It's celebrity weekend at the Watergate Hotel. Leonard Bernstein and Isaac Stern are in town to celebrate Roger Stevens' 75th birthday bash at the Kennedy Center tonight. Tomorrow night, ABC Monday Night Football sportscasters Joe Namath, Frank Gifford and O.J. Simpson will be staying there when they are in town to broadcast the Cardinals/Redskins game, and Beach Boys Mike Love, Carl Wilson, Bruce Johnston and Al Jardine have reserved 14 rooms while they perform at George Mason University's Patriot Center . . .

At a dinner sponsored by the National Diabetes Research Interchange Thursday night, Sen. Albert Gore received the Congressional Humanitarian Award and Edwin L. Artzt, president of Procter & Gamble, received the Corporate Humanitarian Award for their efforts against diabetes. Soap opera actress Gloria Loring, who has a diabetic child, sang "Amazing Grace." Also attending was Kathryn Iacocca, daughter of auto maker Lee Iacocca, who heads the Iacocca Foundation, which is dedicated to diabetes research . . .

Raisa Gorbachev, wife of Soviet leader Mikhail Gorbachev, seems to have an interest in fashion that goes beyond the utilitarian. Yesterday, while in Paris, she visited fashion designer Yves Saint Laurent, and the day before, she stopped in at Pierre Cardin's warehouse, where models showed her 60 costumes from the designer's winter collection . . .

Bert Parks, who was suddenly fired in 1980 after 25 years as host of the Miss America pageant, will oversee the crowning of another beauty contest winner. Today Parks will be master of ceremonies at the finals of the second annual Miss Asia Beauty Pageant at Madison Square Garden in New York. More than 100 contestants, age 18 to 27, from 15 countries are participating. "I love so many things about the Oriental peoples, like their reverence for the old," said the 70-year-old Parks.