"I had a pal get married, and you lose them," said Ray Eliot.

"They don't have as much time for single friends," lamented Eliot, the owner of an auto dealership, who is divorced."The relationship can be maintained, but it's scaled down. You can't replace it. You just keep yourself busy in other ways. It's a loss, no question about it."

Even if they haven't married - just become a duo in some unofficial sense - many couples seem to leave behind their longtime friends who are single or divorced.

Some couples feel less need for an extended family of friends once they have established a nuclear family of their own. Others assume their single friends are continually busy. And still others simply find that they no longer have much in common with their former peers.

The tendency for marriage to force friends apart may not be universal, but it is an old one. Robert Louis Stevenson wrote an essay deploring the effect of marriage on friendship in 1912.

"Marriage is terrifying," he wrote, "but so is a cold and forlorn old age. The friendships of men are vastly agreeable, but they are insecure. You know all the time that one friend will marry and put you to the door . . . So, in one way or another, life forces men apart and breaks up the goodly fellowships forever."

David Olausen was a musician for 20 years before beginning his present career as a packaging designer. Now 38, he is married, with a 2-year-old daughter, and an admitted "homebody." Still, he mourns his dwindling friendship with one of the bachelor members of his band.

"I usually go over to his house and check up on him; it's becoming infrequent though," Olausen admitted. "He's still being wild and crazy while I'm being daddy at home. I am a little sad those days are gone, but he's kind of lonely now. He wishes he was me, he says I have something to come home to, and I kind of wish I was him.

"I'm happy as a lark, my daughter makes my heart go thump-thump, it's the best feeling in the world. But at times I look back and think how much fun it was to be without cares, worries, wild and crazy."

Pepper Schwartz, a professor of sociology at the University of Washington who researches family and friendship, says the issue that divides former friends is not marital status but children.

"If you have kids, you simply don't have enough available time, and you spend time with your children that you would apportion elsewhere," she said.

"Singles simply can't understand how much identity people have with their children. They are thinking `how dare you bring the kids along! I want you, not your kids.' The parents see kids as extensions of themselves and you don't. It's not just that married people with kids withdraw, but they feel friends withdraw from them or set conditions they cannot or will not meet. It's a combined effect from both sides to mitigate interaction and intimacy."

Whether the friendship survives children, said Schwarz, depends on a number of factors, including how long the friends were single.

Longtime singles often savor the pleasures of adult relationships with people who have no children. Those who married young may never have known a world of singles beyond college.

Schwarz recommends that parents not require friends to accept their children and that singles try to understand the exigencies of parental schedules.

While we are often pressured to marry, social anthropologist Robert Brain says there is little pressure in modern western societies to remain longtime friends, even in the face of one friend's marriage.

"From late childhood onwards the frank friendships of the playground are not encouraged and are even replaced by a feeling of shame and guilt towards very close friendship, which seem to derive from our puritanical attitudes to homosexuality," he writes in "Friends and Lovers" (Basic Books, $10.95).

Nevertheless, many people try to sustain friendships beyond marriage.

Minneapolis film and video producer Gary Tassone, 39, who is single, says he makes an extra effort to stay in touch with friends who marry. It's not always successful.

"The obligation to maintain the friendship is chiefly on the single person's shoulders," he said. "The married friend has something new in his life and needs to deal with that and the realities of being married. I try to involve him, but I have to admit generally things are different - in my experience, the friendships very seldom remained the same. And if they can involve me in their lives in a way that works for them, that's great. If they can't, it's time to move on."

Those who pick their friends carefully and work at maintaining them seem to survive life's transitions - mating, marriage, children, divorce.

Mary Meehan, vice president of marketing licensing for The Lazear Agency Inc., is single but still enjoys the company of a number of married friends.

"I feel really fortunate to have the kind of friends who really work at maintaining a relationship, whether their situation changes or not," she said.

"They make a point of continuing to include me . . . As a single person, your married friends become a vital part of your life, you need the emotional support from them that most people get from a spouse.

"It's not only rewarding, but I get to take part in important experiences they have, like marriage and babies. It makes my life as a single person even more fulfilled. I get the best of both worlds. "