A LESSER LIFE: The Myth of Women's Liberation in America. By Sylvia Ann Hewlett. Morrow. 461 pp. $17.95.

SING HOSANNAS! Someone reputable has finally said it in print: Very few middle-class American women can pursue fast-track careers while also fulfilling the responsibilities of motherhood. This is not, as some would have it, because females lack the brains, drive or aggressiveness to reach the top in competitive fields; or because they have an innate compulsion to spend the daylight hours wiping small noses and sewing Halloween costumes; or indeed, because children need the constant company of a biological parent.

It is rather, as Hewlett persuasively argues, because American society simply lacks the institutional supports necessary to allow an ordinary mortal to do more than one full-ime job in a single 24-hour day. Where those supports do exist, namely, in nearly every other industrial democracy, mothers do vastly better in the work force while producing millions fewer latchkey children than in this supposed land of enlightenment and progress.

Hewlett discovered the dirty secret of women's liberation the hard way. A series of obstetrical catastrophes forced the choice between achieving tenure at Barnard College and bearing healthy babies. While Hewlett struggled through difficult pregnancies and futile stabs at breastfeeding between classes and committee meetings, her sister Helen, teaching in their native Britain, enjoyed nearly half a year of mostly paid maternity leave and the right to her job back with no loss of seniority; Hewlett was certain this constituted a special deal. But no, Helen had simply availed herself of a British worker's normal rights -- which are actually rather stingy by European standards.

While other countries pay family allowances, provide subsidized child care, encourage flextime, allow absences for children's illnesses, and guarantee a mother's right to her old job even if she stays away for years, distinguished American women's colleges keep the tenure clock running while faculty members recuperate from complicated Caesareans, famous American hospitals permit pregnant and nursing medical residents to work themselves to the edge of exhaustion, ordinary American employers treat child rearing as an irresponsible idiosyncracy.

And beyond the often insurmountable dilemmas of American women like Hewlett, who has a prosperous husband, and beyond even the added problems of the majority of wives who must help pay for the necessities, there yawns the appalling travail of the single mother. Divorce reform in nearly every state has lately stripped wives of most of the financial protection marriage used to afford. Courts now order only a minority of ex-husbands to pay even minimal child support, and only a minority of those actually pay anything at all. Divorced mothers, therefore, must generally raise children alone on the inadequate incomes that most women's jobs provide -- incomes far too small for the exorbitant cost of decent child care in this country. So the richest nation on earth, all the while congratulating itself on its interest in its children, condemns millions of them to penury or long, lonely hours alone with the TV.

WHAT HAS caused the disgraceful -- and worsening -- situation that Hewlett compellingly describes and documents? She accuses two main villains, the motherhood cult of the 1950s, which enshrined suburban child rearing as the highest womanly art, and the American version of feminism, which campaigns for equal rights and against the special supports and protections that help even a mother's chances in a male-oriented job market. I wish she had looked deeper than generalizations about the popular cultures of the 1950s and the 1970s. As she herself points out, Elizeth Cady Stanton and Eleanor Roosevelt argued generations ago that mothers needed special social consideration more than they needed formally equal rights.

Where we differ from the Europeans seems to lie deep in our attitudes toward ourselves as individuals, as parents, as workers and as citizens. We see the decision to bear children as a purely private concern; they see it as a service to the community, rather analogous to military duty. Far from losing their jobs -- a common fate of the American mothers -- Italian women receive two years of additional job seniority for every child they bear their grateful nation. Hewlett fleetingly alludes to the characteristic mentality that grew out of Europeans' experience with an entrenched class system, but she fails to follow up this promising lead.

At the main task she sets herself, though, she succeeds very well indeed. The picture she draws of American mothers in 1986 is stark, scary, and utterlyconvincing. Every American who is one, or has one, or has been married to one, or ever hopes to be one needs to think deeply about the questions Hewlett raises.