GENEVA, NOV. 12 -- Crucial talks on reforming world farm trade are deadlocked, jeopardizing a planned meeting of ministers in Brussels next month to wind up four years of broader trade negotiations, the top official of the GATT trade organization said today.

"It is obvious that we are now in a very grave situation," said Arthur Dunkel, director-general of the General Agreement on Tariffs and Trade, the Geneva-based group under whose auspices the talks are being held.

"Until and unless some major political decisions are taken, the negotiations will not move forward," Dunkel told the steering committee of the 105 nations that have been trying to negotiate a series of trade reforms.

"These decisions are therefore urgent and essential and it is not an exaggeration to say that the Brussels meeting is now in jeopardy," he said.

But GATT spokesman David Woods later told reporters the conference would still take place, although it is unlikely that a complete trade package can be agreed upon in the scheduled four or five days of talks.

Farm subsidies, especially export subsidies, have been the main sticking point in the international trade talks, which cover everything from basic farm produce to such esoteric invisibles as reinsurance.

Ministers are due to meet in the Belgian capital from Dec. 3 to Dec. 7 to put final touches on the trade reform package.

Dunkel convened the steering committee after the United States and others rejected as inadequate a proposal from the 12-nation European Community to reduce agricultural subsidies and support by 30 percent from 1986 levels.

The United States and other food-exporting nations have proposed that internal supports be cut by 75 percent and export subsidies by 90 percent.

"At our last meeting, on Nov. 2, I referred to the deadlock in agriculture. I am sorry to have to tell you that the situation today is no better," Dunkel said.

Under pressure from its 10 million farmers not to reduce government support, the EC struggled hard just to come up with its 30 percent offer -- but it was plainly seen as insufficient.

"In the view of a number of participants, that offer, and possibly others, does not constitute an adequate basis on which to conduct substantive negotiations," Dunkel said.

He said critics questioned whether the EC proposal was consistent with commitments taken in 1986 at the beginning of the trade negotiations or at a mid-term meeting last year, when it was agreed to make progressive and substantial cuts in farm support.

Talks on agriculture broke off over the weekend after the United States and delegates from the 14-member Cairns Group of farm-exporting nations indicated they were not prepared to negotiate unless the EC and some others improve their offers.

Separately, the dispute over farm trade spilled over today into broader U.S.-Europe foreign policy.

European Community foreign ministers delayed signing a declaration with the United States on shared principles such as democracy and market economics because of a U.S. demand that a commitment to concluding the trade talks successfully be included in the declaration.

"We believe that this reference has no place in a declaration which focuses essentially on the future," French Foreign Minister Roland Dumas said of the document that will guide EC relations with Washington into the next century.