The failure of the world's trade ministers to reach a meaningful accord last week at a highly emotional marathon session in Geneva is bound to accelerate protectionist pressures around the world, experts inside and out of the Reagan administration agreed yesterday.

Even for the record, U.S. Trade Representative William Brock would claim only a "partial success" for the meeting, and that only because the "trading system is still intact." Brock would grade the conference as less than a 'C'. "It could stretch to a 'C', but only time and future action will tell," he said at the session's conclusion.

In less diplomatic language, the highly touted meeting of the ministers of the 88-nation General Agreement on Tariffs and Trade (GATT) -- the first in nine years -- failed to produce agreement on a modest budget of items designed to improve trade relations or on an "agenda" of future liberalizing negotiations for the rest of this decade.

The GATT session approved only a watered-down communique that promised "to resist" new protectionist measures. But the signatories didn't say how they would do so. The Australian government, terming the agreement meaningless, refused to sign it.

Further weakening the meaning of the final agreement, Wilhelm Haverkampf, vice president of the Common Market Commission, said that it was not a "commitment" on the Europeans' part, only an undertaking to use "best efforts" to avoid protectionist measures.

The communique also promised to begin a two-year study of the impact on trade of agricultural subsidies of the kind the European countries give their farmers. But there is no explicit mention of export subsidies, which the United States wants to combat. Even so, the community was quick to assert that the communique did not commit it "to any new negotiations or obligations in relation to agricultural products."

Agriculture Secretary John R. Block lost no time in threatening action to ensure American farmers greater access to the world market. He would not elaborate yesterday on exactly what steps the Reagan administration might take, or when it might take them.

Privately, trade experts in and out of the U.S. government could not contain their gloom over what must reasonably be considered an unanticipated disaster that threatens the existing system of open international trade. No one had looked for great successes, but no one had anticipated what amounted to stalemate.

Some Reagan administration officials and congressional trade spokesmen said they will now be pushed into strategic interventions to protect American interests in agriculture, high-technology, and other areas.

"When I was in Geneva, I warned the member nations that failure to reach accord on a number of pressing trade issues could set the stage for a wave of protectionist legislation. Unfortunately, this kind of legislation is now more likely than ever," said Sen. Robert Dole (R-Kan.), a member of the U.S. delegation, on his return to Washington yesterday.

Dole said GATT "is in serious difficulty," and that his Finance Committee would begin hearings on Jan. 25, 1983, "to review the results of the Geneva conference and to reassess U.S. involvement in the GATT system."

In a real sense, the villain of the piece is the worldwide economic recession, which is so deep that most nations present at Geneva, under pressure not to let unemployment grow, were fearful of taking any step that might cost jobs in the short run. The United States took the leadership in an effort to preserve and extend a multilateral system, but except for support from Australia and New Zealand (who also are angered by the European stand on agriculture), the American effort fell short.

"The GATT itself may be dead as a multilateral trade forum," said one official who would not let his name be used. There is talk among some administration officials of trying to evolve a smaller group of like-minded nations, that would exclude the European Community, to try to maintain some semblance of free trade.

Some U.S. officials could not hide their anger at the European Community, which they say allowed an anti-American French delegation, led by Foreign Trade Minister Michel Jobert, to set the tone.

"It was the Europeans who torpedoed this conference," said an aide to a member of the American delegation, which included representatives from several government departments and members of Congress.