Marshall Brickman has a heart of glass. It sits on his desk 15 floors above Manhattan's Central Park. Mary Tyler Moore lives in the same building. So does Diane Keaton. Brickman, Woody Allen's collaborator on "Sleeper," "Annie Hall" and "Manhattan," lives above lyricist Fred ("Cabaret") Ebb. When Brickman's 3-year-old daughter, Jessica, toddles too loudly across the bare wood floors, he hisses "fredeb . . . fredeb."

"She thinks that means be quiet now."

Tall, witty and terminally urbane, Brickman toys with the small heart and talks about his latest film, "Lovesick," a comedy about a middle-aged Manhattan psychoanalyst (Dudley Moore) who falls in love with his 21-year-old patient (Elizabeth McGovern). "Lovesick," which is his second solo venture, could once and for all dispel the notion that Allen and Brickman--the Simon and Garfunkel of filmmaking--are not as talented individually as they are together.

"We're different people," Brickman says. "We came together when our common point of view was very useful to the projects we worked on."

They met in 1963 at the Bitter End. Brickman played banjo for a group called the Tarriers. Allen was a stand-up comic. Brickman began writing jokes for Allen, and at the age of 27 became the youngest head writer for Johnny Carson's "Tonight Show."

But the brooding boy genius from Brooklyn found his true comedic calling as Allen's collaborator. In fact, the three films they made together remain the most successful of Allen's ventures. "Marshall makes my game better," Woody Allen once told a reporter. "It's like playing tennis with a pro."

Since the partnership ended, Allen has made two commercial failures, "Stardust Memories" and "A Midsummer Night's Sex Comedy." Brickman broke out on his own in 1980, with the Alan Arkin vehicle "Simon," also a box-office failure.

He remains cautiously optimistic about "Lovesick." "I'm always amazed that something I've invented might make people laugh in Lubbock, Texas, a place I've never even been to."

If it does succeed, Brickman's name might even be mentioned without the perennial tag line, "Woody Allen's collaborator."

He begrudges the fact that people still see him as a Woody Allen clone. The two remain friends, Brickman says, though perhaps not as close as they once were. Still, Woody Allen is on the wall, staring out from a photograph. The initials "W.A." are at the top of the penciled-in list on Brickman's direct-line telephone. The Oscar they won in 1977 for "Annie Hall" (best screenplay) sits in one corner partly hidden under a stuffed animal.

Is Marshall Brickman Woody Allen's alter ego? "That's the handle I was known by," he shrugs. They talk alike, the same Brooklyn accent, the same inflections, the same kibitzing. They dress alike, in L.L. Bean urban intellectual uniforms of khakis, plaid shirts and sensible shoes. They even look a little alike, though Brickman is a head taller. With his high forehead, wire glasses and close-cropped hair, he looks more like Neil Simon than he does Alvy Singer.

The phone is ringing. "I promise this is the last call I'll take," he says. He is preoccupied by the early box office figures. He sits in his slightly cluttered study, furnished with antique country furniture. The walls are covered with photographs, framed awards and a gold record. Brickman used to play the banjo, and recorded an album with Eric Weissberg that included a song called "Dueling Banjos." In 1972, the album was turned into the soundtrack for "Deliverance," winning two gold records and providing Brickman with the financial freedom to give up writing comedy for Johnny Carson, quit his job as producer of the Dick Cavett show and join Allen writing screenplays full time.

His wife, film editor Nina Feinberg, walks into the room. He introduces her as "Johanna." She walks out.

"Did I just call her Johanna?" Brickman muses, as the door closes. "Freudian slip."

He doesn't laugh easily. He is not given to sudden bursts of spontaneity. He is a shy, serious humorist, and is somewhat guarded about his personal life. He says he is merely "pensive." At least, he says, he's not as depressed as he once was.

He says "Lovesick" is not an art film. "Woody has a very particular approach. Woody has never had a whole lot of confidence in his stuff commercially. It's him. His films were always conceived to be much more parochial than this film. And that's a much safer way to go."

Brickman says he doesn't know if Allen has seen the film. He never read the screenplay. "We don't show each other things," he says. Too much respect for each other's opinion? "Exactly. You must follow your own intuition."

Brickman's intuition may be right on the money. "Lovesick," which cost less than $10 million to make, grossed nearly $6 million in its first 10 days. Most reviews have been good, although Brickman says if it finds an audience, it will be the result of word-of-mouth rather than critical acclaim.

He examines the heart.

"I wanted to do an idealized romantic relationship. I wanted to do a story where somebody gets rewarded for doing the right thing," he says. "There's nothing wrong in not punishing the hero."

Some see Marshall Brickman as the humane side of the "Annie Hall-Manhattan" brand of brainy urban comedy, heavy on free-floating Jewish angst. Others call him an elitist, a man who keeps his own ambition under wraps while appearing to disdain the trappings of success.

"There's a part of me that's very much like my first film," he says, referring to "Simon." "Cold. Calculating. It's about technology. Machinery. And it's full of ideas. Very intellectual. Very cerebral. And you don't care at all about the characters."

"Lovesick" is a happier film. Maybe it's because Brickman himself is happier. At the age of 43, he is cascading into middle age with a wife, a child, a cat, a few goldfish, a Cuisinart on the counter and a woman who cleans his Central Park West condo. All that may have cushioned his caustic outlook on life. Especially the child.

"I think I accept some emotions in myself now that I didn't know about," he says quietly.

Does Brickman have more heart than Allen?

"You'll have to ask his cardiologist."

He forces a smile. He is not comfortable with the press.

"Does this make any sense at all?" he says winding up a five-minute monologue in which he reveals: 1. His analysis lasted seven years. ("It was a good substitute for being an Episcopalian. It gave you a point of view.") 2. He stopped yearning for success last Saturday night. 3. He is worried about the tape recorder. It's too far away.

"I mean, what if you get home and there's nothing on it?"

He opens his top drawer and pulls out a blank tape. Just in case the tape runs out or breaks in the middle of a brilliant quote or self-destructs in a puff of smoke. Marshall Brickman, like Woody Allen, worries a lot.

"Whenever something goes right, it's a miracle," he once told a reporter. "And you should wonder what God is saving up for you later."

Central Park is teeming with trendy Manhattanites on this mild, spring-like afternoon. Marshall Brickman says if it weren't for the park, New Yorkers would go to war against each other.

"I mean, look around," he says. "Here, they can let off steam."

A woman wearing a mink sweatshirt is walking two perfectly groomed Pomeranians. A man in Nikes is jogging backward.

"There's a guy who's really worried about being followed."

Brickman is soaking it all up.

Two well-dressed women stroll by. One says to the other, "You know, that's the first time a stranger has ever said to me, 'Have a nice day.' "

Brickman rolls his eyes. "You know what really bothers me?" he says, loping along the narrow path. "Every time I call information and ask for a number, the operator gives the number then says, 'Have a nice day.' "

He pauses for effect. "And then I forget the number." He shakes his head. "346-6745. Have a nice day."

This is how he worked with Woody Allen. The two would walk for hours, and the whining and kvetching about people who say, "Jeet? No, Jew?" would later turn up as dialogue.

At the Plaza Hotel, there's an uncomfortable moment with an uncooperative maitre d'. Brickman leaves, headed for his favorite haunt, the Russian Tea Room ("They know me there") where he will order ginger beer, pea soup and a caviar-egg concoction. For three city blocks, he analyzes the scene with the maitre d'. "He sensed my hostility," Brickman says, sounding more and more like a character from one of his own films. "Do you think he sensed my hostility?"

Back in Brickman's study, he says he didn't mean to avoid the question of whether or not he is happy.

"I think a better way to phrase the question would have been, 'How do you feel about the film?' "

How does he feel about the film?

"Fine."

He leans back in his chair, hands behind his head.

"I thought it would be a funny, comical situation, and it is. In fact, I couldn't believe that no one had done it before. It's such a natural, really, for an urban romantic comedy."

Some might see it as a slam against psychoanalysis.

"It's a tender subject," he says. "I never thought there would be this kind of reaction. They showed the movie to 350 psychoanalysts in Los Angeles and there was a lot of laughter during the show and then when the lights came up during the discussion, there was a lot of outrage. The analysts were saying, 'We don't think this is going to do anybody any good.' It's too bad. Anything that can be attacked by this nice little film is in a shaky position anyway.

"Doctors are the last priesthood," he says. "They're the last unassailable group. Politics is not a good subject for any kind of humorous satire after Nixon because Watergate was so broad and more bizarre and more surreal than anything you could invent. You have to tell the audience something that it doesn't already know. Or you have to find a subject that the audience is having skepticism about, a little suspicion about. If people suspect that politicians are corrupt but aren't convinced, then you can do a good piece about it. But if people are convinced, then they'll say, 'What else is new?' People still trust doctors and is this boring you? I knew it."

Brickman once said "Simon" was a film for the '70s. Is "Lovesick" a film for the '80s? Are we in for a decade of warmth?

"Yes," he says forcing a laugh. "It's the step right before Fascism."

Marshall Brickman says his goal in life is "not to be an a--. Not to be pompous."

He looks dead serious. "I am an a--. But I'm very skillful."