Twelve European nations decided today to impose specific restrictions on the size and activities of Libyan diplomatic missions, or "People's Bureaus," to show displeasure with the regime of Col. Muammar Qaddafi for its involvement in terrorist acts.

The decision, taken by foreign ministers of the European Community states, was intended to answer American appeals for coordinated punitive actions against Tripoli by the allies and to forestall the threat of further U.S. military strikes, diplomats said. It built on a general agreement on diplomatic sanctions approved April 14 at a community meeting in The Hague.

[In Washington, the Reagan administration welcomed the accord as "a clear message to Qaddafi that the Europeans, like the United States, will not tolerate this scourge," said State Department spokesman Bernard Kalb.]

The ministers refrained from shutting down the People's Bureaus altogether, as Britain's Geoffrey Howe had previously urged, or taking steps to pressure Qaddafi by hurting the Libyan economy. West Germany, in particular, has strongly rejected economic sanctions, saying they do not work.

The growing anxiety that new American bombing raids on Libya would unleash a fresh wave of terrorist reprisals heightened a sense of urgency among the ministers to reach a consensus on a package of measures that would show they were actively committed to halting a continuing cycle of violence.

Today's accord calls for Libyan diplomats and consular representatives to be reduced to the minimum required to handle their official business. European embassies in Tripoli will be cut similarly.

Libyan diplomats in Europe also will be restricted to the capital or city in which they serve and will be prohibited from traveling without special permission. The EC states asked a group of experts to explore other ways in which diplomatic privileges could be curtailed without violating international conventions.

Visas to Libyan nationals will also be reduced in number, and Libyan expatriates who work in Europe in the private sector will be subjected to much closer scrutiny by authorities.

The 12 also agreed that any Libyan expelled from one state also will be persona non grata in the rest of the community.

"We have proved the community is determined to fight against international terrorism," said West Germany's Hans-Dietrich Genscher. "Our decision is directed against Libya, but it is also meant as a warning to other states which may act in a similar manner."

Several diplomats remarked that the European failure to take strong action against Libya in the aftermath of the airport attacks in Vienna and Rome last December probably contributed to American frustration that led to Tuesday's bombing raid on Tripoli and Benghazi.

The American planes took off from their British bases only hours after last Monday's EC meeting in The Hague, the second on the current Libyan crisis, when ministers singled out Libya as "clearly implicated in supporting terrorism" and approved a general sanctions package. That action followed the bombing of a West Berlin discotheque on April 5 in which a U.S. soldier and a Turkish woman were killed and more than 200 persons injured. The United States said it had evidence proving Libyan involvement.

Today's meeting opened with Greece sharply opposed to broader diplomatic restrictions. Last week, Greece emerged as the most outspoken critic of the U.S. bombing and its European affairs minister, Theodore Pangalos, reportedly argued that the EC states should not allow themselves to be pushed into taking drastic steps by American military action.

But Howe and Genscher contended that the European countries needed to adopt far-reaching measures to prove to the public and the United States that allied governments were serious about preventing a military escalation of the conflict in the Mediterranean. "We had to show ourselves able to take effective, collective action," Howe reporters later. "It was crucial for the credibility of the community."

Dutch Foreign Minister Hans van den Broeck, who chaired the meeting, suggested the restrictions might be extended to other states, saying the European action "should be seen as a signal to other countries possibly involved in terrorist activities."

At the same time, he noted that the Europeans wanted to establish better cooperation with Arab countries so a more useful dialogue on political and security issues could be developed.