The sexual bond between husband and wife is so imbued with symbolic and mystical properties that if it is altered, both partners can be devastated.

Certainly, this applies when infidelity is discovered. And when infidelity is the result of a homosexual affair, an extra layer of strain is added to an already stressful situation.

"I can handle it, whatever it is," says Claire in the movie "Making Love." But when her husband reveals his homosexuality, she cannot.

It is impossible to know how many couples are involved in similar situations. But when the address and phone number of a Washington area support group called Straight Partners was printed in Ann Landers last year, the group got 1,000 letters in the first month. Altogether, they have received about 2,500.

For a while, Straight Partners believed they were the only such group in the country. But more recent letters show that similar organizations have sprung up in New Haven, Conn., and Milwaukee, Wis.

When gays decide to tell their spouses about their homosexuality, they can usually expect to receive support and encouragement from the gay community. But heterosexual spouses, as a rule, have had few places to turn.

"Most people don't tell their friends," says Ann, a psychologist in her 40s, who has been one of Straight Partners' most active members since it began about 3 1/2 years ago. Her name, and others in this story, have been changed.

"For one thing, they think you're dehumanizing yourself or compromising yourself if you try to stay in the relationship. There's this feeling that somehow the wives drove their husbands to it. Even some parents will accuse their daughters-in-law of not being good enough."

All of this, of course, can lead to feelings of guilt on the part of straight partners, to fears that they must have done something wrong.

"Sometimes it only takes one phone call," says Gloria, 36, a graduate student in psychiatric social work and another active member of Straight Partners. "All they need to know is 'It's not my fault' and 'I'm not the only one.' Once they get that out of the way, then we never hear from them again."

Based on her experience with Straight Partners, Ann describes other emotional reactions she feels are common to spouses who discover their partners are homosexual. "Usually there are feelings of depression at first, followed by a period of grief or mourning over the loss of something that can't be replaced." Often these feelings are combined with "intense feelings of betrayal, of being used as a cover."

Feelings of anger also well up. "My husband went through a period where he wanted everybody to know he was gay," says Gloria. "Gay is great and that sort of thing. He didn't seem to be sensitive to the fact that maybe I didn't want the neighbors to know. One day he even wore a T-shirt out in the yard advertising the name of a gay bar. It was those things that really annoyed me. I realize it was an important stage for him to go through, but it was the source of my greatest anger."

"One of the things that made me angry," says Kathy, a founding member of Straight Partners and now separated from her husband, "was that when we talked about our lack of sex he never gave me the real reasons. He would just say things like 'I'm frustrated at work' or whatever. At the time, I was angry that he didn't tell me sooner. But now that's kind of died away. We're still good friends."

Like Kathy, Gloria seems to feel no lingering bitterness toward her husband, from whom she is now separated. "I don't believe he married me as a cover," she says. "He tried every way possible to save our marriage. I respect his dedication to me and appreciated his efforts to try and change."

According to Adam DeBaugh, a lay official of the gay Universal Fellowship of Metropolitan Community Churches, and counselor of straight spouses and married homosexuals for six years: "Men generally handle lesbian wives much worse than women handle gay husbands. It's a greater blow to the male ego. Most of the men I've known about have reacted very angrily, especially where child custody is involved. A woman's anger seems to be more inwardly directed."

For some reason, men seem to seek support groups much less than women do. "Many men aren't able to admit what has happened," suggests Ann. "They're just not able to get on with their lives." Of the letters Straight Partners received as a result of the Ann Landers column, about one-third were from men. Only about four men have participated in the Washington-area group since it began.

Both men and women, says DeBaugh, 34, share a common reaction to the discovery that their spouse is homosexual: the feeling that somehow their marriage has been a fraud. "A lot of people ask 'What does this mean for our marriage? Have the past 10 years been a lie?' Naturally, the answer is 'of course not,' assuming the relationship has been a loving one."

Another question often raised, says DeBaugh, is " 'What is to become of me?' The straight spouse is usually not prepared to seek other relationships. The gay person has been building to the point where he is comfortable seeking others out. But the straight person has not been going through this building process."

At some point or another, says Ann, some straight spouses begin to question their own sexual attractiveness. One man, for example, paid a prostitute because he needed to know if he could function sexually. A woman, who had put herself through school as a go-go dancer, described how she resurrected her old outfits to see if she could arouse her husband. Still another woman told of seducing a man in her office because she wanted to know how it felt to be with "a real man."

Re-experiencing a heterosexual connection can be, for some, a great boost to self-confidence.

"It was an amazing revelation to find a man who got turned on to me," says Kathy, 38, an artist. "When you've been rejected for so long and then find a man who desires you, it's a great feeling. I had been sexually active before my marriage so I knew I had been attractive to men. But it was really exciting to find that again--and necessary for the ego, too."

How one learns of a spouse's homosexuality is, of course, critical.

"Those who walked in on their husbands having sex with another man are much more traumatized," says Gloria. Says Kathy: "Everybody goes into shock at first. But at least you feel like you're being treated humanely if you're told outright. Many people have found out by finding literature in the car."

Some men, says Ann, drop hints by "leaving membership cards to gay baths lying around."

In her own case, she had "lots of inklings" that her husband was gay, although he was not homosexually active during their marriage. "I knew he was using fantasy with things like books and magazines."

She recalls how one night when her husband, a doctor, was due to return from a business trip, she came home to find several messages on their telephone answering machine. "He must have stopped at every gas station along the way. Basically all the messages said 'Please stay up--there's something I want to talk to you about.'

"When he got home, he pulled up his sweater and placed my hand over his heart so I could feel it racing. Then he looked at me and said 'I want you to know I'm gay.' And I said, 'I know, I've known for a long time.' Then we both took off our wedding rings and talked for two hours." Ann was three months' pregnant with their daughter at the time.

For Tom, a 50-year-old professional from Northern Virginia, the discovery that his wife was lesbian came gradually. During the early years of their 10-year marriage, she began bringing home friends he thought were mannish in appearance.

"It bothered me," he says, "but when I would mention it she would just say 'Don't you think they're nice people?' A few years ago, she joined the Coalition of Gay Sisters and, well, that doesn't pretend to be anything else but lesbian."

About a year and a half ago, Tom's wife told him she thought she "might prefer women." But it is rare that they ever discuss the subject directly. "She's kind of vague," he says. "She just doesn't want to talk about it." Explaining how he married his wife "for companionship--it wasn't for sex" and admitting that he has had two affairs, he says he has no desire to separate, although he is prepared for the possibility that his wife might leave him.

Unlike Tom, 42-year-old Frank, an engineer--who describes his marriage as a "very close and loving one"--shared in his wife's discovery that she was physically attracted to women.

"When we went away to Greece," he says, "we had a young female tour guide whom we got to know and she sort of began flirting with Andrea. I didn't notice anything, but Andrea did. Something had been aroused in her and we weren't sure what.

"When we got back from Greece, Andrea started to spend more time with Marsha, a woman she works with. She was describing these feelings to me, how she felt an extreme physical desire for Marsha. She had never felt that before."

Frank says that, in a way, it's been a learning experience for both of them. "Now we can see how a lot of things fit together. We've done a lot of reading and have had good conversations with a priest who has become a good friend. We agree with him that if it's a part of you, it's okay."

When a married couple discovers that one partner is gay, there are many issues that must be confronted. How to tell the children? How to tell parents? Should the children meet the lovers? But the ultimate and perhaps most painful question of all is whether to stay together.

Some couples, of course, decide to split up immediately and others try to make a go of it. "There are very few survivors in our group," says Gloria, "but some of us have taken a long time (to give up). Those who struggled were those who had been committed to each other."

"My husband and I tried to keep our marriage together for two years," says Kathy. "We told each other we'd give ourselves time and make certain he really felt he was gay. When he eventually decided yes, he was, I knew I couldn't stay in the marriage.

"We were both so frustrated trying to pretend we were a normal married couple. We both wanted a monogamous relationship and neither of us found going out with other people very fulfilling. But he's much happier now that he's accepted being gay."

When couples separate, they often try to work out some type of co-parenting arrangement. Ann and her husband, for example, rented a house split into two apartments. "We bought two of everything--two cribs, two playpens--but it allowed our child to bond to both her parents and that was important to us."

Another benefit of this "upstairs/downstairs" arrangement, she says, was that it gave her and her husband time to divide their possessions and separate gradually.

For those who stay together, the open marriage route is sometimes followed.

"This can work for the straight woman, if she has a low sexual desire," says counselor DeBaugh, "but it is generally the gay man who has the problem. He usually begins to feel the need to stop the duality. It can go on for a time, but over the long run it doesn't work. There's still the sense of adultery there."

In a recent study of 18 San Francisco-area gay men, published in the Journal of Marital and Family Therapy, only one reported he was still happily married to his wife and actively homosexual. All had been married at one time.

"When the husband makes a full disclosure of his homosexuality to his wife after they are married," writes Frederick Bozett, the study's author, "divorce is the most common outcome."

Another way some couples have tried to keep the marriage together is to enter into a me'nage a trois.

But, according to DeBaugh, "The pressures that work on a three-way relationship are really profound." He says it is rare that such relationships endure on any long-term basis, although he is aware of one case involving two men and a woman that has lasted seven years.

As for Straight Partners, some members believe the group, for them, has served its purpose: providing support when needed. "I think," says Ann, "I've told my story enough times." Because key coordinators are sensing a need to "move on," as they put it in a recent letter to the membership, the future of the group is cloudy.

Perhaps in coming years, if there is more acceptance of the gay life style, the need for such a group will no longer exist, with fewer of these so-called "mixed" marriages occurring. More people would be spared the almost inevitable anguish that accompanies them.