For a writer of children's books, Judith Viorst knows a lot about grown-ups.

The author of the best-selling children's classic "Alexander and the Terrible, Horrible, No Good, Very Bad Day," and other works of fiction, poetry and social commentary, explores the essence of a successful marital relationship in her newest book, "Grown-Up Marriage."

Viorst will have a chance to elaborate on the subject at an upcoming lecture, to be held at the Osher Marin Jewish Community Center on Thursday.

Having herself survived more than four decades of wedded bliss, Viorst will surely have much to say — maybe too much.

"I remember going out with a non-Jewish guy before I got married, " Viorst recalls. "He said to me, 'You Jews: do you ever shut up?'"

Fortunately for her admirers, Viorst has long been a steady fount of scholarship, whimsy and insight into the human condition. She is the author of 12 children's books, eight collections of poetry and five books of prose, including the bestseller "Necessary Losses, Imperfect Control" and her comic novel "Murdering Mr. Monti."

Viorst's Jewishness has been a source of cohesion for her. "Being a Jew has a family aspect for me," she says in an interview from her Washington, D.C., home. "The family gathers here for the holidays. We know we are Jews, but I wouldn't say it has necessarily shaped my views on marriage."

Those views came about more by her steady powers of observation. Says Viorst, "I've written countless articles, talked to so many people about marriage, eavesdropped on so many conversations, I feel I've acquired a vast amount of information."

Her central message may be one that some married folks don't necessarily want to hear: Clean up your act, literally!

Says Viorst, "Married people think they can be their most unvarnished selves and still be loved. That's a fantasy. Without manners, charm or grace, life can get drab. If you bitch, burp or act in an inconsiderate manner, you do harm to the marriage. We can't think of marriage as the dumping ground for all the darkness of our life."

If that sounds like work, it is, according to the onetime psychoanalysis student. "Eternal vigilance is the price of a good marriage," says Viorst. "If you're not taking the pulse of the marriage, it's easy for things to get empty and disconnected. Gradually, we acquire a rueful tolerance of each other's imperfections."

Not that Viorst holds herself up as the perfect role model. In fact, she credits trial and error for the longevity of her 42-year marriage to political writer Milton Viorst.

"Choosing the person you wind up marrying requires a vast amount of dumb luck," says Viorst, "because it's impossible to know who we will become and who the other person will become."

Along those lines, notes Viorst, newlyweds often find themselves experiencing a touch of buyer's remorse.

"For young couples, there are surprises and shocks," she says. "There are qualities people instinctively don't reveal before marriage. It's bait and switch. Even if you know some of the not-so-wonderful things about your spouse, the information sits differently after you're married. You realize you have to put up with this the rest of your life."

Beating the odds thus requires a bit of foreknowledge, according to Viorst. "It's a tricky combination of honest and polite," she says. "We need to know how to communicate and to know when to shut up. Basically, you should apply the same tact with your spouse that you would with anybody else."

The changing mores of the past 40 years don't entirely sit well with Viorst. "My biggest regret," she says, "has been seeing casual sex elevated to such an acceptable degree, because I think sex is a really big deal. If you want entertainment go bowling."

Viorst is also not a huge fan of couples living together before marriage. "They break up at a much higher rate," she notes. "It's probably because people who choose to live together tend to be more untraditional. That same impulse makes them more comfortable with divorce."

Despite discouraging divorce statistics, Viorst still views marriage and family as the most worthy of institutions. "I see marriage as a third thing," she says. "Not mine, not yours, but this creation we build together, to which we owe certain obligations. To it you bring the finest strivings of the human heart."