The D.C. Court of Appeals yesterday overturned a 1985 decision by the Board of Zoning Adjustment that rejected plans by the People's Republic of Benin to build a controversial 38-foot radio antenna in the back yard of its Northwest Washington embassy.

The court's decision struck down a 4-to-0 ruling by the zoning board that was hailed at the time by the Woodley Park Community Association, whose members said the tower at the Cathedral Avenue embassy would detract from the affluent neighborhood just west of the National Zoo.

In its decision yesterday, the appeals court said the D.C. zoning board applied an improper standard in considering the application to build the radio tower. The court said the local board had treated the application as it would a request by any property owner.

Rather, the court said, such requests by foreign governments are subject to a 1982 federal law that imposes restrictions on the District's ability to reject such requests.

Benin, a West African nation whose embassy was established in 1967, has been trying to win approval for the tower since November 1979. Embassy officials have sought the antenna for a direct radio link with their capital city of Contonou. Without the radio, they said they must rely on diplomatic mail, telephone or telex communications.

Embassy officials were unavailable for comment yesterday, as were District officials.

Marc Palay, the attorney for Benin in the case, said the decision was "a good and important ruling" for the country, but he said he was still studying the decision and had not decided on recommendations about what the embassy should do next.

Among the options, he said, would be to start the process anew or to simply proceed with construction of the tower.

The federal law requires an embassy to obtain local permission to construct an addition to the embassy, but places limits on a local jurisdiction's ability to deny the request.

Palay said the embassy could be required to submit an application to the Special Board of Zoning Adjustment, which includes representatives of the federal government as well as the local board. The 1985 ruling was made by the D.C. board, which comprises only District officials.

The special board would be required to consider the application in the context of specific standards in the 1982 Foreign Missions Act.

The first of those considerations is "the international obligation of the United States to facilitate the provision of adequate and secure facilities for foreign missions in the nation's capital." The zoning board in 1985 did not take that factor into consideration.

This year, without obtaining permission from the D.C. government, the Ethiopian Embassy at 2134 Kalorama Rd. NW erected a radio antenna like the one planned by Benin. Although residents protested, city officials discovered they were essentially powerless to enforce the zoning laws through the courts against an embassy determined to ignore them.