The federal government yesterday issued its official dietary guidelines, calling for Americans to eat less fat and more fruits, vegetables and grains.

In the central statement of federal nutrition policy, which is issued by the departments of Agriculture and Health and Human Services every five years, the government advised "moderation" in eating patterns, recommended the consumption of a wide variety of foods and urged Americans to be skeptical of the idea that "a food or supplement alone can cure or prevent disease."

"The guidelines we're releasing today reflect our expanding knowledge, and they respond to our citizens' demands for better, more usable advice about food and health," said HHS Secretary Louis W. Sullivan. "These new guidelines are clearer and more specific than ever before. They include more positive advice oriented to the total diet, with clear wording and specific numbers."

But the report was criticized by some nutritionists as omitting key dietary advice and playing down the importance to good health of eating sensibly.

"This is a Band-Aid and the American diet needs surgery," said Jayne Hurley, a nutritionist at the Center for Science in the Public Interest. "The report is totally devoid of the urgency that the situation deserves. The American diet contributes to hundreds of thousands of deaths a year due to heart disease, stroke, cancer, and diabetes. The government's mealy-mouthed advice can hardly be expected to spur the major overhaul in eating habits that most Americans should make."

Among the key recommendations in the report:

Fat should comprise no more than 30 percent of the total calories consumed in a day, and no more than 10 percent of that should be saturated fat. The average American diet currently contains 36 percent fat.

Consumers should attempt to meet specific food group targets every day, such as three to five servings of vegetables and two to four servings of fruit.

American should strive, in addition to eating a healthy diet, to maintain a healthy weight for their age and body type.

In several areas, the guidelines diverged slightly from the recommendations of previous years. For example, while the 1985 rules recommended that Americans "avoid" fat, cholesterol and too much sugar and salt, the new rules rephrase that admonition, urging Americans to eat those substances in moderation.

"Positive motivations work better than negative motivations," Agriculture Secretary Clayton Yeutter explained.

Some critics, however, said that the guidelines should have been stricter and that important new data contained in a recent set of nutritional guidelines published by the National Academy of Sciences (NAS) had been played down or omitted.

The NAS, for example, said that the amount of saturated fat in the American diet should comprise no more than 7 or 8 percent of total calories, not 10 percent as the guidelines state.

The NAS also recommended specific daily limits on cholesterol and salt consumption -- which the federal guidelines do not -- and stated explictly that cancer risk is increased by fat and decreased by fiber, fruits and vegetables rich in vitamins A and C.