984 clearly anticipated more coup attempts and said, "disaffected elements in the Libyan military could be spurred to assassination attempts or to cooperate with the exiles against Qaddafi."

In fact, sources said, there were three more coup attempts in 1985, at least two of them resulting in the executions of dozens of Libyan army officers charged with complicity in the plots.