Although she died nearly 25 years ago, the allure of Marilyn Monroe is still strong enough to have pulled in hundreds of M. M. fans to an elaborate tribute for the star at the Hollywood Roosevelt Hotel. Sponsored by Celebrity Focus magazine, the Tuesday event drew on the collections of fans, the portfolios of photographers and the wardrobes of costumers. "If Marilyn were here tonight, and according to what I believe she is here in spirit, I think she would say . . . 'I love all this,' " said actress Susan Strasberg, who was a personal friend of Monroe's.