NO ONE COULD have guessed what the aftermath would be in January 1977 when Sen. George McGovern piled up 125 pounds of sugar, 100 pounds of lard and 300 cans of soda pop in a hearing room and announced the publication of Dietary Goals for the United States.

Ever since that day when McGovern's Select Committee on Nutrition and Human Needs told Americans that if they wanted to live longer and better they should cut back on fat, sugar, salt and cholesterol and eat more fruits, vegetables and whole grains, there has been an inexorable movement toward a national nutrition policy.

Even McGovern is surprised at how things have turned out. He told a nutrition conference yesterday that "we did not fully gauge how dramatic and quick an impact the Dietary Goals report would have on national policy.

Considering the controversy the report created when it was released, McGovern has a right to be surprised. Angry reaction from the industries most likely to be affected, if Americans began to eat as the goals advised, threatened to buy not only the goals but the senators who had signed the report as well.

Even though these vocal critics haven't gone away, their voices are being drawned out, and now, 2 1/2 years later, Dietary Goals have become the basis on which much of the scientific community has reached a consensus about the direction in which the American diet ought to be moving.

Within the last five months several significant events have set the course. On May 5, the American Society for Clinical Nutrition (ASCN), an extremely conservative group of scientists, released a report. The scientists were asked to rate the relationship between cholesterol and heart disease, between fats and heart disease, then cholesterol and fat in relationship to the disease; between carbohydrates, sucrose and heart disease, carbohydrates and diabetes, carbohydrates and dental cavities, alcohol and heart disease, alcohol and liver disease, salt and hypertension; excess calories in their relationship to obesity, hypertension, diabetes and heart disease.

If the evidence of the relationship were "rock solid," a total score of 100 was possible. And this is what happened:

Out of the possible 100 points the relationship between cholesterol and heart disease got a mean score of 62; fat alone got 58; cholesterol and fat together got 73.

The relationship between carbohydrates, sucrose and dental cavities scored 87; between alcohol and liver disease 88; between salt and hyptertension 74; between calories and obesity, hypertension, diabestes and heart disease 68.

The three other topics -- carbohydrate and heart disease, alcohol and heart disease, and carbohydrates and diabetes -- scored between 11 and 13 points, indicating the scientists couldn't find much connection.

While ASCN did not address the relationship between diet and cancer, Dr. Arthur Upton, director of the National Cancer Institute did earlier this week.

Upton told a senate hearing last year, "Scientists generally agree diet and nutrition . . . appear to be related to a large number of human cancers, perhaps approaching 50 percent." On Tuesday, Upton made some recommendations: maintain ideal body weight, reduce total fat intake, increase total dietary fiber, consume alcohol in moderation.

The findings of the American Society for Clinical Nutrition and of the National Cancer Institute have provided the signal needed by Department of Agriculture and Department of Health Education and Welfare to stop dragging their heels in developing dietary guidelines.

As Ellen Haas, director of the consumer division of Community Nutrition Institute (CNI), sees it: "Everything in government must be justified. Until now they thought there wasn't enough scienific research data to back up guidelines. But what has become apparent in the last year is that there has been a good deal of research in the medical and health communities so it is entirely possible to come up with dietary recommendations."

Because the Surgeon General's report on health promotion and disease prevention had come to the same conclusion in July didn't hurt. This report says that if Americans make some momentous changes in their diet and habits they can reduce their premature death rate by 20 to 35 percent in the next 10 years. Like Dietary Goals the report advises people to cut their intake of alcohol, salt, sugar, cholesterol and fat, especially saturated fats.

Then last week the National Institutes of Health held a two-day conference on nutrition education at which Dr. Mark Hegsted, who is administrator of USDA's Human Nutrition Center, discussed the ASCN report: "By anyone's evaluation the panel reports must be about the most conservative estimate of the situation that can be developed yet [but] the message does come through . . . They state that it is the responsibility of government officials to formulate policy from the evidence provided."

Hegsted, who played a major role in the development of Dietary Goals, said that ideally diets should be tailored to individual needs. Since that is impossible "general dietary instruction to reduce risk is necessary and appropriate in exactly the same way that general instructions are developed to reduce risk of nutritional deficiencies even though we know that there will be a marked difference in the benefits different individuals will gain from the consumption of any recommended level of a nutrient."

Hegsted must be smiling just a little. Two years ago he gave a speech at the first Community Nutrition Insitute nutrition conference, a speech he often repeated, explaining why Dietary Goals are sensible. He argued that even though all the evidence isn't in, there is no harm in following the recommendations made in the report.

At the third annual CNI nutrition conference, which concluded yesterday, Assistant Agriculture Secretary Carol Foreman, announced tentative USDA-HEW nutrition guidelines. They vary little from the Dietary Goals.

Both Hegsted and Foreman said they wish they offered a lot more practical advice on implementing the guidelines, but they are a beginning. "It's not nearly as specific as alot of us hoped it would be," Hegsted said in an interview. USDA blames HEW for the lack of more substantive progress.

Experts in the field of nutrition say that a national policy based on these guidelines would have a significant impact in a number of areas: food purchased for government feeding programs, foods permitted to be sold in school vending machines, requirements for nutritional labeling of food, regulation of food advertising and food production priorities such as encouraging production of leaner beef. Another obvious impact area would be nutrition eduction, not only what is being taught in schools, but what kind of financial committment the federal government is willing to make toward it. "Until now," Haas said, "the federal government's commitment to nutrition education has been insignificant. All kids get is industry material. If the guidelines have the imprimateur of HEW, USDA and the White House, it would serve to balance the current sources of information consumers receive. Today it comes mostly from food industry sources through ads."

Difficult as it has been to achieve a consensus for a national nutrition policy, turning theory into practice may be even more trying. Hegsted says moderation is the key word, but "what do we mean by moderate?"

"Beyond the need to assure adequate intakes of essential nutrients," Hegsted said, "dietary advice must be acceptable to the public . . . Extreme recommendations -- even if scientifically justified -- are not likely to be practically useful . . . consideration of food habits, the food supply, food preparation methods . . . must be used.

"Dietary advice is often so full of don'ts that the penalties appear to outweigh the benefits. We do not eat for nutritional benefits alone."

That is the challenge: translating general guidelines into menus and recipes people will put in their mouths; menus and recipes that taste good even though they have less salt, fat, cholesterol and sugar. It's easier said than done.