"I kept running up against the fact that the process of men becoming equal partners at home was harder than people expect it to be," she says. "I kept trying to figure out why. There are a lot of answers in the workplace and the culture, but I didn't expect to find so many answers in the family."

Some of these answers can be found in women's behavior. The quasi-mystical "robe of glory" that envelops motherhood, says Braun-Levine, is "one of the perks of the traditional female role -- and while it's a burden, it's also a very nice feeling."

George Washington University law professor Naomi Cahn tackles the same subject in an upcoming article in the Yale Journal of Law and Feminism, arguing that women have to give up "some of the power and control that they currently exercise within the family" if they are to gain parity in the workplace.

Braun-Levine, Cahn and Brott emphasize that maternal gatekeeping is usually not malicious. Rather, it has to do with still prevalent assumptions that women are naturally better suited to caring for young children, and that the mother-child bond is deeper and stronger than the father-child bond. For many women, says Brott, "if you're not the one to whom the child comes running when there's a problem, you're not a real woman."

In the 1994 book "Peer Marriage," a fascinating study of egalitarian and near-egalitarian couples, Pepper Schwartz, a sociologist at the University of Washington, reports that a number of the husbands and wives she interviewed came close to full equality, only to pull back once they had children -- and that for the most part, the resistance to fully shared child rearing came from mothers, not fathers.

These women had been all for co-parenting in theory; once they actually became parents, Schwartz notes, they succumbed to "the siren call of motherhood" and started hogging the baby. In some cases, it was the men who rebelled against being shut out and pressured the women to curb their possessiveness.

It's not that women don't want men to participate; it's just that, quite often, they want Dad to be the junior partner. In a 1985 survey, only one in four mothers strongly endorsed 50-50 parenting, while two out of three seemed "threatened" by the idea.

Things may have changed in 15 years; unfortunately, the survey has not been replicated. However, Schwartz believes that the basic pattern is still the same: "There is much more expectation of male involvement," she says, "but bottom line, women tend to think that's more of an area where they have some superiority and control, just not as total as it used to be."

These observations are confirmed by some true confessions of maternal chauvinists -- women who admit to feeling secretly thrilled when Dad shows his incompetence and slightly disappointed when he copes well in Mom's absence.

A few years ago, Redbook ran an article called "My Husband Is Too Good a Father" by Beth Levine. Levine's husband, a home-based freelance writer like her, was an active, nurturing father to their young son, which was exactly what she had always wanted. What she had not expected was to feel hurt every time the boy cried for Daddy, not Mommy.

"I'm ashamed, but I hate that I am not the center of my child's universe," she wrote. "When I am honest with myself, what I really want is for Bill to be an eager but charmingly inept father, a soldier to my general."

Some mothers wisely keep such feelings to themselves. At worst, they may occasionally sulk when the child displays too marked a preference for Dad. But in some instances, maternal jealousy can turn ugly and wreak havoc on parents' and children's lives.

In the 1999 book "Divorced Dads," University of Arizona psychologist Sanford Braver describes the case of a woman who felt so upset and threatened by her husband's apparently closer bond with their young son (due both to the father's more flexible schedule and to his desire to be a "New Dad") that she filed for divorce and successfully fought for sole custody. Her husband, who was devastated by these events, felt that "she wanted a court of law to certify that she was indeed the better parent." The result was that instead of being in the care of his father while the mother worked, the boy was now left in day care.

Order "Mothers Who Think: Tales of Real-Life Parenthood" from the editors of Mothers Who Think.