Women who are fat below the waist, primarily around the hips, have the most trouble dieting, through no fault of their own.

Women who are fat primarily in the upper body are the most successful dieters. And they should diet, because they have a high risk of diabetes.

These findings were announced yesterday by the Medical College of Wisconsin.

Dr. Ahmed Kissebah surveyed 15,000 women throughout the United States and Canada and made a detailed study of 52 women at Milwaukee County Hospital's General Clinical Research Center, a research ward supported by the National Institutes of Health.

The studies showed how, and apparently why, some women lose weight more easily than others.

Also, Kissebah said, "these studies show there is a large group of women, the upper-body obese, who should be watched for diabetes, and given every help possible so they can diet. This can lower the risk of diabetes, also of high blood pressure and heart disease."

The first hint of a link between diabetes and the location of body fat came from Dr. Jean Vague in the 1970s. He noted that diabetes seemed to occur more often among obese women whose fat was concentrated in the upper body.

Kissebah surveyed 15,000 obese women enrolled in TOPS (Take Off Pounds Sensibly) clubs. He found the same pattern.

"About 25 per cent were upper-body obese," with excess weight around the waist, bust, neck and arms; "about 25 per cent, lower-body obese," with excess weight around hips, buttocks and thighs, he reported. "Fifty per cent fell in between, though tending about half and half to be more one way than the other."

He and colleagues then studied 25 upper-body obese and 18 lower-body obese women--many in both groups from 20 to 30 pounds overweight--and nine women of normal weight. The women with upper-body obesity tended to have high levels of insulin, glucose and fatty acids, levels which often precede diabetes symptoms.

The women with lower-body obesity had no such signs but they often have other problems, especially joint degeneration and arthritis.

When dieting, the upper-body obese readily lost body fat, apparently, says Kissebah, because they have larger-than-normal fat cells which could be reduced in size by dieting.

The lower-body obese tended to lose fluid and muscle tissue and some fat from large fat cells in their upper body. But the fat cells in their lower body, which are normal-sized but closely packed, remained largely intact.

"It's much easier to shrink a fat cell than kill it," Kissebah explained.

"It's very frustrating for these lower-body obese women," he added. "They may diet for months, only to look, from the waist down, as though the diet never started."

Persistent dieting may even harm them, he added, since they may lose muscle tissue, including heart muscle, while keeping their stubborn fat. Or they may become so frustrated that they abandon all dieting.

Overweight men, like upper-body obese women, tend to have extra-large rather than closely packed normal fat cells, although men tend to concentrate their weight around their middles for the typical "pot belly."

Male hormones seem to be part of the picture for both men and women. Both sexes normally have both male and female hormones. But women who are upper-body obese have more male hormones than women with heavy bottoms, while the heavy-bottomed women have more female hormones than would be expected.

"Strong hormonal influences," perhaps genetic in origin, seem to be at work, Kissebah believes.