Peter Kreitler was, he thought, a happily married young minister busy in the work of his church. But "one warm spring day" several years ago, "I began to realize I was falling in love" (with a parishioner who had come to him about problems in her marriage).

"It brought me up short," he says.He had counseled many church members involved in extramarital affairs and was well aware of the pitfalls. But here he was, a clergyman married to "a beautifuly and talented woman" and the father of two children, headed toward a liaison of his own.

"I realized this can happen to a normal person, that I wasn't immune, that no one is."

At the same time, during "my infatuation and my withdrawl from my family," his wife began to see another married man, "someone we both knew and respected." When Kreitler confronted her, she acknowledged that she, too, was beginning to fall in love, prompting him to confess his own involvement.

At this "perilous" stage of their marriage, they decided to defuse their outside relationships -- aided by the fact they both had remained sexually faithful -- and to begin working slowly toward "a satisfying reconciliation."

This personal threat to his marriage combined with the infidelities he heard about almost daily in his counseling "triggered an anger at my inability to help prevent this type of marriage dissolution from happening." It led him to develop a workshop on dealing with affairs "before the fact" and to write a book (with journalist Bill Bruns), Affair Prevention: Specific Techniques That Can Strengthen and Protect Your Marriage (Macmillan, 212 pages, $10.95).

Now 38 and associate rector of St. Matthew's Episcopal Church in the upper middle-class community of Pacific Palisades, Calif., Kreitler is realistic about his efforts to curb extramarital affairs, which he sees as "a national epidemic."

"I am going against the tide," he says.

Our society, he believes, tempts couples into affairs in many ways. We refer to them as "having a fling" or "fooling around," which sound less reprehensible than "adultery." In marriage, we have high expectations, and if we don't get it all, we turn to someone else.

And, at least in the first blush of love, affairs can be fun and ego-boosting. Your spouse may take you for granted, but a lover doesn't. "They're marvelous at stroking. In an affair, the great turn on is to go out and tell each other how senstive" you are to the other's feelings. Sometimes affairs can lead to a happier life.

Ours has become a society of "disposable" marriages, says Kreitler. When things get a little rocky -- and they do in most unions -- "our culture has given us an okay to bail out. People are in their second, third, fourth, fifth marriages and looking for the next.

"We build in an obsolescence in everything we make, and we apply this to human relationships."

Affairs can happen anywhere, he points out: Between family friends and neighbors ("Falling in love with our friends ruins a good friendship"), over a cup of coffee at work, on an out-of-town trip, with a former flame not forgotten, with your doctor, lawyer or other comforting counselor. Some married men (and a few women) are simply out "scoring" for the sake of their pride.

But, says Kreitler, "I think very definitely that marriage is going to survive this crisis of not taking it seriously right now. Really being committed to one person is the most satisfying of relationships," and the longer it lasts the more deeply satisfying it is.

Despite the enticements, affairs frequently turn our painfully. Parishoners show up asking Kreitler, "How do I get out of this?" A years'-long marriage they actually cherish is being destroyed. The pain strikes not only the lovers, but their spouses, children, friends and relatives.

"I'm constantly reminded," he says, "that affairs do have an impact a lot wider than people presume." One distraught woman had just told him about a close friend who had asked her to care for her children over the weekend. When she asked why, the friend replied: "So I can go off with my lover."

Says Kreitler, "This now involved her in the friend's duplicity. What would happen if the husband found out, if the kids knew?It's a lot more complicated."

Perhaps the hardest thing about an affair, he finds, "is having to live with the lying. That really hurts people."

How do you prevent an affair -- either your's or your spouse's -- from breaking up your marriage? Kreitler suggests:

Be aware that it can happen to you. "To presume you have a happy marriage, and not check it out -- by communicating, keeping in touch with where you are -- is a danger sign." Ask each other: "Is our marriage happy? Are our needs being met?" If they are, he says, "temptation isn't there."

Develop a prevention mentality. "You have to have the intention " to have a successful partenership. People too often "aren't willing to pay the price for the marriage to work."

Decide on what principles you will live by: "What's important to you." And then "Take responsibility for your own life."

Be aware of your own temptations. Affairs won't happen "if someone says no."

Encourage extramarital friendships -- "Even in the best of marriages, there is a genuine need for other male-female relations" -- but don't go beyond friendship.

Develop a "wedding" vocabulary with your spouse instead of one of "divorce."

That's the way new lovers converse.

Create an affair-proof climate in the home. This involves the wide range of things that lead to a happy marriage: communication, romance ("shower together regularly," dine by candlelight), laughter ("Don't take yourself too seriously"), mutual respect.

Appreciate the ordinary in your spouse: "None of us is supermen or women. We're oridanry."

Pay attention to the "ness" needs: "Kindness, goodness, closeness, togetherness. They're important."

If you discover your spouse in unfaithful, don't rush, Kreitler urges, to the divorce courts. Obviously, the affair has thrown "a monkey wrench" into your relationship, but "if you really love your spouse, you can build from an affair that has come to light."