What if they gave a party and everybody came? That's pretty much what happened at the Beverly Hilton Hotel when the magnetic Gregory Peck received the American Film Institute's Life Achievement Award. Two thousand of Peck's closest friends packed into the hotel's ballroom and greeted the 72-year-old actor with a thunderous standing ovation. The big-screen definition of debonair nearly lost his cool threading his way through the thicket of hugs, kisses and congratulatory pats that came from such diverse stars as Jimmy Stewart, Justine Bateman, Olivia de Havilland, Sidney Poitier, Chevy Chase, Jimmy Smits and Jane Fonda. (The last two will appear with Peck this fall in Old Gringo, his newest film.) Audrey Hepburn hosted the do and introduced clips from Peck's 46-year career, including scenes from Duel in the Sun, Roman Holiday, Moby Dick, Gentleman's Agreement and his Oscar-winning To Kill a Mockingbird. After two standing ovations (a third was yet to come), Peck took the podium, thanked his family and claimed he was "still trying to figure out how I got here." Which is, of course, precisely the attitude that put him there.