Growing numbers of working mothers and their families may be suffering from malnutrition -- eating too much fat, salt and sugar and getting too little calcium, iron, thiamine, and vitamins A and C, nutritional experts report.

The typical family with a working mother now consumes about one fourth of its daily calories -- and some families as much as one half or more -- outside the home, much of that in the form of fast food. When these families do eat at home, dinners often are inexpensive frozen dishes that are low in nutritional value.

Such diet habits, nutrition authorities say, are a major health problem in America.

"We are seeing growing evidence that the working mother, and her family, may be suffering from malnutrition, not in the sense of the starving millions of Ethiopia, but in ways that still can be enormously harmful to their health," said Dr. Neil Solomon, former professor of medicine at Johns Hopkins and now in private practice in Baltimore, where he specializes in nutrition.

Solomon said the eating habits of American families in general are "in disarray" -- that people eat poor diets for a variety of reasons. But he said nutritional standards can fall even lower when both parents work outside the home.

"Sadly, the father too often feels the family's meals are the responsibility of his wife, and the wife, now holding two full-time jobs, feels she doesn't have the time," he said. "Caring for a family at the same time you're holding a 9-to-5 job takes the energy of a boisterous 5-year-old and the organizational skills of Gen. Eisenhower as he planned the Normandy invasion."

Virginia Beal, professor of nutrition at the University of Massachusetts, agrees.

"We're seeing a trend that is cause for great alarm," she said. "The number of daily calories consumed outside the home by the families of working women is increasing, and when they do dine at home, more and more of them are resorting to the less expensive -- and less nutritious -- frozen meals sold in supermarkets.

"Working women are in the market for ways to shave just a little time from their schedules, and they may be choosing the wrong ways from a nutritional standpoint."

At Cornell University, researchers Karen Bunch and Lana Hall analyzed food consumption patterns compiled by the U.S. Department of Agriculture. One of the things they found was that the amount of food eaten outside the home increased with the number of hours mothers worked away from home.

On the average, the families of women with full-time jobs consumed 28 percent of their daily calories outside the home, much of that in the form of fast food. And while some nutritionally minded families may consume less, others may be eating as much as 57 percent of their food away from home.

Bunch and Hall found that in families in which mothers did not hold outside jobs, average calorie consumption outside the home was 12 percent.

When the mother worked one to 15 hours outside the home, outside consumption climbed to 15 percent, and at 16 to 30 hours of job-related activities for the mother, it averaged 21 percent.

The next significant jump in food consumption outside the home came among the families of women with jobs requiring 40 hours a week or more. Their families, on average, consumed 28 percent of their calories away from home.

The actual figures may be substantially higher for all groups, the researchers warned, pointing to their suspicion that many of those surveyed underreported the amounts of foods they consumed away from home.

The diet away from home, Bunch and Hall said, too often is lacking in calcium, iron, thiamine, vitamins A and C, riboflavin and fiber. What it does have, however, is an abundance of fats and salt.

In fact, the researchers examined the nutrient content of typical fast-food meals offered by a number of major chains and said they ranged from a low of 900 calories for two pieces of fish, french fries and a cola in one restaurant to a high of 1,300 calories for a burger, shake and french fries at several others. Most of those calories were in the form of fat.

"If the consumption of fast foods away from home continues at the current rate, nutrition-related health problems may increase," they said.

The federal Bureau of Labor Statistics reports that of mothers with children aged between 6 and 17 years, 65.4 percent of those who are married and 84.1 percent of those who are divorced now work outside the home.

Nutritional experts say several factors contribute to the eating patterns in the working mothers' households:

* Time. Most working mothers actually have two full-time jobs, one in the home, one outside it. With little time for planning meals, careful shopping, preparation and cleanup, they turn to whatever is fastest, which often means eating out.

* "The hassle factor," which Ardyth Gillespie of Cornell University describes as the woman's attempt to provide whatever will please all the members of the family most, since meals often are the only times the families of working women have together. And what will please the kids in the family might not always be the most nutritious foods.

* A lack of basic nutritional know-how. Millions of Americans never have been taught the basics of good nutrition, knowledge that would allow cooks to choose nutritious shortcuts while feeding their families.

Contributing to the problem is the fact that growing numbers of children, particularly teen-agers, eat fast foods whenever they can -- including skipping out on a balanced school lunch so they can visit the nearest hamburger house.

In fact, the Bunch-Hall study at Cornell revealed many teen-agers interviewed by USDA food consumption experts may actually have underreported the amount of junk food they eat.

Solomon said a diet like that outlined by the Cornell researchers could lead to weight problems and increase the risk of heart disease, diabetes and high blood pressure. Lower calcium consumption increases the risk for women of osteoporosis, a condition that leaves bones fragile and fracture-prone later in life.

Recent research at Cornell Medical College and the Oregon Health Sciences University strongly suggests a relationship between calcium deficiencies and the onset of hypertension, he said. Iron deficiencies can cause serious anemia, and fiber intake is thought to help prevent some forms of cancer. Inadequate thiamine and other B vitamins can cause a variety of health problems, including irritability and depression.

"I could go on and on," Solomon said, "But to sum it up: The weaknesses in the diets of working women and their families are a textbook case of malnutrition."