When University of Maryland demographer Harriet B. Presser was doing a study of child-care practices she noticed something unusual:

"A very high percent of the women reported that the care of their preschool-age children was by the father, and the father also was employed full-time."

The women were in occupations such as waitressing, nursing, telephone operators--"occupations that clearly looked like shift work. All the reports came out just in regard to individuals, and not with regard to families. They had the marital status of the spouse but you didn't know anything about the spouse."

When she and co-author Virginia S. Cain researched the matter further, they discovered an "enormously high rate of shift work among couples." (In more than one-third of dual-career couples with children, at least one spouse works shift work.)

This situation, says Presser, "is not just a blue-collar phenomenon. It's clearly among professionals and entertainers, among others."

Among other findings of their study, "Shift Work Among Dual-Earner Couples With Children," which appeared in Science magazine:

* More than half the dual-earner couples have children.

* 10 percent of the couples have "no overlap whatsoever" in their work schedules.

* The husband is usually on an evening shift, the wife on a nonrotating day shift.

"A lot of the people," says Presser, "have this continuously changing schedule among one of the spouses. It really can be difficult."

Among possible benefits: "The children get more parent time, especially if they are preschoolers who are home all the time anyway."

However, the authors see these areas as important for further study: the quality of child care in shift-work households; the quality and stability of marriages among shift-work couples compared with others; the distinctive effect of shift work on the division of labor within the home and on marital power.

"The answers to these questions," they stress, "are increasingly important."