For more than a decade, Libya's embassies have been called People's Bureaus as a sign of Muammar Qaddafi's determination to break the mold of traditional diplomacy and transform them into outposts for spreading his ideas of revolution beyond the shores of North Africa.

According to the Reagan administration, Qaddafi's pursuit of his revolutionary vision has made the People's Bureaus the nerve centers from which his agents, operating under the cover of diplomatic immunity, have helped spin a web of international terrorism across Western Europe and the Middle East.

When President Reagan ordered U.S. warplanes to strike Libya last week, he was responding to what administration officials contend was undeniable evidence that the People's Bureau in East Berlin arranged the April 5 bombing of a West Berlin nightclub, where an American soldier and a Turkish woman were killed.

It was not the first time a People's Bureau has been linked to an act of terrorism. Two years ago, a gunman inside the London People's Bureau sprayed machine-gun fire on a crowd of protesters, killing a policewoman and wounding 11 Libyan student dissidents. The incident led to the severing of diplomatic ties between Britain and Libya.

Such activities have caused the Reagan administration to call repeatedly for its allies to close the People's Bureaus in their capitals as a means of inhibiting Qaddafi's support of terrorism. There are roughly 100 People's Bureaus around the world, including 27 in Europe and eight in Latin America. The one here was closed by the administration in 1981, although Libya still has a mission at the United Nations.

West European governments, while privately acknowledging that Washington's charges are correct, have been unwilling to close the bureaus because of trade ties with Libya or a belief that isolating Qaddafi diplomatically will make him more dangerous. Instead, they have resorted to limited measures such as the recent expulsion of some Libyan diplomats from France and West Germany.

As a result, U.S. diplomatic and intelligence officials charge, Qaddafi remains relatively unfettered in his ability to use the People's Bureaus to maintain contact with terrorist groups in various countries and to supply them with cash and weapons carried in diplomatic pouches and baggage.

According to U.S. officials, this type of activity has increased markedly in the past year as the nature of Libyan involvement in terrorism has changed and expanded.

For many years, the officials said, Qaddafi's main involvement in terrorism was contributing money from Libya's oil revenues to foreign groups such as the Palestine Liberation Organization and the Irish Republican Army. While his agents were active in other countries, they concentrated on intimidating and, in some cases, assassinating dissident Libyan exiles.

About a year ago, the officials continued, the Libyans began broadening their overseas activities by working closely with surrogate terrorist groups such as the Palestinian faction led by Abu Nidal in the financing and planning of major terrorism operations. Before the Berlin nightclub bombing, the United States contends, Libyan agents were involved in the hijacking of an Egyptian airliner to Malta last November and attacks on the Rome and Vienna airports in late December.

In each case, U.S. officials assert, People's Bureaus were involved. Their role stems from Qaddafi's efforts, instituted shortly after he seized power in 1969, to make them an extension of the Revolutionary Committees that are his base of popular support in Libya.

The committees, headed by his second in command, Maj. Abdul Salaam Jalloud, draw their members from young, fanatically loyal adherents to Qaddafi's precepts. Large numbers of them have been assigned to People's Bureaus where, U.S. officials say, their job is to wage secret war against Libyan dissidents and increasingly to engage in more wide-ranging terrorism, either directly or in collaboration with surrogates.