A sudden dispute between the United States and the European Community over agricultural policy today threatened to halt negotiations on a new round of international trade talks.

The dispute, which came to a head in an all-night meeting that ended this morning, centered on a demand by the United States that the new global round discuss agricultural export subsidies when it considers agriculture as a whole in 1987.

The EC had agreed to include the matter, but EC Ambassador Tran Van Tinh put the topic off bounds.

The dispute flared during a week of behind-the-scenes negotiations in the preparatory committee, which is drafting an agenda for the new trade round. This agenda will be completed at a meeting of trade ministers of the 92 members of the General Agreement on Tariffs and Trade (GATT), the international organization that regulates world trade. The meeting is scheduled in Uruguay Sept. 15, and the new round itself will kick off early in 1987.

The question of including services, such as banking and insurance, in the new round had been the major stumbling block in drafting an agenda. A group of developing countries led by India and Brazil consistently has blocked this idea, which is being pushed by the United States, on the grounds that GATT is about trade in goods, not services.