In the face of increasing medical concern about the size and structure of the American diet, despite humanitarian arguments for reduced consumption, despite record high food prices. Americans appear to be consuming more food than ever.

Statistics compiled by the U.S. Department of Agriculture for an annual survey that was scheduled for release this week show a sharp upward turn in both total and per capita food consumption during 1976. Preliminary figures placed the per capita increase at 3 per cent over 1975. Due to a number of economic and marketing factors, there was a slide in consumption that year. But if the new figures hold up, they will push per capita food consumption ahead of even the previous record year, 1972.

The sharp, unprecedented rise in food prices that began in 1972 led to a nationwide meat boycott and increased attention to food purchases and eating habits. The situation has provided a ready-made soapbox for those who would change the American diet. The culmination of their efforts to date was a strong policy statements issued this January by the Senate Select Committee on Nutrition and Human Needs.

It linked diet to heart disease, cancer, vascular disease, diabetes, arterioscleroisis and cirrhosis of the liver and recommended, among other steps, a 40 per cent reduction in sugar consumption, a 10 per cent reduction in fat consumption, a 50 to 85 per cent reduction in salt consumption.

"The question to be asked . . .," said Dr. Mark Hegsted, a Harvard University nutritionist who helped draft the report, "is not why should we change our diet but why not. What are the risk factors 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."

But early evidence indicates that in 1976 the American public was going just the other way. Not only are people eating more instead of less, they appear to be emphasizing some of the foods they are being warned against.

The Agriculture Department is expected to announce consumption increases in beef (7 per cent), pork (6 per cent), vegetable fats (7 per cent) and sugar (6 per cent). In terms of food energy, daily per capita calorie consumption was measured at 3,290. In 1975 the figure fell from the 1974 level of 3,280 to 3,210, the same as it was in 1967.

While vegetable consumption is also up (2 per cent) and poultry, which is less caloric than red meat, led all categories with an 8 per cent gain, that will hardly suffice for those who are dedicated to reversing trends in the nation's eating patterns.

At the American Meat Institute, statisticians have calculated an increase of 10.6 pounds per person in meat consumption from 1975 to 1976, despite a decline in the demand for veal and lamb.

This swing toward increased consumption was hinted at by a Super Market Institute survey conducted last July. "Consumers continue to maintain most of their 'coping with inflation' habits," the report concluded. ". . . There are, however, some signs of return to former ways."

Among them: a reduction in meal planning from 64 per cent of respondents in late 1975 to 55 per cent last summer; a reduction of those buying less meat from 59 to 50 per cent and of those buying cheaper cuts from 55 per cent to 47 per cent; a reduction in those serving less at family meals from 26 per cent in the winter of 1974 to 20 per cent and an even greater fall off in those who continued to cut down on entertaining.

Yet the consumer price index for all food continued to rise in 1976, a final figure quoted by the Meat Institute being 4.6 per cent.

Of course statistics can be misleading. The Agriculture Department and the Meat Institute, which uses only choice beef in its calculations, don't agree on the precise increase in meat consumption. And the "consumption" itself ready isn't; it is the "retail equivalent," that is delivered to retailers.The common assumption within the industry is that all beef produced is eaten and that the decline in meat consumption in 1975 was due to lack of supply, not pangs of conscience nor lack of money on the part of consumers.

"There is no real measure of what individuals actually consumed," said Betty Peterkin of USDA's Agriculture Research Service. "We don't know what the totals really mean. The intake of a person of certain age and sex is not known."

For this reason Peterkin and others in the nutrition field are anticipating the commencement next month of a year-long study funded by USDA that will send researchers into 15,000 homes for a week at a time. The researchers will, in Peterkin's words, "find out what foods are used up, what goes into the mouths of each member of the family, what's eaten there and what's eaten away" and come away with data for updated nutrition evaluations.

The last survey was conducted in 1965. Several supplemental studies, including one of 5,000 elderly homes, may be added to this year's.

In the meantime, pressure to involve the government more directly continues. "Maybe people have heard about the Select Committee's report on Dietary Goals," said Ellen Haas of the Community Nutrition Institute, "but few if any know what's in it. In the absence of a national nutrition policy relating health factors to consumption, we will continue to have increases."

Haas attacked what she called a lack of "meaningful education" on dangers of overconsumption and the government's role in helping produce, market and promote foods od dubious nutritional value. As goals for change she suggested a food grading system that would reflect nutritional quality, a revision in federal supports of agriculture to balance needs of producers with needs of consumers and more funds for nutrition research and education.

Richard Ling, who heads the American Meat Institute, said meat consumption will drop by 1979 because economic conditions have forced production cutbacks. "There will be shortages down the road," he said. "Pork was down in 1975 because there wasn't any more for people to buy. Itwas premature to see a change in eating habits. In the world as affluence has increased so has the demand for meat and never more than in this country. Somewhere it probably will level off, but I don't know when."

To Ling the Senate Select Committee's report and reaction to it "confused the public . . . The major result, as I see it, was to show the need for more research in nutrition." He feels the appropriate role for government to play in nutrition controversies will not be "clearly defined" for "a long time."

In the meantime there are numerous theories on why Americans continue to eat so much of what may be bad for them. While food price inflation continued in 1976, the rise was less dramatic than it had been earlier in the decade. People may just be tired of not buying.

Betty Peterkin of USDA suggests "food shopping is a question of habit.People don't change unless they develop a health problem, tire of a food or someone in the family doesn't like it. A certain amount of buying is for personal gratification or as a status symbol." Richard Ling suspect "a general lack of faith" in the charges against meat and other foods and asks, "notice how many people still smoke?"

Ellen Haas acknowledges the presence of a "leave me alone, I don't want to be saved" syndrome, but insists the dangers are real. "Somehow the message has got to get through," she said, quoting an inner-city woman with a family of 12 whose response to an Urban League survey about eating choices was. "I just go to the store and get food."