WASHINGTON (AP) _ The Supreme Court Monday refused to force the federal government to compensate U.S. citizens whose land in El Salvador was seized by that government.

The court, without comment, rejected an appeal by six landowners who said El Salvador took their coffee plantation in 1980 in a land reform program urged by the U.S. government.

A federal appeals court here denied the compensation claim last March. It ruled that the U.S. government's involvement in El Salvador's land reform was not ''sufficiently direct and substantial'' to require the United States to pay the landowners.

The Constitution generally requires the government to pay ''just compensation'' when it seizes private property.

The appeals court said the landowners may be able to gain compensation for their loss through international arbitration.

The claim was made by the owners of Las Lahas, a 4,500-acre plantation said to be worth more than $20 million.

The former owners are Fred E. Langenegger of Whitewater, Kan.; Steven W. Langenegger of Burns, Kan.; James Langenegger of Hagerman, N.M., Ida Anna Nolder of Manhattan, Kan.; Floreine Edith Stangle of Wichita, Kan., and Emma Frieda Zuercher of Benton, Kan.

They inherited the land from their cousin, Blanca Rosa Langenegger of El Salvador, when she died in 1978.

They said the United States was responsible for the land reform program because the federal government threatened to cut off economic and military aid if El Salvador refused to go along. They also said U.S. officials helped draft the Central-American country's agrarian reform plans.

The plantation was seized by El Salvador's military government, installed in a 1979 coup.

Last May, in a similar case, the Supreme Court overturned a ruling that could have allowed a U.S. citizen to recover damages for his land in Honduras - taken over for a U.S. military training center there.

The justices in that case ordered further lower court review in light of federal legislation that could help the landowner.