Some days back, people were making quips about "the mouse that roared," but the joke is now wearing thin. At today's plenary, Malta took a hammering for blocking the conclusion of the East-West conference on detente in Europe.

At the meeting of 35 participating delegations, the ambassador from the Netherlands called the Maltese government "foolish," "ridiculous" and "stupid." In the corridors, diplomats from East and West and from the neutral nations spoke darkly of "diplomatic terrorism."

Outside the coffee bar of Madrid's Palace of Conferences, where the Conference on Security and Cooperation in Europe has been meeting since November 1980, Maltese Ambassador Evarist Saliba told reporters: "I'm not a sadist spoiling people's holidays. I don't relish my role."

But sympathy was scarce for Malta among diplomats faced with the prospect of enduring Madrid's August heat and unable to bring the conference to a close. For 10 days Malta has been denying the necessary consensus to end Madrid's review of the 1975 Helsinki detente accords.

Dutch Ambassador Bob Croin did not mince his words: "For what reason does Malta hold up this meeting?" Croin, who has attended detente meetings in Geneva, Helsinki and Belgrade continued: "Apparently to get a little more for itself. Malta is behaving foolishly--like a spoiled child insisting on having more sweets and then throwing a tantrum when it does not get them."

Saliba played it low key and replied that Croin was being "emotional." The Maltese ambassador, a fellow veteran of the detente process, was pursuing a well-charted path of Maltese filibustering that has characterized Maltese diplomacy at every other meeting of the security conference.

Earlier this month the conference participants--the United States, Canada and all Europe except Albania--agreed on compromise detente accords that include follow-up meetings on disarmament, human rights and the reunification of divided families.

Malta wants a separate meeting on military security in the Mediterranean, and until all 34 other participants say "yes" to what Malta wants, Malta is saying "no" to everything everyone else has agreed to.

Maltese filibustering is part of security conference folklore. At the 1975 Helsinki meeting of the Conference of Security and Cooperation in Europe, Malta held out for, and got, a chapter in the final document dealing with security in its own region, the Mediterranean. The same occurred at the 1978 follow-up meeting in Belgrade when diplomats wearily pacified Malta with a minor meeting on Mediterranean security held in advance of the Madrid conference.

This time Malta, following the aggressively nonaligned dictates of its unpredictable premier, Dom Mintoff, has upped its stakes and is seeking a meeting on Mediterranean military security. This should be attended, according to Malta, by Mediterranean states including Syria, Libya and Israel.

The western allies, the East and the neutral nations pale at the thought of such a meeting, which is seen as bedeviling still further the already complex issues of East-West relations.

"What makes Malta think it has the right to a monopoly on discussion of Mediterranean security?" the chief Soviet delegate Anatoly Kovalev asked the plenary over the weekend.

"This is the longest Malta has stuck out," acting U.S. delegation chief Edward Killham said today. "People are looking for a way out, but there is no fallback position in the CSCE rule book."

The Helsinki procedure insists on consensus and delegates are wary of establishing a precedent by bypassing Malta to end the meeting here.

Concern is being voiced over plans to hold a formal closure of the Madrid proceedings attended by the foreign ministers of all the participating states the second week of September. This closure, which would permit a bilateral meeting between Secretary of State George P. Shultz and Soviet Foreign Minister Andrei Gromyko, could be jeopardized by the Maltese intransigence.

Bolstered by reported popularity back home in Valetta, where the Maltese government is depicted as courageously standing up to the superpowers, Saliba is adamant in his refusal to approve the document.

The exasperated diplomats arranged another plenary meeting for Thursday and said they would sit out the filibuster as long as necessary.