A panel of experts has told President Carter that the world hunger problem can not be solved just by increasing food production, that countries also must make broad changes in their social and economic structures.

The findings were reached after a two-year study of the hunger issue by a panel organized by the National Academy of Sciences. Although the report appeals for more government spending for research, it also gives unusual emphasis to the need for non-scientific solutions.

American policy makers traditionally have stressed the need for foreign countries to produce more food, and this country has spent billions of dollars on scientific research to increase grain yields. But the situation that exists in the world this summer shows that more food alone is not the answer. American farmers and grain storage depots are still holding 30 million tons of unsold wheat from the 1976 harvest. Yet the panel's study found 450 million people suffer from malnutrition.

Tens of millions of these people have no money to buy food, or food has not reached them.

The 153-page report notes, for instance, that "the major immediate cause of hunger is poverty." It emphasized that a solution to the food problem will require better food distribution, more even incomes among populations, trade reform and changes in tax, farm credit and land ownership structures that discourage local farmers from growing more food.

Contrary to what many people assume, food production has increased slightly faster than population in the developing countries in recent years. Yet the study declares: "The rapid population growth and inequitable income distribution apparently have combined to increase the absolute numbers of malnourished people."

"We could double food production tomorrow and we still wouldn't solve the problem," said Harrison S. Brown at a press conference last week.

Brown, professor of geochemistry, science and government at the California Institute of Technology, led the study that interviewed 1,500 people and drew upon the talents of social scientists, food marketing experts, scientists and demographers.

It called for the United States to spend $210 million to $230 million more a year over four years for nutrition, plant genetics, population and food production research. Included would be an increase of $120 million in the first year for more basic research by the Department of Agriculture. But, significantly, the study also urged a "sharp increaset" in social science research.

"Science and technology alone cannot improve the world food and nutrition solution," it said. "Political will" holds the key to doubling food production in developing countries by the end of the century. That will be necessary to avoid famine and political upheaval, Brown said.

The United States will have to provide a substantial amount of the food that will be needed in wealthy countries as well as developing ones. However, farmers have been getting less grain an acre, on average, since 1972. Corn yields, for instance, have dropped sharply, perhaps because farmers have used less high-priced fertilizers.

Food deficits abroad are likely to have a heavy political impact, according to Brown. He said that "the prospects for urban violence will increase in this time" as unemployed city dwellers fight for the food that is available.

Brown also warned that the United States has a vital vested interest in a solution to food shortages overseas. For as the demand for American food increases, food prices are likely to rise in the United States, he said. Brown was cautiously optimistic that a generation could be achieved.

The report, called "World Food and Nutrition Study," was prepared over two years by a committee picked by the academy's National Research Council. About 1,500 experts were interviewed or consulted here and abroad.

The final document warned indirectly against expecting too much from the "Green Revolution" - the name given to new, high-yielding rice and wheat varieties requiring large amounts of irrigation and fertilizer.

"The Green Revolution is a good example of the kind of complexity we're talking about," said Brown. "When the price of crude oil went up by a factor of four it had a bad effect on the Green Revolution" because it required large amounts of energy to produce nitrogen fertilizer from petrochemicals and run irrigation pumps.

The report urged that more money be spent on fundamental research, especially plant genetics which could lead to increasing food output at low cost and without large amounts of new energy.

For instance, plans now capture only 1 to 3 per cent of the sun's energy striking their leaves. Scientists are studying the process of photosynthesis to see if plants can become better "solar factories."

Another way of increasing plant output would be to develop species of corn that can draw their own nitrogen supples out of the soil, the way soybean plants already do.