''In custody battles no one wins,'' says Alan Lehotsky of Lexington, Mass., who is separated from his wife, Susan. They have already initiated a shared-parenting arrangement to care for their 6 1/2-year-old son, Steven. ''I certainly would not want to give up custody,'' says Mr. Lehotsky. ''And with sole custody, Steven would end up being hurt as much as Susan would.''
Mr. Lehotsky expresses the sentiments of divorcing couples who want to continue to share the responsibilities and everyday decisions regarding their children's upbringing. For the children, the hope is that shared-parenting arrangements can promote the feeling that both parents are devoted to them and love them.
Joint-custody agreements, which are often reached through mediation, sidestep bitter courtroom scenarios in which divorcing couples ''fight'' to ''win'' custody, with children often caught in the cross fire.
Although the shared-custody option was previously open to parents informally, before 1980 only six states had written it into law. Today, 28 states have laws either permitting or giving priority to joint custody when the judge finds it in the child's best interest.
Despite legislative changes, relatively few divorces have actually brought shared custody, with sole custody decreed in about 90 percent of custody cases.
''A divorce case is not meant to be a termination of parental rights,'' says James Cook, head of the Joint Custody Association, based in Los Angeles. Mr. Cook, who pioneered the California Joint Custody Act, believes children should have easy and continuing access to both parents after divorce.
Although studies observing joint-custody families indicate shared-parenting arrangements may be the preferred solution to a knotty problem, the custody debate is far from closed. Both sole-custody and joint-custody advocates emphasize the importance of considering each case separately, but they differ as to whether joint custody should be the rule rather than the exception.
''Joint custody is marvelous for families that can cooperate, but it's not a panacea,'' says Hugh McIsaac, director of the Los Angeles Conciliation Court, a division of the Los Angeles Superior Court. He sees a danger in ''well-meaning persons pushing the idea'' before couples are ready for it and believes more research is needed to determine the long-term effects of joint custody on children.
Critics of joint custody say couples whose differences are great enough to warrant divorce are not capable of cooperating to the degree necessary to make a shared arrangement work.
In some cases, however, divorcing parents are able to put their children's welfare above personal differences.
According to Mr. McIsaac, shared-parenting after divorce is a process that takes place over time, and parents must assume a businesslike relationship to make it work. ''The families I've worked with understand that and make the shift ,'' he says. ''When the parents are able to do that, it accelerates the process of healing.''
Ciji Ware, author of ''Sharing Parenthood After Divorce'' (Viking Press, New York), says one of the greatest strengths of joint custody is that it ''gives children permission to love both parents.''
Many judges and family professionals, however, are not convinced that joint custody is best for the children. They adhere to the argument for sole custody put forth a decade ago by psychiatrist Anna Freud, and by two Yale professors, Albert Solnit and Joseph Goldstein, who say the security of the child after a divorce is rooted in the care of one custodial parent.
From his previous work at the Child Custody Clinic at Stanford University, Dr. Stuart Berger, author of ''Divorce Without Victims'' (New York: Houghton Mifflin Co.), finds that parents are often desperate in the face of custody decisions. As an advocate of sole custody, he says, ''It's excruciating and painful, but the decision has to be made.''
According to Hugh McIsaac, the decision is particularly agonizing for judges faced with two competent parents who both want to take an active part in the life of their child. In these cases joint custody can be a feasible choice.
To date, studies of shared-custody arrangements tentatively point in its favor.
* Dr. Mel Roman, author of ''The Disposable Parent: The Case for Joint Custody'' (Holt, Rinehart & Winston, New York), concluded from a study of 40 joint-custody families that cooperative custody arrangements are in the best interests of the majority of children and should be presumed so by law, unless special circumstances indicate otherwise.
* The findings of a five-year study completed in 1979 by Dr. Judith Wallerstein and Dr. Joan Kelly of the University of California, Berkeley, revealed detrimental effects suffered by children who effectively ''lost'' one parent after divorce. Dr. Wallerstein believes that joint custody may not work in every case but that children do benefit from arrangements in which they maintain contact with both parents.
In practical terms, co-parenting arrangements are not always based on a 50-50 time-sharing principle. The schedules are usually more flexible, depending on the children's needs and the natural transitions in their lives.
Ciji Ware says the shared-custody arrangement for her 11-year-old son, Jamie, has changed three times in ten years. ''When he is 13 he may opt to home-base with one parent,'' she says.
Opponents say the two-household aspect of joint-custody arrangements can be confusing to children and precludes developing a sense of home. ''The core components of child development are predictability and continuity. It's not good to have children shooting back and forth between homes,'' says Dr. Berger.
Advocates of joint custody argue that children handle similar situations when attending boarding school or summer camps. The most important factors, says Ms. Ware, are that the children are loved and understand the ground rules in both homes.
Linda Bernstein, a mother who has been involved in a joint-custody arrangement for about two years, says sharing households demands a great deal of flexibility on everyone's part. Her two teen-age children spend three nights a week in her apartment and the rest of the week in their original home with their father.
''It's difficult for the kids because they still regard their [original] home as their primary place to live,'' she says. It has been especially trying for her 16-year-old daughter, who insists on having all her clothes with her and has a hard time dealing with the smaller space of the apartment. But she says her teen-agers still feel it's the best arrangement under the circumstances.