Martha Duffley leans over her son's crib, stretching the silent moment.

Too soon, it's the 6 a.m. feeding, the scrambling to get the 5-month-old dressed and packed for day care. In no time, it's the first goodbye."No tears," the new mother promises herself, swinging her compact car away from suburbia and into the commuter traffic surging toward downtown Boston. "No time for tears."

It's Martha's first day back.

She is just one of about 1.9 million women who return to jobs each year after having a child. Some mothers prefer to work; others have no choice.

Regardless of financial circumstances, fewer than 10 percent of Americans live in what once was the traditional family headed by a male breadwinner. Sixteen percent of women with infants worked in the early 1960s, compared with more than 50 percent today.

"Women are still asking themselves: `Am I doing the right thing?' " said Barbara Reisman, executive director of the national Child Care Action Campaign. "Our mothers led a different life, and theirs is the only model we have."

But that nuclear, 1950s model is, for many mothers, far out of date. The rules have changed, the days grown longer and more complicated.

-Martha, a Boston postal supervisor, fears her son's caregiver seems more a mother to him than she does.

-Pam Salazar, a television reporter in Dayton, Ohio, wonders whether continuing to breast-feed after returning to work seems unprofessional.

-Vicki Sugarman, who shares a job managing promotions for a company based in Stoughton, Mass., frets over finding convenient and reputable day care.

-Her partner, Janet Aikens, worries that their job-sharing experiment at Reebok International Ltd. may be tokenism rather than the start of a common option for working mothers.

-Sheila Michelli, an Army captain in Fort Lee, Va., struggles to negotiate shared parenting responsibilities with her semiworkaholic husband.

-Cynthia Sartin, a nurse in downtown New Orleans, feels guilt's stab each time she tucks her sad-eyed baby girl into bed and slips out the door.

-Amanda Wallis, a San Francisco bank executive, realizes time for herself has disappeared amid the crazy scramble that is modern motherhood.

These and millions of other moms are exhausted. Yet despite their daily race, "having it all" still too often means living with the uncomfortable sense that everything is only half-done.

No simple "how to" manual exists to ease the dueling pressures or explain away irrational guilt. Working parents still are experimenting and making errors.

"If I were giving the nation a report card, I would have to give us a `C,' " said Joseph Pleck, a family issues researcher at Wheaton College in Norton, Mass. "You can expect a little more help from your husband, but don't expect much from your employer."

One in five men now pitches in at home, and, Pleck said, their increased participation in flexible hours, paternity leave and other child-care progams has helped debunk employers' perception that these are special women's benefits.