Here's what lunch with Diane Keaton is like: She marches into the restaurant, a long, lean coatrack of a woman trailing fabric. It's 95 degrees in Los Angeles, and she's covered up in jeans, a black skirt, a scarf, and a black blazer knotted around her waist. She sits down laughing, her great tootle filling up an otherwise hushed room. She throws her limbs around when she tells stories, and will lean over and grab your arm when she gets really excited. She dances from subject to subject, from her new movie with Jack Nicholson (''Something's Gotta Give,'' due Dec. 12) to the old ones with Woody Allen. Because her train of thought is so prone to derailing, big yarns can unravel in grand ''Annie Hall'' fashion: ''Oh, that was so much fun. Ahhhhh. I know. Yeah. No. Well, I dunno what to say. You know, I'm sort of like, kind of like, oh I dunno, I dunno, ya know?''
It's a ball, really, and when she says goodbye some two hours later -- ''I'm going to skiddoodle!'' -- you're left grinning dumbly, staring after this bundle of intellect and nerves.
Woody Allen sure fell for her easy mirth, casting his muse in films like ''Sleeper,'' ''Manhattan,'' and, of course, ''Annie Hall,'' for which she won an Academy Award in 1978. ''She was great when I met her 30 years ago,'' Allen says today. ''She's been great for decades and manages to continue to be great.'' ''Something's Gotta Give'' director Nancy Meyers is another of Keaton's admirers, having also worked with the actress in 1987's ''Baby Boom'' and both ''Father of the Bride'' pictures. ''Diane is in the great tradition of the screen heroines I've always loved,'' says Meyers. ''Irene Dunne, Carole Lombard, Katharine Hepburn.''
Why, then, is it so hard for Keaton to find good work?
''It's not exactly easy to get me on a major movie,'' she says. ''What is the box office appeal of me? It's absolutely nonexistent. Nonexistent!'' Sony execs had to be convinced that the 57-year-old actress was the right choice for ''Something's Gotta Give.'' ''It's true that she perhaps wasn't the first person they thought of,'' admits Meyers, who wrote the role of a middle-aged woman courted by two generations of men with Keaton in mind. ''They just had to be reminded how great she was. It's cliche, but they tend to think, What did they do last? For a woman in her 50s, the material isn't there. So they didn't have an immediate frame of reference for Diane. 'Oh, yeah, she was the lead in...' No! She wasn't the lead in anything for a while.''
Well, merry Christmas, she's back. In her new romantic comedy, Jack Nicholson chases hard after her. So does Keanu Reeves. Finally, it's the older woman showing a young buck how good it can get.
In Recent years, Keaton has played a sensible mother (''Father of the Bride'' I and II), a stunned divorcee (''The First Wives Club''), and an unmarried cancer victim (''Marvin's Room,'' for which she was nominated for an Academy Award).
Oh, but she used to play the lover. In Warren Beatty's ''Reds,'' she was fiery and alive (and earned another Oscar nod). She was the apple-cheeked naif to Al Pacino's brooding mobster in the ''Godfather'' films. And whether expounding on the banality of Van Gogh (Van Gaaach) in ''Manhattan'' or twirling about a tennis racket in ''Annie Hall,'' Keaton was the cute get in Woody Allen's best movies.