Comedian Bob Hope has already signed on for the May 5 Mercury 7 Foundation benefit to raise money for scholarships and research study grants. It's too early to know where or what shape the gala will take, other than the date, which marks the 25th anniversary of astronaut Alan Shepard's historic ride into space . . .

The Erickson modeling and casting agency has been hard at work getting about 600 of its clients ready to be nonspeaking extras when the "Heartburn" movie crews move the shooting schedule to Washington from New York, where they have been filming. The movie company and casting agency are trying to be secretive about the location shots because they are afraid the presence of stars Jack Nicholson and Meryl Streep will draw a number of fans during the shooting here the first two weeks in October. Scenes will be shot at the Palm restaurant and in neighborhoods near the Adams-Morgan area . . .

It is billed as a "Salute to Jerry Herman," the Broadway composer of "La Cage aux Folles," "Mame" and "Hello Dolly," and more than 1,000 are expected to attend the $125-a-ticket fundraiser at the Shoreham Hotel Thursday. The money raised will benefit the Human Rights Fund and a gay rights or AIDS-related organization. Herman will be there to accept an award at the dinner emceed by sex expert-author-talk-show-host Dr. Ruth Westheimer. Rep. Henry Waxman, chairman of the House subcommittee authorizing funds for AIDS research, will be the evening's main speaker . . .

Looking to quell 23 years of rumors and allegations that Marilyn Monroe was murdered and her homicide covered up, Los Angeles police yesterday released a "lost report" saying the legendary film star apparently committed suicide. In releasing the once confidential report, police said they were attempting to dispel the years of "speculation and just plain lies" surrounding Monroe's death in 1962 from a drug overdose . . .

The 1858 Greek Revival house that was once the Georgetown home of Sen. Mark Hatfield is on the market with a $2.3 million asking price. The historic home at 3051 N St. NW has an indoor swimming pool, an exercise room and sauna and 11 fireplaces. The sellers boast that the four most recent U.S. presidents have dined there. It's nice to know that there's still an available house in Georgetown . . .