Not long ago, a group of top corporate executives attending a seminar at Harvard were asked about the family patterns of their employes. Many of them guessed that male breadwinners, with wives at home, made up one-half to three-quarters of the people working at their companies.

Dead wrong. Those executives have their heads in the sand.

Nationwide, only one employe out of 10 conforms to that old-fashioned pattern, according to The Conference Board, a business research group. The rest are working couples or single people.

That executive ignorance helps explain why most employe benefit plans are still designed with traditional families in mind. Too many fuddy-duddies remain at the helm of large companies, and for them, footloose single people, working mothers and divorced fathers are a shame or a nuisance.

The personal needs of these nontraditional employes may seem like a kamikaze attack on company policies. They want flexibility, independence, choice -- and to the rigid manager, that means flouting the hallowed corporate order. Yet the disparate needs of nontraditional workers are rapidly becoming the norm, and some enlightened companies are shaping their employment practices to meet these new requirements.

The innovators do it not for love, but for money. By accommodating the diverse lifestyles of their employes, they attract and keep good workers, lift company morale and wring more efficiency out of every dollar spent on benefits.

A recent Conference Board survey of new-style employe-benefit plans found that the companies sponsoring them have many things in common.

They tend to be in high-tech or scientific industries, or in businesses that serve the consumer market. They have a relatively young work force or a high proportion of female employes. They have more women in management positions, which helps explain their sensitivity to changing family patterns. They're nonunion companies, or are located in "progressive" communities, or remain close to the paternalistic tradition of the founder.

Their ranks include Honeywell, IBM, Levi Strauss, Zale Corp., Tandy Corp., Borg-Warner, American Can, Dana Corp., Transamerica, Occidental Life Insurance, Control Data and Hewlett-Packard. Among their practices:

*Flexible work schedules. The easiest change is to switch to "summer hours" -- allowing workers to quit work at Friday noon in the summer months. Employes get more free time, and families get more time together when children are home from school.

From there, many companies go on to staggered work schedules, allowing workers -- within limits -- to pick their starting and quitting times.

A smaller number of companies have experimented with job sharing (where two employes, usually women, share a single job), work-at-home arrangements and three- or four-day workweeks, in which employes work 10 to 12 hours a day. (Many women don't like shorter workweeks, The Conference Board reports, because they wind up doing an extra day of housework.)

*Time away from work. More companies are making it possible to take flexible vacations in the form of long weekends or half-days. Unused sick leave may be lumped into a vacation, and there are more "floating" holidays that employes can use at will. At some companies, unused days off may be traded for cash.

Most companies have not yet confronted the issue of days off to care for a sick child or spouse. One exception is Atlantic Richfield, which gives up to six paid days a year for tending the sickbed of a family member.

A few companies allow leaves for fathers as well as mothers after childbirth, but only a few men take them up on it.

*Flexible employe benefits. "Cafeteria" plans are proliferating. These typically offer employes a basic benefits package of life and health insurance, sick leave and vacation, then let them "spend" a specified number of credits for the additional benefits that will suit them the most. Working parents usually choose family medical coverage and more life insurance. Single workers without children often choose more disability coverage and a higher contribution to a thrift plan.

*Child-care assistance. More companies are edging into child care -- usually not with their own day-care center, but with technical and financial assistance to community centers that employes use.

All these programs are in their infancy. When the corporate fuddy-duddies finally retire, and today's younger generation moves up the ladder, you can expect American business to be dragged wholesale into far more sensible personnel practices than are common today.