"Usually, this strange look comes over people when I tell them I have a 13-year-old son, but that he lives with his father.

"They never ask, 'Why?' but I feel compelled to explain and end up automatically defending myself because I still worry that people are thinking bad things of me.

"There's still the old social stigma. When I told my own mother she said, 'You are a mother , how can you give up your own child?"

Jackie Brunell, whose son Paul lives with his father in the D.C. Palisades while she begins a new life in California, is one of a small but increasing number of divorced women challenging society's traditional values and leaving the day-to-day nurturing to their former husbands.

Brunell's decision -- like that of many mothers who take this controversial route -- did not come easily, nor suddenly.

Only after trying several different living arrangements for their son since they separated amicably in 1972 (when he was 3), did the Burnells decide that at this stage of his life, it would be best for Paul to remain with his father on the East Coast.

"We had a strong, shared commitment to parenthood that was bigger than our differences," says Jackie Brunell, who met her former husband while both were working on Capitol Hill. She returned to school to study nursing (she had been an executive secretary), juggling day care and the constantly changing shifts of a floor nurse. She is now in nursing research, which brings her to Washington frequently.

Still, the old labels -- like "runaway mother" who has "abandoned her children" -- are apt to haunt noncustodial mothers like Jackie Brunell.

Their children's happiness, financial worries, father's rights, time to rebuild careers or finish school are major factors for these untraditional parents daring to confront the taboo. (Good mothers do not leave their children).

"Gee, I wish I had the guts to do what you did," is the echo these mothers say they hear privately from other mothers, divorced or staying in a bad marriage because they are convinced they can't handle their children and earn enough money at the same time. (For every dollar that men earn in fulltime positions, women earn 60 cents for similar work, according to recent Labor Department figures. And only about half of mothers with custody who are supposed to receive full child support get the full amount).

But publicly, volunteer noncustodial mothers report feeling like modern-day martyrs, in the forefront of what may be a revolution in the custody and co-parenting of children.

Whether it's a temporary arrangement in which the mother still shares custody and major decisions while she regears herself for her new role as a single; or whether it is reverse custody in which the father takes over during the teens; or whether it's total separation of mother and child, the mothers feel they are treated the same. "As if you're incompetent," as one put it, "an alcoholic, prostitute, or in a mental institution, just like it used to be, the only reasons that a woman didn't have her child."

"The most difficult thing I ever did in my life was to drive away, by myself, to begin that cross-country trip back to California," says Brunell, 44. "David and Paul -- who was trying to be a little man -- were standing there with their arms around each other, fighting back the tears. I cried that whole first day and kept asking myself, 'Why am I doing this'"?

Three years later, her former husband wrote her a 14-page letter thanking her for "remarkable unselfishness".

Today, says management consultant David Brunell, 44, "I really worked at changing my own life around, too. It takes two to make this work." Both Brunells came from divorced families, and wanted "to minimize the effects of our divorce on our son as much as possible."

"More and more of these women are coming out of the closet and others come to us to consider sharing or giving custody to their children's father," says Thomas M. Smith of Parents Without Partners (PWP) International. The organization is headquartered in Washington, with 195,000 members in the U.S. and Canada.

"They are saying, 'Hey, world, I am a mother without custody and I don't want to be treated like an animal. Just because I gave up custody doesn't mean I'm not a good human being'".

Even the Census Bureau, says Smith, does not count noncustodial mothers or fathers as "parents" in their yearly count. "It's all part of the closet mentality." The Census also does not reflect what in professional circles is seen as a marked increase in the number of fathers with shared or sole custody.

"Mothers without custody aren't any worse than all the noncustodial fathers," says 33-year-old Jan Koehler of Woodbridge. She gave up custody two summers ago when her marriage broke up and she decided she and her now 6-year-old daughter Joy "just couldn't live on what I was making.

"I was in ill health with a serious kidney condition, and the dissolution of my marriage shattered me. Plus, her father adores her and is a very good parent.

"People have choices today and women aren't the only choice as custodial parent," maintains Koehler, one of the noncustodial mothers interviewed on "The Phil Donahue Show" aired yesterday in Washington. "But it's still a haunting place to be".

A consulting firm associate, Koehler hopes to network with similar mothers here and nationally and is creating workshops for Washington-area professionals in non-traditional families.

Since her husband made a job change to Philadelphia, Koehler sees her daughter only on school holidays.

Although they may be intellectually sure of their decision (sometimes even made congenially with their former husbands) noncustodial mothers are still not without guilt at times. They worry that their children will misunderstand, feel abandoned, be turned against them someday. And they must deal with the pain of being physically separated from their children, who may be thousands of miles away.

"It's a societal 'no-no' not imposed on men. The kind of ingrown conviction that it's okay for Dad to leave, but not okay for the mother," says a Montgomery County family therapist whose clients include women who have given up custody. "These mothers wrestle with the guilt of not fulfulling the proper roll of the female".

"Especially in this Moral Majority atmosphere, it's a very sexist issue . . . extremely emotionally deep," adds Vienna social worker Tobey Milne, who finds noncustodial mothers banding together in small therapy groups to counteract isolation and castigation.

"It was the most painful thing I've ever done in my life, but in the last 5 years, I've had 20 years of growth I wouldn't have been able to achieve otherwise," says 42-year-old Jackie Miller, teen-age son and daughter, who have spent some of their high school years with their father in Michigan.

"I felt like a bad person so I overachieved myself silly, got all A's, wrote great papers, and invested in real estate," says a 39-year-old Bethesda woman, now remarried and a fulltime graduate student, who gave up custody of her children when they were 8 and 12. She, like several others interviewed, didn't want their names used. (Repeatedly, custodial fathers also wanted to protect their former wives from "additional pain," because as one put it, "she suffered so much").

"Often," says the Bethesda mother, "I got jealousy from my friends who said I was so lucky to have time to myself, not to be saddled with all the kids. But there are trade-offs.

"They'll be there when their daughter gets her first driver's license and they can help her pick out her prom dress and watch their son win gold medals."

The Bethesda woman, whose two children are now teen-agers, says she only wishes that back in 1976 joint custody would have been possible in Montgomery County.

"Last Christmas I had to send them checks because I didn't even know my children's sizes and I don't even know who their teachers are. I think my former husband and his new wife have intimated to the private school that I died.

"Men have formed Fathers United (an organization to promote fathers' rights), but women have felt so alone. They have felt so much more guilt and shame as noncustodial parents.

"Still, I think I did the right thing, leaving the children in the only neighborhood and schools that they had ever known. I could not afford to stay there, and my ex-husband would not give me any support money."

McLean real estate agent Ellie Clark, 45, says the hardest moments were when her little boy, now 9 but only 4 when she left, made something at school for Mother's Day and gave it to the housekeeper.

Despite that kind of pain, Clark, who still has joint custody officially (even though her four children, age 9 to 21, now live with their father in California), says the arrangement has worked out "best for all."

"I remember my own divorced mother saying, 'I wish I would have had that option.'"

A Maryland research assistant who once helped put her husband through school -- and after their divorce was ordered by the courts to pay child support -- says she can't afford for herself the designer jeans, $15 haircuts and fancy vacations her three teenagers have living with their remarried dad. She's also had some other second thoughts about the arrangement.

"Now I wouldn't make the same decision, but I needed a period of growth for myself. The kids are doing well in school, and sometimes in the future I would like to change custody.

"You just don't realize how important the little things are, like being there to take them to the dentist, going out shopping or having lunch together. That's where life and love is, just dressing up for Halloween together."

Warns a 40-year-old Washington mother of two teen-agers, who is now remarried: "I did it for the kids, and it worked against me. Now the women my ex-husband is living with goes to the parent-teacher conferences and the school conferences. The school counselor won't even talk with me about my own daughter because I don't have custody."

"Some of these same things fathers without custody have been giving up for years," notes Cora Lynn Goldsborough, a McLean psychologist and a frequent witness in child-custody cases. Goldsborough believes mediation or conciliation courts are one answer to today's expensive and painful custody battles.

"The increase in the father's rights movement doesn't have to hurt the women," adds PWP's Smith. "Some balance needs to be struck, and maybe joint custody is the answer in more cases."

Former Boston radio talk show host Ellen Kimball -- who last summer sent her then 11- and 12-year-olds off to live with their father on a rural Vermont farm because of its smaller and more disciplined schools -- thinks "serial custody" is the solution. (Parents may take turns with custody, according to different stages in a child's life.)

"It's like the Kramerization of the country, a new humanistic wave," claims Kimball, who formed the organization, "Mothers Without Custody," a non-profit support group in Massachusetts which she hopes will grow nationally.

"I had custody for many years, and the children were missing the opportunity to know their father in a real way. Everybody deserves a right to live with their child, and the children need to know that 50 percent of their genealogy."