LIKE THOUSANDS OF TEEN-AGERS who are not married and who become pregnant, don't want abortions, and realize that they cannot provide a proper home for their children, Renee chose last winter to make her baby available for adoption. And like an uncounted but growing number of young women. Renee did not go the way of the traditional, closed adoption -- the adoption that has been called an eternal curtain of secrecy between biological and adoptive parents. Renee, a high school student in Traverse City, Mich., helped pick out her baby's new parents.

Once she chose them, she and they talked at length about the sort of future she wanted for her child. When Lara Renee was born in February 1985, the new parents were at the hospital. Renee and the couple, Mike Spry and Jean Rokos of nearby Interlochen, Mich., have met often since then, and they talk frequently on the phone. When Renee graduated from high school last spring, she invited Mike and Jean to come, and to bring Lara. She introduced them to all her friends as "the people who adopted my baby."

Renee and Jean and Mike, and certainly Lara, are engaging in what the child welfare system is beginning to call "open adoption," a form of child placement that allows and even encourages a far greater degree of communication among participants than ever was allowed in traditional adoption.

Some people, including social workers, automatically assume that "open adoption" is the same league as "open marriage," with a house full of mothers and fathers and a confused child. Indeed, one woman who recently had adopted via the closed method said she thought open adoption was "California-style adoption," with a very large family frolicking in a hot tub and conversing in the language of the self-actualization clinics.

That scenario may exist somewhere, but it's not representative of the trend that seems on its way to becoming the adoption of the near future. Despite the fears that many adopters cite when they first consider open adoption -- most often expressed in terms of a birthmother's arrival on the doorstep one, five or 20 years hence, demanding the return of her child -- openness seems to be gaining wide acceptance -- even among traditional agencies.

The quiet but steadily increasing acceptance of openness will be demonstrated here later this week when the Child Welfare League of America, which has served as the adoption system's arbiter for 65 years, holds its national conference in Washington. For decades the league and most of its member agencies have paid little attention to openness, urging confidentiality for everyone involved in the adoption process. But on Wednesday the league will present a discussion and workshop titled "Openness in Adoption: What Makes It Work?" Its task force on adoption is expected to come up with recommendations that may liberalize the group's position. David Liederman, the league's executive director, says, "It's likely that the recommendations will be the basis for our revising our standards." Openness, he said, has become "one of the very major issues" in adoption.

Dr. Sally Ryan Harrell, a Takoma Park psychologist who will speak at the league's meeting, knows openness works for her. Since she and her husband adopted their son 2 1/2 years ago through an agency in the West, they and the child's biological mother have corresponded and exchanged photographs. "Openness is not for everyone," said Harrell. "I'd just like to see the process recognized, and the option of openness made available to the people that are involved."

Up until now the only adoption agency in the Washington metropolitan area that advocates and routinely practices open adoption is the Fairfax County Department of Social Services. Carolyn Fowler, who heads the department's adoption unit, said the department revised its guidelines about two years ago and now recommends that prospective adoptive parents have some form of contact with the birthmother of a child they propose to adopt.

There is no official, accepted definition of open adoption. The term is an all-purpose name that's being applied to a number of variations on traditional closed placement. Significantly, openness seems to have developed without the official child welfare establishment. Indeed, it can be seen as a challenge to one of the traditional agency's most jealously guarded privileges: the power to serve as unquestioned middleman in a transaction involving human life.

Openness can mean something as uncomplicated as a birthmother's writing a letter and giving it to the agency, which then delivers it to the adopting parents, who are expected to turn it over to the child at the proper time. It can mean an exchange of photographs, either around the time of the birth or on an ongoing basis, but with no names, addresses, or phone numbers.

Or it can mean the active involvement of the biological parents in choosing their child's adoptive parents, with face-to-face meetings, an exchange of names, and perhaps an ongoing relationship.

OPEN ADOPTION is very open at Community, Family and Children Services of Traverse City, the Roman Catholic agency that supervised the placement of Renee's daughter. When prospective adopters sign up with CFCS, explained James Gritter, the child welfare and adoption supervisor, in addition to the usual interviews they are asked to provide a biographical sketch of themselves. An expectant mother reads through a number of these sketches and narrows the field of adoptive parents for her child; when she decides on a couple, a face-to-face meeting takes place. In some of the matches arranged by CFCS the parties enter into an actual agreement setting forth the ground rules for their continuing relationship. In others, the agreement is less formal. This is anything but "co-parenting," said Gritter. "Clearly the adoptive parents are doing the parenting, and the birthparent takes on the role of a special friend, and is an interested party in how the family grows."

The mother typically chooses the parents during the last weeks of her pregnancy; they often are on hand at the birth. The baby usually leaves the hospital with them, although the agency retains responsibility during the six weeks or so when the adopters are filing their legal documents. In Michigan, a final court order in adoption,, open or closed, usually comes after a year.

The procedure in Traverse City is about as open as adoption usually gets, at least outside those relatives-to-relative adoptions (believed to be the majority in the U.S.) in which everybody knows everybody else anyway. Whatever the degree of communication, open adoption is an idea that sounds more sensible the more you consider it.

Openness in adoption has evolved for a number of reasons, not the least of which is the public's recent inclination to take adoption, along with most other forbidden subjects, out of the closet. But it also reflects two other trends that are changing the face of adoption: a reaction against the closed, sealed-record adoption, and the recognition by practically everybody, including birthmothers, that they are human, too.

Closed adoption, the rule in the United States for many decades, has sought to impose on adopter and adoptee the fiction that once the transaction has taken place, the birthmother disappears into the vapor. Not too long ago, social workers were advising adopting couples to tell their children their biological parents were dead, in a usually futile attempt to remove them from the adoptee's mind. The problem with that is that many, maybe most, and possibly all adoptees, no matter how comfortable they may be with their adoptive parents, carry with them the questions, "Who is my biological mother?" and "Why did she give me away?" That the truthful answer probably would be undramatic, understandable, and easily accepted -- in most cases it's an out-of-wedlock pregnancy -- is not what's important; what's important is the question and the fact that the adoptee doesn't have the answer.

Searching for biological parents has become commonplace in the United States, and some states are even amending their laws to make it easier for reunions of adoptees and birthmothers to take place. There are many more adoptees, certainly, who do not undertake literal searches but who dwell on the unanswered questions. This need has become a potent argument against closed adoption.

Birthmothers are out of the closet, too. For a long time, the biological parents of adopted children didn't protest the role to which the system assigned them: castoff, stigmatized, forgotten, not only denied the right to know how their babies were turning out but also counseled (by certified social workers, no less, employed by the agencies that wanted their babies) to deny the whole process by which they had brought a child into the world. The result has been described by one of them as a "lifelong sense of psychological amputation."

Now that has changed drastically. Birthmothers, like most scorned and despised groups in society, have found strength in mutual support groups (Concerned United Birthparents, of Dover, N.H., is the best-known national organization), and they are making their voices heard. Because they are aware, as is everyone in the adoption system, of the current shortage of healthy, white infants available for adoption, they have learned that they control a valuable commodity.

Jim Gritter at Community, Family and Children Services is about as zealous about open adoption as it's possible to be. He explains the birthmothers' new awareness this way:

"There is a real shift in the supply-and-demand dimension to adoption. I always hesitate to put it in those terms, but it describes it so well. Whereas 30 years ago you had almost to persuade people to take a shot at adopting, now there are waves of them . . . Now the birthparents are beginning to discover that indeed they control a scarce resource. And if they really get awakened and aware and more militant about this, they can dictate how this process will happen."

THE AGENCIES favoring openness do not fit any particular pattern. Most seem to be voluntary or church-related institutions that took a look at openness, tried it and liked what they saw. Bobba Jean Moody of Spence-Chapin Services to Families and Children, one of the most traditional, respected agencies in New York, recalled recently that a year before, when she heard that another agency was encouraging birthmothers to write letters to adoptive parents, she was scandalized. "I thought this was some sort of bizarre aberration," she said. Now Moody encourages letters, too. Things move fast, she said, "when you start to look at the truth."

Omaha's Child Saving Institute, which is affiliated with the Christian Church (Disciples of Christ), has a three-level system of open adoption, with photographs and information at one end and face-to-face meetings on the other.

While there are risks in open adoption, just as in the closed version, agencies that practice it have reported, if anything, fewer problems than before. The risks of a birthmother's turning up on a doorstep (as might happen in a closed adoption as well) may actually be lowered, since the mother has chosen her child's new parents herself and has less reason to fear the outcome of the adoption.

"We're confident about this approach to adoption," said adoptive father Mike Spry in Interlochen, "and it's largely because we can see it's a solution to a lot of the problems that exist with traditional adoption." One potential problem in open adoption as practiced in Traverse City, he and Rokos said, is that in about 15 percent of the cases, the birthmother changes her mind between the time she has chosen the adoptive parents and the time the placement is made final. Often such a decision comes when the birthmother is in the hospital, after the baby has been born. This occurs in closed adoptions, too, but in those cases the potential adopters never know what almost happened; the agency doesn't inform them until the mother has completely relinquished her baby.

When a change of heart happens at CFCS, the adoptive couple waits for another child. The agency does a thorough job of preparing the couple for this possibility, and often when a birthmother shows signs of uncertainty the adopters find themselves encouraging her to keep the baby if that's what she wants to do. This happened with Mike and Jean on the day Renee left the hospital. Renee almost changed her mind. "I was not very nice to them that day," she recalled not long ago in an interview. "I was thinking of myself. I thought, 'I want her. She's not yours. You can't have her.' " Mike, remembering the same day, said he and Jean knew that "If Renee feels that keeping Lara is the best thing for her, we can only support her in that."

Outweighing the risk of a change in mind, said Mike, is the opportunity for the adopting couple to be a part of their child's life from the very beginning. "In a traditional adoption," he said, "you're probably not going to get that child until she's a couple months old. You'll miss out on a tremendous amount of bonding time. I can't imagine having missed out on the first eight weeks of Lara's life."

ALTHOUGH open adoption has no clear definition, and its proponents can't prove yet that it works, openness and its commitment to honesty erase instantly a lot of the myths and negative aspects of closed adoption. As for concern about birthmothers who show up uninvited on the doorstep, demanding their babies back, those who are involved say they aren't worried.

"I don't spend any time worrying about that," said Jean, as she held her child in her arms. "Maybe part of it is that we knew Renee before she released the baby. She knew us. We've maintained contact. And so, since we know her, I don't have that fear. She's comfortable with this. This is what she chose to do."

"She can come out here, and she can see that Lara is happy," added Mike.

Renee agrees. Last fall she was preparing to start a new life as a college student; she hopes to become a certified public accountant. She says other young women she knows who became pregnant and kept their babies have told her they were envious of her decision. A lot of people have asked her if she thinks she would ever want Lara back.

"Sure, I'd love to have my baby back," she said. "But I have to think of her. That's why I'm doing this. I'm really comfortable the way it is now. I don't think I'm going to go knock on a door and say 'I want my baby back.' I just can't do that. That would be really rude to Jean and Mike. They are really nice people. I couldn't have done better than them. I feel really good about what I did."