Los Angeles Dodgers -- Assigned contract of 3B German Rivera to Houston Astros' Class AAA team in Tucson to complete trade from last week for IF-OF Enos Cabell. PRO FOOTBALL

Miami Dolphins -- Announced veteran FB Pete Johnson, who was told he would not be offered a contract unless he reduced his May weight of 286 pounds to 255, has not reported to early training camp. HOCKEY

Sweden -- Appointed Thomas Gradin, 29, coach of the national team, effective when his playing contract with the NHL Vancouver Canucks expires in 1987. COLLEGES

Idaho State -- Men's basketball program placed on probation for two years by NCAA Committee on Infractions, after an investigation found the team's former coach and a former assistant had committed several violations. Team was prohibited from postseason competition or live telecasts during the 1985-86 academic year. Probation effective June 19. SPECIAL OLYMPICS

People's Republic of China -- Has become the 68th nation to join Special Olympics International. Special Olympics is the world's largest program of sports training and athletic competition for mentally retarded children and adults. LOCALLY

Anheuser Busch/King Cobra Summer basketball league -- Seeks 25 participants for a slam-dunk contest. The winner will win a trip to the Bahamas. Registration, open to the public 18 years and older, is open until July 25. For details, Call the Maryland National Capital Park and Planning Commission.