For years the federal government has refused to take a stand on what specifically constitutes a nutritionally sound diet.

The Department of Agriculture, from which such information would ordinarly flow, is concerned that food processors, sugar growers and the cattlemen might be angry if it suggested that some foods are not nutritious at all or should be eaten sparingly. So they put out publications, printed at taxpayers' expense, they say: "All food is good food."

Finally, last week, another governmental body, obviously not concerned about what the food industry might think, issued a report that makes specific recommendations on how Americans must drastically change their eating habits if they want to live longer.

It will come as no surprise to most Americans that what they eat may be killing them. This has been the theme of many recent scientific and lay publications, of numerous scientific conferences around the country and a considerable number of congressional hearings.

But the report released by the Senate Select Committee on Nutrition and Human Needs, titled "Dietary Goals for the United States," is likely to become the linchpin for all these nutritional recommendations, just because it has the stamp of approval of a government body.

The framers of the report are telling people to cut out soft drinks and cut down on red meat, accusing television commercials and fast-food restaurants of contributing to this country's poor dietary habits. They recognized their position will be controversial. This is because, in part, they are basing their recommendations on findings of probable association between dietary habits and incidence of disease. But they said: "The public is confused about what to eat to maximize health" and it is the government's obligation "to provide practical guides to the individual consumer as well as set national dietary goals for the country as a whole."

Dr. Mark Hegsted, professor of nutrition at Harvard University and one of the three nutritionists who helped write the report, said: "There will undoubtedly be many people who will say we have not proven our point; we have not demonstrated that the dietary modifications we recommend will yield the dividends expected.

"The question to be asked therefore, is not why should we change our diet, but why not. "What are the risks associated with eating less meat, less fat, less saturated fat, less cholesterol, less sugar, less salt and more fruits, vegetables, unsaturated fat - and cereal products - especially whole-grain cereals? There are none that can be identified and important benefits can be expected."

When the report was announced, the chairman of the Nutrition Committee, Sen. George McGovern (D-S.D.), noted that "American diets have changed radically within the last 50 years with great and often harmful effects on our health.

"Since the beginning of the 20th century the composition of the average American diet has changed radically. Complex carbohydrates - fruits, vegetables and grains - which were the mainstay of the diet, now play a minority role. At the same time, fat and sugar consumption have risen to the point where these two dietary elements alone now comprise at least 60 per cent of the total caloric intake, an increase of 20 per cent since the eaarly 1900s."

There is epidemiological evidence that these dietary changes are related to "six of the 10 leading causes of death: heart disease, cancer, vascular disease, diabetes, arrterioaclerosis and cirrhosis of the liver."

According to another Nutrition Committee study, improved diet could reduce heart and vascular disease by 25 per cent; infant mortality by 50 per cent; obesity by 80 per cent; cancer incidence and death by 20 per cent. In addition, 50 per cent of the cases of diabetes might improve or be avoided.

The committee recommendations, however, would means drastic changes in eating habits for most Americans:

An increase in consumption of complex carbohydrates so that they account for 55 to 60 per cent of the caloric intake.

Reduction in sugar consumption by 40 per cent so that it accounts for about 15 per cent of total caloric intake.

Reduction in overall fat consumption by 10 per cent so that it accounts for about 30 per cent of total calories and a shift from saturated fat to polyunsaturated and mono-saturated fat by 10 per cent.

Reduction in salt consumption by 50 to 85 per cent.

To achieve these goals, specific guidelines are offered on how to change food selection and preparation:

An increase in the consumption of fruits and vegetables, particularly those that are fresh and least processed, and of whole grains, will raise the consumption level of complex carbohydrates. The report says that diets high in these carbohydrates may reduce the risk of heart attack, are important in the treatment of diabetes and may help to increase the consumption of fiber as well as micro-nutrients, vitamins and minerals. In addition it says eating more fruits, vegetables and whole grains "is likely to ease the problem of weight control" because the high water content and bulk of fruits, vegetables and whole grains "can bring satisfaction of appetite more quickly than do foods high in sugar and fat."

To increase whole-grain intake there should be increased consumption of whole-grain bread and of hot cooked cereals because they are less refined and less processed.

"In ready-to-eat cereals, sugar-coated cereals should be avoided," the report says, as should granolas because they are high in calories and fat.

Consumption of foods high in fat, particularly those high in saturated fat, and foods high in cholesterol should be reduced. The report says that eating less fat will help control obesity, heart disease and certain forms of cancer.

Dr. Gio Gori, deputy director of the National Cancer Institute, told the Senate Nutrition Committee last July that "there is . . . a strong correlation between dietary fat intake and incidence of breast cancer and colon cancer. As the dietary fat intake increases, you have an almost linear increase in the incidence of breast and colon cancer."

A reduction in overall fat and saturated fat consumption can be achieved by eating less red meat and more fish and chicken; using skim milk instead of whole milk; eating more peas, beans and lentils, uncreamed cottage cheese and other skim milk cheese products. The report recommends eating foods where the percentage of calories from fat is under 30 per cent. Other such foods include: lean beef; shellfish and fish such as bass, oysters and [WORD ILLEGIBLE] salmon; chicken without the skin; porridge and most breakfast cereals except granolas; bread.

Specifically, to decrease saturated fat consumption, vegetable oils, with the exception of palm and coconut oils, should be used instead of animal fats such as lard and butter.

Since the recommended daily consumption of cholesterol is 300 milligrams (mg), eggs must be used sparingly. One egg yolk contains 250 mg of cholesterol. Other foods high in cholesterol include brains, kidneys, liver and heart.

To reduce consumption of sugar, implicated in tooth decay, possibly diabetes and an increased need for certain vitamins, one of the best places to start, the report says, is with soft drinks. "Total elimination of soft drinks from the diet, for many people, would bring at least half of the recommended reduction in sugar consumption." The second major area for cutting sugar consumption is baked goods.

The report says that the amount of salt most people need could be supplied without adding salt to food. Salt has been found to cause an increase in blood pressure and hypertension. According to one study, "20 per cent of the United States population is susceptible to hypertension and up to 40 per cent of older people."

In addition to leaving the salt shaker on the table, the report suggests leaving the potato chips and pretzels in the store. Other foods that are naturally high in sodium (salt) or that have a lot of added salt are: bacon, bologna, corned beef, ham, luncheon meats, sausage, salt pork; anchovies, sardines, caviar, dried cod and herring; processed cheese and cheese spreads, roquefort, camembert and other strong cheeses; vegetables packed in brine such as pickies and sauerkraut; popcorn, salted nuts, olives, commercial bouillon, catsup, seasoned salts, chili sauce, meat extracts, sauces and tenderizers, prepared mustard, relishes and cooking wine.

By following these recommended dietary goals, the committee contends, not only is there likely to be an increase in the life span and a decrease in illness, but there can be a "significant reduction in food costs. Savings can be achieved through home preparation and through reduction of and substitution of fats, sugar and expensive, fatty protein sources."

"The most dramatic savings made by a reduction of sugar consumption," the report says, "result from cutting back on or eliminating purchases of candy, sweet baked goods and soft drinks."

How did Americans ever develop such unhealthy eating habits? According to Hegsted, "it is happenstance related to our affluence, the productivity of our farmers and the activities of our food industry.

"The diet we eat today," he said, "was not planned or developed for a particular purpose."

But one of the factors affecting it is television food advertising. The report notes that most of what is advertised on television is "junk food," that is food with no nutritional value, and it has a tremendous impact on what Americans eat.

A study quoted in the report says: "Television is the primary source of information for the American public today. On the other hand, positive nutrition education from other sources is comparatively minuscule in the country. Thus it is reasonable to infer further that these combined circumstances are significant contributors to the current array of nutrition-related health problems."

To bring some balance to this situation the report says Congress should provide money for nutrition education programs to include: extensive use of television to educate the public in the potential benefits of following certain dietary goals; nutrition education in the classrooms and school cafeterias including nutrition education for the people who prepare and serve school breakfasts and lunches; nutrition education in federally funded food programs such as food stamps; nutrition education conducted by the extension service of USDA.

The report also recommends mandatory food labeling to include the following information: per cent and type of fats; percent of sugar, milligrams of cholesterol and salt; caloric content; complete listing of food additives; nutrition labeling which is currently voluntary.

When McGovern introduced the report last week, he said he hoped it would be "useful to millions of Americans. In addition to providing simple and meaningful guidance in matters of diet, it should also encourage all those involved with growing, preparing and processing food to give new consideration to the impact of their decisions on the nation's health. There needs to be less confusion about what to eat and how our diet effects us."

But McGovern would not even guess when there would be any observable impact from such dietary changes.

One of the nutritionists at the press conference, Dr. Philip Lee of the University of California, said "the important thing is the first step has been taken. It may take a generation, but it will have an immediate effect on some."

Copies of the report can be obtained by writing to: Senate Select Committee on Nutrition and Human Needs, 119 D St. NE, Washington, D.C. 20510.