Stepfamilies in the United States number more than 25 million--or about one out of every seven. But these household regroupings often are viewed as aberrations of traditional homelife.

Even as more couples bring children from former marriages into new partnerships--about 1,300 new stepfamilies are established every day--few norms or guidelines exist on how to make them work.

Many stepfamilies try to reconstruct their original family arrangement, says California psychiatrist John Visher. "But that's impossible. Subsequent families are structurally and emotionally different from first families."

Visher and his wife, Emily, a clinical psychologist, spoke at a conference on family systems at the Psychiatric Institute Foundation in Washington. They are the co-authors of How to Win as a Stepfamily (Red Dembner, 196 pages, $13.95). The couple, who are now in their sixties, each brought four children to the new family when they married 22 years ago.

New York writer Elizabeth Einstein, both a stepchild and a stepmother, adds that failure to recognize the special dynamics of stepfamilies--built on the loss of spouses, parents and dreams of happiness ever after--can result in chaos. She is the author of The Stepfamily (Macmillan, 210 pages, $14.95), which began as a testimony for "all of the thousands of poor pitiful stepchildren.

"I got a lot of validation of this sorry Cinderella tale from other stepchildren I interviewed," says Einstein, now 42, "but my first draft of the book was rejected by my editor. She said I didn't have my own personal issues clarified.

"The rewrite was a catharsis in which I realized that pinning all my troubles on my stephistory was unrealistic. Actually I had a wonderful stepfather. The real problem was that as a child I was never allowed contact with my biological father."

As the eldest of five children, Einstein had been especially close to her father, doing everything with him, she says, from feeding the chickens to visiting local bars. He left when she was 8 years old, and by the time her mother remarried two years later, he had been shut out.

"I was devastated," says Einstein. "I wore all of these labels like 'unlovable kid' and 'abandoned,' and I blamed this incredible pain on my 'wicked' stepfather. I kept thinking that if only I had been a better little girl, my father would never have left."

Einstein's invention of her own rationale for her father's departure, say the Vishers, is a common reaction of children who are given no other explanation.

"It is a folk wisdom that children will adjust better if all contact is cut off from the divorced biological parent, but that doesn't work in most cases," says John Visher, who considers it important for children to maintain some contact with their other parent.

"Even if the other parent is a real rat, children need to have firsthand experience of just who this person is. Visits can be arranged with others present, such as at a grandparent's house, and it gives children a chance to make their own assessment without building fantasies."

A child's tendency toward "magical thinking" can be counteracted with a full explanation of what is happening, say the Vishers, "but kids often go to bed at night and wake up in the morning to find Dad gone. There is no attempt to warn children or to say we still love you."

It is also important, they add, for someone to listen to and understand a child's feelings of sadness and anger. While the adults are experiencing the "pink cloud" of just being married, children are at the opposite end of the emotional pole. They are not only grieving the dash of their hopes that their parents will be reunited, they are also having to share a parent with someone else.

Another common pitfall is venting hostility for the divorced spouse in front of children. For years, Einstein heard a litany of what her mother considered were her father's failings, but what her mother didn't realize is that the effect on Einstein was to make her think, "My father is part of me, so if he is rotten, part of me is rotten, too."

In an attempt to exorcise these negative feelings and to reestablish contact with her father, Einstein called him several years ago and agreed to set up a meeting.

"I canceled our date three or four times before I realized I was terrified that he was going to reject me again. I finally did go, and I learned that I love him because he is my father, but my real father is my stepfather. He is the one who stood by me. It took all of this time and writing a book in order to figure that out."

Einstein has also experienced the repercussions of unresolved relationships as a stepparent. Her second husband became estranged from his first wife which, she says, "signaled me to take over. I had two sons, and I always wanted a little girl, so I tried to make my two stepdaughters my own.

"What this really meant was that I tried to change my stepdaughters. They were tomboys who wore cutoffs under their dresses, and I went out and bought them all these frilly and lacy things, which they hated. What I didn't do is work at the important things, like accepting the fact that they were pretty neat kids."

As the two girls reached adolescence and expressed interest in contacting their biological mother, Einstein helped them, recognizing the same feelings of rejection she had experienced. But what she couldn't do at that point was share her own history.

Reunion between the girls and their mother kindled jealousy in their stepmother and resentment that "I couldn't have an exciting job too, because I had to rear her kids." Einstein also was afraid the girls' mother would someday try to take them away.

The Vishers advocate some form of joint custody as one way of mitigating feelings of loss and abandonment. "Parents worry that children can't handle the cultural shock of moving between households with different life styles and different rules. But children usually are able to adjust as long as each parent respects the other's parenting rights and separates the hurt of their ex-relationship from the children's need for an ongoing relationship."

While the cross-relationships in Einstein's family and others may not be as carefree as the antics of, say, the Brady Bunch, they have some rewards.

"Stepfamilies," say the Vishers, pointing out the positive side, "offer a lot more adult models to choose from and more richness of experiences. If you don't have to give up a biological parent, adding stepmembers can seem like a gain."