The Air Force announced yesterday it would appeal a federal court ruling here earlier this week that ordered the reinstatement of former Sgt. Leonard P. Matlovich, a decorated Vietnam vetern who was discharged from the service in 1975 after professing his homosexuality.

U.S. District Court Judge Gehard A. Gesell said Tuesday that the Air Force failed to show a clear reasonable standard for discharging Matlovich, who sought the court order case as a test of the service's policy toward homosexuals.

Matlovich, 37, was a 12-year veteran of the service when he wrote a letter in 1975 declaring his homosexuality to then-secretary of the Air Force John McLucas. The Air Force quickly discharged him.

Matlovich, a technical sergeant who had been stationed at Langley Air Force Base, Va., sued in Gesell's court but lost. His appeal to a higher court in 1978 resulted in the return of the case to Gesell's court for clarification on the Air Force's standards on discharging homosexuals. Gesell ruled that the service's standards were too confusing and ordered Matlovich, whose attorneys said could receive about $50,000 in back pay, has declared he would return to the Air Force as an example to other homosexuals serving in the military.