Clarence Streit, a man who has dedicated a long, event-filled life to world peace and to a federal union of the democracies of the world, turned 90 yesterday. Over the years supporters of Streit, who is still president of the Association to Unite the Democracies, have included Barry Goldwater, Richard Nixon, Gerald Ford, Mark Hatfield, Harry Truman and Hubert Humphrey.

During his long career as a foreign correspondent, Streit covered the Greco-Turkish War, Mussolini's rise to power and the birth of the Turkish and Greek republics, all before 1925. He also covered the brief life of the League of Nations for The New York Times and his later book, "Union Now," became a best seller. A sizable group of friends and associates threw a birthday luncheon, appropriately enough at the International Club, yesterday for Streit, who is still fighting for the union of democracies. Among the guests there were former senators Eugene McCarthy and Gale McGee, former representative Walter H. Judd and retired ambassadors Arthur Burns and Theodore Achilles. Protesting Apartheid

Monday's national observance of the birthday of Martin Luther King Jr. affected people in different ways, from those who had actually known him and followed him to those who see him only as a major historical figure. Washington businessman Jeff Gildenhorn, who owns restaurants and two seafood markets on Connecticut Avenue, watched television Monday and was troubled by the parallels between the pre-1960s race problems in the United States and the present violent segregationist policies of the South African government.

He said he decided to make his own statement in memory of King by banning South African lobster tails from all his stores. He said he intends to carry his boycott to the National Restaurant Association, hoping that others in the restaurant and seafood business across the nation will stop carrying South African food products like the rock lobster, a popular selling item. End Notes

Fresh from the Martin Luther King birthday celebration party at the Pension Building Monday night, superstar Stevie Wonder spent some time in the Fairfax Bar at the Ritz-Carlton Hotel listening to pianist Peter Robinson. Wonder then surprised the patrons in the crowded bar by taking over the piano and leading a sing-along, including his "Happy Birthday" to King song. In the audience was singer Bob Dylan. The Ritz-Carlton had a significant share of the show business celebrities in town, including Wonder, Dylan, Diana Ross, Gregory Hines, Eddie Murphy, Quincy Jones, Peter, Paul and Mary, the Pointer Sisters, Elizabeth Taylor and Judith Jamison. The front of that hotel was an autograph hunter's paradise . . .

Cleveland really wants the Rock 'n' Roll Hall of Fame. Cleveland is not usually the city one thinks of when one is contemplating famous rock 'n' rollers, but a couple of disc jockeys there have so stirred up the public that of 131,208 calls made for a poll by USA Today, 110,315 voted for Cleveland. Whatever happened to Nashville and Philadelphia . . .

Thomas R. Kendrick, the former Kennedy Center director of operations, is recovering from a mild heart attack in Hogue Memorial Hospital in Newport Beach, Calif. The 52-year-old executive director of the Orange County Performing Arts Center has been in the hospital since Jan. 12. He underwent a balloon dilation of his coronary arteries last week to improve his blood flow. He is expected to be released from the hospital in a couple of days and to return to work in several weeks. Kendrick is also a former Washington Post assistant managing editor . . .

Richard Blackwell has released his 26th annual 10 Worst-Dressed Women list. And the top honor goes to Princess Stephanie of Monaco for her "unisex wardrobe that entitles her to use either bathroom." Stephanie seems to have worked hard at making the list. Others who have worked hard and apparently spent their hard-earned money to dress the way they do are Joan Collins, Madonna, Tina Turner, Michele Lee, Whoopi Goldberg, Cybill Shepherd, Lisa Hartman, Apollonia and Heather Thomas. He also named model-actress Lauren Hutton as the "Fabulous Woman of the Year" and gave entertainer Liberace the "Halley's Comet" award for his "out-of-this-world, brilliant array of flashy, glitzy glamour" . . .