Agricultural leaders from the United States, the European Community and other countries face each other here Thursday in the first public debate oncutting farming supports since the EC adopted limits on grain and oilseeds spending in February.

U.S. Agriculture Secretary Richard Lyng, EC Agriculture Commissioner Frans Andriessen and Australian Primary Industries Minister John Kerin are opening speakers at the two-day World Food Conference, organized by European Parliament President Henry Plumb to discuss the problem of persistent food shortages in the Third World despite food surpluses in the West.Mr. Lyng may use the conference as an opportunity to demonstrate why the United States is not impressed by the so-called stabilizers on Common Agricultural Policy costs, diplomats here said.

Mr. Andriessen, who met U.S. officials in Washington after the stabilizers were agreed, believes the United States should give credit to the community for its agricultural cutbacks over recent years, which culminated in February's grain and oilseeds restrictions.

However, the United States says the grain stabilizer set EC output at 120 percent of consumption with only minimum price penalties, and in any case

keeps EC cereals support at twice the world price.

The United States maintains that the supposed limit on total EC farm spending still allows an increase of 20 percent this year and has several loopholes permitting even greater expenditure on currency or foreign trade grounds.

The diplomats said that with Mr. Kerin likely to put forward the views of the Cairns Group of agricultural free-trading nations, the Thursday conference could reflect the principal farm issues under discussion in the Uruguay Round. Only Japan is not represented among the major General Agreement on Tariffs and Trade participants.

However, European Commission sources noted that the conference will not become the scene of a U.S.-EC confrontation on farm trade as it is dealing with much wider subjects.