She has seen it all, Ann Landers, seen it all. Desperate in Duluth, Lost in Austin, Juiced in Houston, all the five-and-dime and million-dollar ways in which people do badly or feel badly or find their lives translated into parodies of the way it was supposed to be.

"Nothing surprises me anymore," she says flatly. "Nothing."

A reader wants to know, then, what human nature looks like after the surprises are over, whether the giver of advice has her own dark moments of doubt, whether there are any of those dark nights of the soul, those 3 o'clock in the mornings that F. Scott Fitzgerald had written of.

"Fitzgerald," says Ann Landers, "was a very unhappy man, definitely unbalanced and an alcoholic. I've never had a dark night of the soul in my life."

Ann Landers, who has been writing her column for seekers of comfort, advice and mercy for 23 years, still talks in the cadences of her Midwestern girlhood, she talks in the declarative sentences of the profession, no musings, no ponderings, no pensive pauses

"I've done my best," she says. "I'm good, but I'm not afraid to admit when I'm wrong. I see things through the prism of my prejudices - that even the very best of "people get lost in this life."

Ann Landers is not lost. She has just been to the White House and she is on her way to a talk show. At the White House yesterday, she talked to Jerry Rafshoon, the president's media adviser, about raising children and she gave him a copy of her book, "The Ann Landers Encyclopedia, A to Z."

She will not say whether she talked to the president. Ann Landers does not answer every question asked of her. She does say this: "I'm a very ardent supporter of President Carter. I'm not suggesting that I'm an adviser, but we do touch base. I do have my hand on the pulse of the nation."

She does not want to talk about her column, she is tired of talking about her column. She wants to talk about her book. It was her friend Mary Lasker's idea.

"We just sat down one day and listed all the subjects we thought troubled people." she says. "Marriage, divorce, just coping - a lot of people don't know how to get through the damn day anymore. Masturbation, cirrhosis, snorting. How do you get rid of a drunken dinner guest? How do you tell a child about death? People don't even know where to get help these days - that in itself is extraordinary."

She wrote some of the chapters of the book herself and enlisted a battery of experts including the late Hubert Humphrey and Margaret Mead, to write others and personally called all the hot-line numbers listed, in her book pretending to be suicidal or depressed or whatever was required to make sure that there weren't "any wrong numbers or nutty religious groups."

And she still gets a thousand letters a day to answer some asking for her help (the majority talking about the problems in their marriages or their children), some asking for her approval ("He beats me, Ann, and he drinks too much and I lost a tooth, but don't tell me to leave him"), ("when I've been too hard on Hopeless in Hackensack.")

The ones that seek her approval are the ones that brings a bit of surprise to her eyes. On the talk show, she takes a few telephone calls from the people watching her. One caller asks her about gay relationships. "It's all right by me," says Landers, who is 60. "I have nothing against it."

But after the show is over, she wonders, "Why do people feel they have to ask me if they should have a gay relationship? They don't need my approval. I can't see why so many people look to me as some sort of oracle."

She finds it "a little heavy," this responsibility to thousands of faceless people who write to know what to do or if what they are doing is right. "I don't like to play God," she says, checking her makeup before the pictures are taken.

Some of the opinions preferred in her book are different from those that might have been offered if she had written it years earlier in her career. The loss of virginity before the recital of the marriage vows seems not quite so horrific if the circumstances are right although living together is still "a bummer." Divorce, however, is not. Some people just really shouldn't have to stay married," she says. "If a man's got another woman, or a woman another man, what can be done?"

She herself surprised thousands of her readers by announcing in her column in 1975, that her own marriage of 36 years had broken up. "How did it happen that something that was so good for so long didn't last forever?" she asked in that column. "The lady with all the answers does not know the answer to this one."

The talk-show telephone callers ask Ann Landers whether 12 is too young for coed dances ("Dancing can lead to other things") and what to do about a suspect neurologist's diagnosis ("Get a second opinion"). She is a bit exasperated by them, they're not the sort of really challenging questions that would have made first cuts if she had had anything to say about it.

Peter O'Toole wafts in for his turn on the talk show, trailing cigarette smoke and a small entourage and looking rumpled and sleepy and a bit bemused. They greet one another and seem rather mystified by whatever cast of fate or circumstance had tossed them in the same room together. Then Ann Landers is asked to meet a 17-year-old girl who has just run 2,000 miles for epilepsy, and that makes a lot more sense.