Gen. Juan Alberto Melgar Castro, 52, who served four years as Honduras chief of state. Melgar Castro had also been chief of the armed forces. He took power April 22, 1975, overthrowing Gen. Oswaldo Lopez Arellando, who had been chief of state since 1963. He in turn was ousted by the joint chiefs of staff on Aug. 9, 1979. They named Gen. Policarpo Paz Garcia to succeed him. Honduras returned to elected, civilian rule in 1982. Wednesday of a heart attack, in San Pedro Sula, Honduras.