Susan Kulp may deserve some kind of award: She has been a stepmother twice -- to a total of five children. Her first encounter with stepmothering, which began when she was 23, she remembers as "a breeze." She was young and a schoolteacher. His three children lived in Ohio and visited them in Washington only on vacations. "It was like summer camp," she says.

After 11 years and three children of their own, the marriage ended. In 1981, she married a man with two daughters (ages 10 and 13) who share the house on weekends with her three children (ages 13, 15 and 17). This time, at least initially, it was more like an armed camp than summer camp.

The experience is increasingly familiar to Americans, more of whom by 1990 will be living in stepfamilies than not, according to the Stepfamily Foundation in New York. And as the number of divorces and remarriages increases, and women postpone marriage to their late twenties or thirties, more will find themselves in the position of stepmother.

Some, such as Susan Kulp, bring children of their own to the new marriage. Others are "weekend" stepmothers -- their husbands' visitation rights determining when they see the children. Then there is the "instant parent," who, perhaps because of a death or a nontraditional custody decision, takes on stepchildren full time.

Sometimes, as with Kulp's family, the first sign of trouble is scheduling, just trying to figure out which child should be where.

"We each kept our individual visitation schedules when we got married," Kulp recalls. "We were terrified the kids would feel abandoned, and also we wanted some time indivudally with our own children. So picture this schedule: On Friday nights he picks up his children, and mine are there on alternate weekends. His go on Saturday and come back Sunday and Monday."

In addition, things had to be arranged to accommodate the schedule of Kulp's husband, a cellist with the National Symphony. Her ex-husband, who lives in Washington, sees their three children on alternate weekends, and one night during the week. One of the three children stays with him an additional weeknight. Her husband's ex-wife, who lives with her second husband in Alexandria, has custody of the two girls, but their father has regular visitation rights.

"We had incredible Friday night dinners," she says. "Everybody would explode. For several months, at least one person would blow up and leave the table. One night everybody blew up except my husband and me -- right after another, five children! It was just the tension. . ."

Kulp, now 44, is small and compact, with a well-developed sense of humor. She has a judiciously maternal air, no doubt honed through years as a teacher as well as a mother. Blending the two families hasn't been easy, but the household is now on a fairly even keel, a hard-earned and still tenuous equilibrium.

"There were so many fights that were unconsciously designed to split us. They want their natural parent, and they don't want to share him . . . I noticed that on Mondays when his kids were there, my kids just needed me for every little thing. They would get along fine if we weren't there, then as soon as we arrived they'd start fighting."

But she always believed it was mostly a question of time. "If you didn't believe that you'd just die. We also had this concept: We had to stay together in working this out. We might fight ourselves, but we had to be very tight in front of the kids, and they would just have to come along."

After the first year it was obvious that keeping so many schedules didn't work for anyone. Now her stepdaughters usually come on the same weekends that her children are home, and she and her husband have a child-free weekend in between. They went to a counselor, who helped them to work as a team, "to know when we are exhausted" and to deal with their frustrations with her ex-husband. Chores -- those eternal irritants in every parent-child equation -- were established as well.

Kulp reacted to her stepdaughters at first with a combination of exhaustion, concern and a feeling of helplessness. "I didn't have a role . . . I'm not needed by them in the way I'm used to being needed."

But now she feels her relationship with the two girls is developing well. She was delighted recently when 13-year-old Katy picked her to visit on her school's career day.

"It's terribly hard on all the kids. They have to spend so much time satisfying the needs of the different parents, they hardly have any time for themselves.". "You just have to be careful what you say or do. You bite your tongue a lot. Especially right after you marry, it's bound to be chaos. Especially with teen-agers."

A year ago she won a free family portrait at a local store. All the kids were summoned for the outing. But her second daughter balked. She didn't want to get cleaned up. She didn't want to go. She thought it was a dumb idea. Nonetheless, she was forced to join the group, and today the portrait, with all five kids and the two parents, hangs on the wall. Everyone looks clean. And everyone is smiling.

It didn't work out so well for Renee Burrows. Two years ago she and her second husband separated after 11 years of marriage and trying to "blend" her two sons and daughter with his two daughters and son. Although the children were not the cause of the breakup, she says they caused a "tremendous amount of tension" that exacerbated the marital difficulties.

There were numerous problems, says Burrows, who returned to her home town, Boston, when she left her husband in Florida. Only one child, her youngest son Steven, lived with them, but the others came home from school regularly.

The two 13-year-olds, her daughter and his, fought constantly. "It could be over anything. My stepdaughter would say something like, 'This is my father's car, so you can't ride in it. And my daughter would say, 'Well, my mother is cooking dinner, so you can't eat.' It was a mess."

She felt her husband did not devote enough attention to Steven and was too tough with him. There was also a substantial difference between the two sets of children: hers were raised in an eastern, liberal, intellectual atmosphere, encouraged to speak their minds, go to the best schools, and achieve. They thought their stepsiblings were less cosmopolitan and looked down on them.

Her husband "was very upset that I didn't love his children as much as mine . . . I did see his children as second-class citizens; my kids were more colorful, more interesting . . . one of the biggest crimes I committed with my stepchildren was that we never really sat down and talked about an overall plan before we got married -- what he wanted from me, what I expected -- we never resolved things, we just let it happen."

Much to her surprise, the stepchildren said they were distressed at the breakup.

The big surprise was the other stepdaughter, with whom she had never gotten along. "She came for a four-hour visit, and then I got this beautiful letter. In it she said that I was her role model, and that she had given me such a hard time because she was jealous of me . . . I felt bad, because I felt I had not been very perceptive. Maybe I could have done a better job . . . I never felt like these children were my children."

Weekend stepmothers are locked into a particular dilemma: The children are always visitors, their relationship with father and stepmother framed by the rules of visitation and custody.

The weekend can become a capsule of torment; the effort to impose normality on an artificial situation creates numerous problems. The father, who often misses his children far more than our mother-worshiping culture acknowledges, may try to provide nothing but bliss for their visiting children; others act as though the two weeks between visits were a merely a pause in their real life -- with him.

Some couples put their own lives on hold when the children arrive, refusing social engagements and postponing chores. As the children grow and have social agendas of their own, a new set of resentments can crop up as Dad and stepmother are ignored in favor of dates and parties.

If the children have their own rooms in their weekend home, the rooms are mostly empty, a mute reminder of the diminished place the noncustodial parent has in his children's lives. If they have no room, the children often feel they have no place either.

Two weekend stepmothers illustrate typical experiences. Both are 34, both are professionals, both married late. Both requested anonymity.

One, Sarah, (not her real name) has a 2-year-old of her own and two stepsons, who were 8 and 10 when she met them five years ago. The relationship seems excellent; they like and respect her, and occasionally express it. But basically, she says ruefully, they are just "a fact of life, like brushing your teeth."

The two boys live in a neighboring suburb with their mother and stepfather, who are generally cooperative and amicable. The hardest part about being a stepmother for her, she says, is being a bystander in the relationship between her husband and his sons.

"It's difficult to see detrimental things happening and not know what my role should be," she said. "I bite my tongue a lot . . . My husband feels guilty about not being a full-time father to his boys, but he is not prepared to change his behavior. I tend to compensate for him by spending more time with the younger one because we have more similar interests, and I think I have had an impact on him because of that.

"Basically they are visitors. I don't feel anything more for them than I do for my best girlfriend. I really do not get very involved in their lives."

For Sharon (again, not her real name), problems with her husband in some ways were crystallized by the difficulties with her stepchildren. Eventually she sought professional help.

Her husband's divorce was not amicable, and his ex-wife is bitter even six years later. The children were 13, 10 and 8 when Sharon met them, and their mother's disparaging remarks doubtless affected their early, negative relationship with their stepmother. The stepchildren were polite, well behaved -- and traumatized by the divorce.

"I was the sort of person who lived in a one-bedroom apartment so that I wouldn't have to buy any furniture," Sharon said. "My first thought after the wedding was, 'Oh no, not only am I stuck with him for life, but I'm stuck with them too!' "

Only the middle child, with whom she had an immediate although tentative rapport, attended their wedding. None has spent the night since she moved in with their father. The oldest, a son, ignored her -- politely -- for several years.

"They have warmed up gradually," she said. "What has really changed is my attitude." She describes herself as initially "immature and self-centered," unable to really get involved in the aspect of her husband's life that he cared most about -- his children.

"The way I saw it, normal was when it was the two of us. Normal to him was that he had three kids -- and I wasn't sharing that."

When the children ate "her" food, she resented it. When they came to visit, she counted the hours until they left. The presents she bought were from a list the children gave their father. She was angry that her husband canceled all social engagements when they were there, and that his insistence on seeing them every Saturday meant they couldn't go anywhere on weekends.

Now she doesn't care what they eat, takes her stepdaughters on shopping expeditions and buys them surprises. She makes an effort to get them talking and one day realized, with a start, that she was a role model -- especially to the girls, whose mother never worked outside the home. She has even found a useful role as confidant and mediator in the occasional misunderstandings between parent and child.

"It's been very hard," she said. "I wish we had talked about it more before we married. And when I realized I was in trouble, I should have gone for help sooner. I feel the lost time, and the lost experiences . . . I get a perspective on life from them that I wouldn't have otherwise. And I give a lot too."

At worst, the stepmother has all of the responsibilities of motherhood and none of the authority or natural affection. At best, the relationship can be an unusual intergenerational friendship, enriched by even a limited triumph over adversity.

Martha Pedrick took on her stepdaughter Sydney five years ago, when the child was 12. Pedrick said everyone agreed that the mother's rural California home did not offer Sydney the educational advantages of an area like Washington. Pedrick was 31, a lawyer.

"I was apprehensive. I knew she had a good relationship with her mother, and I didn't want to interfere with that. I thought I would be a sort of big sister, that our best arrangement would be to be friends. That didn't work."

The reason that didn't work, she discovered, is that friends don't get angry about bad grades, or tell each other to practice their music. And friends don't have a sexual relationship with the father, which can be a source of subterranean jealousies -- particularly if the stepchild is a girl.

In Pedrick's case the relationship proceeded without major traumas, but with plenty of fights.

"My greatest fear at first was that if I disciplined her or yelled at her, she would think I didn't love her," Pedrick said.

In August 1983, she had a baby, Rebecca, and since then has stayed home. On the whole the family has expanded smoothly, but there are still occasions when Pedrick is reminded of her place.

"From the beginning there was a lot about me that John wanted Syd to experience: stability, a strong sense of family . . . The other side of that is that he is very involved with her. He feels that he has so much invested in her that he has to have his say first. If we're having a family discussion and I start to say something, he will put his hand on me to stop me. It's as though my point is not as important as his. Since Rebecca was born, if there's something going on with the three of us and she needs some attention, it's always me who is expected to go to her."

Lynn Bair was 24 when she met Steve, the man she would marry four years later. They were introduced in his office in New York City, and the first thing she noticed was a picture of his two children, then 6 and 4.

"I always did like the children," she said, sitting in a pleasant living room in a new Alexandria town house. "They provided a dimension in my life that was missing as a single woman. I liked fixing birthdays for them, and that sort of thing."

Lynn and Steve married in 1975, and saw the kids frequently. When they moved to Washington in 1978, his son, Tom, moved with them. Two years later she had a son, Ned, and less than a year later her stepdaughter, Katie, came to live with them also.

She speaks with the air of one who has been through the wars, one who within a short time became the parent of an adolescent boy, a baby and a teen-age girl. The family is relatively calm after six years, but it hasn't been easy.

"I didn't realize how much it would change when they came to live with us," she said. "We'd never had disagreements before, because there was no occasion for them. When they didn't live in my house I didn't feel it was my prerogative to tell them anything; Steve handled all the discipline. Suddenly I was the one at home and if something came up during the day, I had to handle it. I felt hesitant, and I'd always think, 'Now, what would Steve want me to do?'

"Their mother's life style is vastly different from mine. She is unconventional, and I am very conventional.

The problems have been typical and agonizing. The summer her stepson got his driver's license was a disaster. "He thought that he had as much right to the car as I did," she said. "It was impossible . . . If we hadn't gotten another car I might be divorced by now."

Now, with the oldest child in college, and the second due to begin next year, Bair may have to return to work sooner than she wants -- leaving her own child in order to help support her stepchildren. "I'm determined not to be a victim," she said. "But if I have to go back to work full time I'll feel very martyred."

At the same time, she does not regret the children's entry into her life. And she prefers having them full time over the half-life of weekend visits. "We have some control over them, we have some chance to impart our values . . . And their relationship with Ned is wonderful; I wouldn't give that up for anything.

"I almost married a man without children. But I chose Steve. I guess you could say that I knew what I was doing."