TO BE ACTIVE IN EUROPEU.S. farm groups should take a more aggressive role in developing new markets in Eastern Europe, Agriculture Secretary Clayton Yeutter said Thursday.

''It may be premature to put an office over there or invest in privatizing farms, but we should be stirring in the arena so we can become players in the market," said Mr. Yeutter, speaking at a Commodity Club luncheon here.

Mr. Yeutter said commodity groups in the United States have taken a wait- and-see-approach about becoming involved in Eastern Europe, although most consider the newly emerged democracies in the region as "a good opportunity."

He said it is important the United States develop firm business contacts in the region before it becomes monopolized by European Community interests.

''Not long ago there was a food fair in Poland with 500 exhibitors, but only one was from Illinois in the U.S.," Mr. Yeutter said. "If 499 of the exhibitors are not from the U.S., we won't make a lot of business."