"Is America really going to self-destruct, Dr. Karl?" an earnest young social worker asked the dean of American psychiatry on the eve of his 90th birthday.

Karl Menninger leaned forward on his gnarled cane and took a long, steady look around the small conference room where two dozen child-care professionals had gathered to wish their mentor happy birthday. The conversation had originally been about fighting among children, but Menninger had skillfully maneuvered it to the current dragon he is trying to slay--what he calls the suicidal spiral of fighting among nations, an issue he says is "the single greatest mental health problem in the world today."

"Of course we're going to self-destruct," Menninger replied with unquestionable certainty, as if he'd been asked whether 1 plus 1 equals 2. "At the present rate we're going, that's the plan."

He fixed the young woman with a flat stare--the expression he saves for those who ask silly questions, chew gum, interrupt him or speak into his deaf right ear.

"Piling up rocks is no way to settle a dispute. One side gets rocks so the other side gets bricks. Then they boast, 'My pile is bigger than your pile.' That's the way children talk."

His voice dropped from growling to gentleness. "If a patient did that, do you know what a psychiatrist would say? 'Why destroy yourself?' In the last analysis, a good deal of a psychiatrist's talk with a patient is simply this: 'Don't take revenge. That's going to hurt you worse than it'll hurt them."

At 90, the man who introduced psychiatry to the American public is--as friends say he has always been--a brilliant, difficult but lovable curmudgeon.

"Karl is a man who inspires mixed feelings in everybody," says Harvard psychologist Philip Holzman, a former pupil and coauthor of one of Menninger's 13 books. "There isn't anybody who completely likes him or who completely hates him. But they all love him."

This past weekend, Topeka showered its affection on the man who helped put it on the map as the "Vienna of the Wheatfields" by hosting a nonstop volley of receptions, presentations and birthday parties. Despite the current merciless heat wave, serious brain surgery seven years ago and a stroke early last year, Menninger gave speeches, greeted friends from around the country and graciously listened to countless off-key renditions of "Happy Birthday."

Boundless energy--coupled with a fierce sense of duty and a no-holds-barred curiosity--has distinguished the formidable psychiatrist, author, teacher and crusader throughout a remarkable career that began in 1925 when he founded, with his father and brother, the world's first psychoanalytic hospital. Today that converted Kansas farmhouse has blossomed into the prestigious 310-acre Menninger Foundation, which employs more than 1,000 people and boasts an annual budget of $42 million in a combination of public and private funds.

Dr. Karl--as he is called partly through affection and partly to separate him from the rest of the Menninger family psychiatric dynasty, which includes his son Dr. Bob and his nephews Dr. Roy and Dr. Walt--still puts in a 5 1/2-day week in his office at the foundation, where he is chairman of the board of trustees. His daily routine includes reading several newspapers and magazines, preparing for lectures and teaching commitments and corresponding with professors, politicians and psychologists around the world. But his major project is writing his 14th book, tentatively titled "The Suicidal Intention of Nuclear Armament." Its theme is a subject Menninger repeatedly introduced throughout his birthday weekend--"The great and growing suicide club Americans seem to be caught in."

In his memorabilia-lined office, just before the whirlwind weekend of birthday-partying, Menninger is willing to talk about anything or anyone but himself and his work. Instead, he prefers to show off some of the artifacts in the museum-like room. "This is my new hobby, collecting polished spheres," he says, pointing to two stone globes at the center of his desk. Nearby is a small birthday cake and a handwritten card from some children he has worked with. "Have a piece," he insists. "It's made of some kind of squash but it's pretty darn good anyway."

Menninger settles into a deep leather armchair behind the cluttered desk and begins rocking back and forth. The wall beside him is decorated with family photos, the far wall with a gallery of inspiring individuals--Albert Schweitzer, Eleanor Roosevelt, Sigmund Freud. "Look at that one of Helen Keller feeling my face," he says. "She told me she wanted to feel my face so she'd recognize me the next time she saw me. Those are the most famous words that have ever been spoken to me."

One corner of Menninger's desk is covered with the day's stack of magazine articles, clipped and marked for distribution to specified individuals. ("No one leaves his office without a book or article," says a friend. "He feels compelled to give things and considers a new idea the best gift of all.") Menninger starts to talk about The Villages, an organization he founded for homeless, neglected and abused children, then suddenly blurts out what's really on his mind.

"I get nervous at these things," he admits early in the interview, standing up to get his jacket because "I can't talk to a lady without one." Running a large hand through his white hair, he asserts, "I don't want publicity. What's so special about me? That I've lived 90 years?"

He sits down for about 30 seconds, then is up again with a "Let me show you something," and a surprisingly vise-like grip on his visitor's elbow. He walks into an adjacent library whose shelves are marked with neat hand-lettered signs--including one for "Evil People" that includes biographies of Adolf Hitler, Richard Nixon and Lyndon Johnson. "I used to admire LBJ," he says sadly, "but then he got ambitious and unscrupulous."

Menninger pulls a book about the Hopi Indians off another shelf and notes that he's giving away his collection of American Indian dolls to a museum. "I'm 89 and 364 days old," he announces, "and I've discovered that the only way to keep things is to give them away."

Now, he says, "Let's talk." But before returning to his desk, he stops at a poster of the universe taped to the library wall. "This is one of my meditation spots," he says, gazing at the sea of galaxies. "What is 90 years compared to 90 billion?"

"Psychiatry is a much more helpful profession today than when I started," Menninger says, comfortable now in his desk chair. "Back then we were supposed to lock up lunatics. Nobody realized they could be helped."

One current psychological direction he considers harmful, however, is "selfism . . . the pseudo-religion of ego-inflation and self-worship. Why should we need to overcome our inhibitions? Some of us had better develop some."

Another dangerous trend, he says, is that "the lawyers won't let us alone. Psychiatrists ought not to be allowed in a courtroom any more than lawyers are allowed in an operating room. I've dealt with what you call crazy people all my life and I don't know what they mean by insanity. I've heard it defined this way--it's something like the Yiddish word 'tref' unclean . But we all have a little of that in us."

Mental-health professionals should be allowed to examine an offender, he says, only after a case has been tried, and then they can report their views to the court. "Matters of guilt, competence or responsibility are moral questions, not medical ones," he says. The judges and jury are "the representatives of the community . . . who should express the community's sentiments on moral questions; we psychiatrists are not."

While "early psychiatry was about disease," he notes, "psychiatry today is about life problems . . . like 'Why did I do that?' or 'Should I leave my husband because he beats me?' " Most of these problems, he says, center "on the lack of an ability to sustain hope or faith or love." The remedy: "encouraging each other in this hope business."

But the major life problem "people are generally unaware of," he says, "is how dangerous this bomb business is. I think Reagan pretty well speaks a certain kind of 'Main Street,' 'Babbitt' mind that thinks, 'Nobody's going to do that to me.' "

This attitude typifies, he says, "a kind of primitive pay-back virus in people that gets us in a lot of trouble. In my opinion, revenge is the most dangerous disease in the world."

It is not surprising that the author of "Man Against Himself"--a now-classic examination of humanity's inherent death wish--considers nuclear armament not just homicidal, but suicidal. Over the past few years he has mounted a campaign that echoes the theme of another of his books--"Love Against Hate."

"We've got to talk about this nuclear thing," he says. "We mustn't say, 'It's hopeless,' and let the big shots call the shots. I think we ought to be more optimistic about life. Look at the Athletes for Peace and all the other people who are joining hands in friendship around the world. That's a good sign of recovering health in us."

Menninger masterfully made his peace point Friday night, in response to a speech by Sen. Robert Dole (R-Kan.), presented before 1,000 people at Washburn University of Topeka as the second in the Karl Menninger Community Lecture Series. Dole--who turned 60 on Friday, the same day Menninger turned 90--had praised the psychiatrist as a "prophet of prevention" and advocated private and federal cooperation in caring for needy children.

Menninger then expressed admiration for Dole's "great responsibility of representing the people" and asked, "How do you know what the people want? . . . Well, they have to tell you . . . I want you to know I'm against handguns. I'm against missiles."

The audience broke into enthusiastic applause. The conservative senator broke into a pained smile.

Menninger's current crusade against nuclear armament arose--naturally enough for a psychiatrist--from a dream. It occurred during his 1976 operation to have a brain tumor removed, an experience he described in a 1978 "Living Self-Portrait" he was asked to paint, verbally, by the Smithsonian Institution.

"I can't quite reconstruct it, but in some way there seemed to be a division in purpose as to whether they should save me or save the research. There seemed to be some kind of reprieve, and I was to be allowed to live four more years--but not idly.

"Suddenly I realized that I had been getting well but the world had not. There were dragons all around. Things needed to be done; dragons needed to be killed."

This strong sense of vocation is largely responsible for Menninger's longevity, says his wife of 41 years, Jeanetta Lyle Menninger, who gives her age as "a few years younger than Karl." "Having something to do and doing it has a great deal to do with the process," says the even-tempered former editor who coauthored "Love Against Hate" and married Menninger after he divorced his first wife in 1941. (Menninger has three children by his first marriage and an adopted daughter from his second.)

"Karl is a workhorse with an enormous reservoir of self-discipline," says foundation educator Prof. Paul W. Pruyser, coauthor with Menninger of "The Vital Balance." "I've often shared hotel rooms with him and seen him get up at 2 or 3 in the morning, reading papers and writing notes.

"After his surgery, he had a facial palsy, which made it difficult for him to speak out of one side of his mouth. He worked on that faithfully with our biofeedback people and physical therapists, daily for an entire year, with incredible determination to overcome the problem. Now you can hardly tell."

At one time Menninger was famous for his ability to simultaneously talk on the phone, open his mail and keep two secretaries busy while he dictated. "Nowadays," says Pruyser, "he's slowed down to a speed that is still in excess of many people's pace. But he does stretch out on a couch in his office for a half- hour or so, which the secretaries guard as a holy moment."

"Dr. Karl is not a coffee break kind of guy," says his longtime assistant Laura Fisher. "There's no idle time in the day." Menninger and Fisher usually bring lunch and work straight through. (Menninger's favorite is peanut butter on whole wheat with a piece of fruit and a bite of chocolate.) And wherever he goes, he moves fast.

"He travels," Fisher says, "to arrive."

This sense of urgency appeared fleetingly and poignantly throughout the celebrations. "He's a psychiatrist immensely sensitive to the ambiguities inherent in every situation," said his colleague Holzman. "He is, after all, 90 years old."

One such moment occurred during one of the weekend's many gift presentations. "Typically when Dr. Karl ends a meeting with us, he says, 'There wasn't enough time to say everything I wanted to tell you,' " psychiatric resident Richard Winer said when presenting Menninger with a framed photo of one of his psychiatry students. "He always wants to give more and more."

As a teacher, says his nephew Dr. Roy Menninger, a psychiatrist and president of the foundation, "Dr. Karl is provocative, challenging and sometimes upsetting. He often shakes students out of passivity. He has no use for yes men, and he's always been hard to please.

"But he exemplifies the Latin root of 'education'--educere, which means 'to lead out.' What he does is help people open doors."

About 10 years ago the Menninger Foundation's former archivist Verne Horne asked Dr. Karl what he wanted on his tombstone. "He said, 'I hope you will see they say I'm a teacher,' " recalls Horne.

"But he is also a student," Horne adds. "He grows constantly. He's always learning something new and starting a new collection--now he's into poetry and polished spheres. He's got an eight-track mind that comes at things from a unique perspective. And he's got an endless fascination with life."

What does Menninger want for his 90th birthday?

"I could use some handkerchiefs," he jokes. "No, the gifts embarrass me. I don't need anything."

Except some intangibles like a pardon for imprisoned Guatemalan physician Grabiola Brooks. "May I be so bold," he recently wrote President Gen. Efraim Rios Montt, "as to say that I could receive no more honored gift on my birthday than the news of your full pardon of this woman."

On July 11, 1952, in a tribute to his father on his 90th birthday, Menninger said, "Each one of us could say that our highest ambition can be only to reach the age of 90 with our vision as undimmed as his, our purposes as unchanged, our affection for God and his creatures as unswerving."

When reminded of that ambition this past weekend, Menninger quickly said, "My father was a much better man than I am. He was a Solomon who never got short tempered like I do. He was good to everyone."

Then after a moment's reflection, he quietly added, "I think he'd be proud of me. I am pleased that everyone remembered. Like the Psalms say, 'My lines have fallen in pleasant places.' "