Declaring that as many as 800 million of the earth's poorest people have too little to eat, a presidential comission yesterday called the United States to lead a worldwide fight to eradicate hunger in the next 20 years.

"This commission recommends that the U.S. make the elmination of hunger the primary focus of its relations with the developing world," Chairman Sol M. Linowitz said in a letter accompanying the group's preliminary report to President Carter. "We are convinced the goal can be met, if the struggle against hunger receives the priority it deserves."

In accepting the report from the Commission on World Hunger, President Carter enthusiastically endorsed its recmmendation that the United States take the lead on the hunger issue.

"This is an opportunity for our nation to embark upon an exciting, challenging effort to alleviate the problem of world hunger," Carter said at the White House. "It is obvious that our nation is better off if hunger can be eliminated in nations not as fortunate as we."

In delivering its report to the president, the commission said that world hunger has worsened since the last global food crisis five years ago. In 1974, the commission said, the world's hungry totaled 740 million, a number that has grown by 60 million even after three straight years of what it called good world harvests.

Reasons for the rise range from continued population increases in developing countries to a worsening of poverty conditions in the same countries.

"The world hunger problem is getting worse," the commission said flatly. "A major crisis of world food supply -- of even more serious dimensions than the present energy crisis -- appears likely within the next 20 years, unless steps are taken now. . . ."

The commission said the first step should be a doubling of the $1.5 billion the United States supplies every year to developing countries in the form of technical and economic assistance to help them grow more food for their people. The commission did not advocate that the United States feed the world's hungry.

"It could not succeed at such a mission and should not try," the commission said. "The principal cause of world hunger is not the occasional dramatic disaster that captures world attention, but the enduring condition of subhuman poverty that afflicts as many as one in five members of the human family."

Saying that one person in eight suffers malnutrition "severe enough to shorten life, stunt physical growth and dull mental ability," the panel said "the major world hunger problem is not famine or starvation, but the less dramatic one of chrnoic undernutrition."

Chronic undernutrition results when people get 60 to 70 percent less calorie and protein intake them they need to lead healthy lives. The effects of daily undernourishment, the commission said, are diseases that shorten life and make life a chronic hardship.

"Although repeated shortages of calories may receive less attention from the news media than outright starvation they take a far greater toll in human lives," the commission said in estimating the world's undernourished at anywhere from 450 million to 1 billion. "The wide variation of these estimates should not obscure the tragic reality that every day of their lives hundreds of millions of people do not get enough to eat."

The commission said the major cause of world hunger is not recurring famine or political calamities like the one starving 4 million Cambodians right now, but rather poverty.

"The struggle against hunger is a struggle for self-reliant economic development," Linowitz told Carter. "The members of this commission are convinced that the U.S. has a decisive role to play in the elimination of world hunger."

Linowitz said the elimination of world hunger "will require a major effort on the part of the developing nations themselves, a high degree of international cooperation, and the significant participation of the U.S."

The commission said the U.S. aid to developing countries for economic and agricultural help "is pitifully small," less than one quarter of one per cent of the nation's gross national product and a figure that places the United States no better than 12th in the world.

The panel urged that the United States double its nonmilitary foreign aid in the next three years and triple it in the next 10 years to "help others feed themselves." One of the most important reasons for such an increase was to improve world security.

"While recent international events have heightened concern for national security," Linowitz said to the president, "we as a people must understand that the U.S. and other developed countries can never by secure in a world of widespread hunger and intensive poverty."

Carter told the commission that there had been "too much concentration on military aid in the past. We need to divide our commitments better. Our people need to be made aware of the benefits to our country for this effort to alleviate hunger in the world."

One commission member said that if the United States had given the world more food instead of guns, it might find its embassies still intact instead of burned.

"We have put too much emphasis on arming the world, and too little on food," D. W. Brooks, former chairman of Gold Kist Corp. of Georgia, said at a news conference. "And we don't believe we'd have all our embassies being burned if those people felt we were helpful to them and their food every day."

Two-thirds of the world's hungry live on the subcontinent of India, the commission said, spread out over India, Bangladesh, Pakistan, Afghanistan, Nepal, and Sri Lanka. Much of the rest live in Indonesia and the arid lands of Africa just below the Sahara Desert.

While 800 million live with chronic hunger, the commission said, another 1 billion live in such near-poverty conditions that they're on the verge of hunger. The commission placed most of these people in Africa and some in Haiti, Bolivia and Brazil.