The United States proclaimed its support today for a world food security system, including a grain reserves stockpile, as part of the international arsenal in the war against hunger.

U.S. Agriculture Secretary Bob Bergland's statement at the opening of a five-day conference of the United Nations World Food Council marked a reversal by the Carter administration of the previous U.S. policy of opposing creation of an international food reserves system.

Bergland said "food must be an area of international cooperation, not international conflict," but he emphasized that food security also is not the sole obligation of the United States for few nations.

He said the United States was hopeful the International Wheat Council meeting in London next week wouldlay the foumdation for negotiations on an agreement which would include a coordinated system of nationally held food reserve stocks.

Bergland said a world food security system should include a reserve stock mechanism to reduce wide fluctuations in market prices, cost-sharing in the food stockpile by both importing and exporting nations and provisions to prevent interruption in grains trade. He said ways would have to be found to assist poor countries to pay their share of the reserves cost.

Such a system, he said, would be a significant step forward in preventing a recurrence of the widespread famine which killed hundreds of thousands during the world food crisis of 1972-74.

Bergland noted that the United States had recently agreed to contribute up to 125,000 tons to the emergency international food reserve set up at the World Food Conference in Rome in 1974.

The U.S. message appeared to be directed as much at consuming nations such as Japan and the Soviet Union as it was at the developing countries.

The Third World nations have been seeking assurances that the reserves would be cushioned from high prices at times of shortage, while simultaneously seeking commitments that their own food exports would be guaranteed "fair" prices during periods of surplus or shortage.

The World Food Council was created at the United Nations' World Food Conference in Rome in 1974. It has attempted to persuade governments to increase domestic food production and corporate international to prevent scarcity and high prices.

Efforts to establish an international food reserve have made little headway, although officials of the World Food Council have declared that some kind of a reserve is essential to long range stability.

World Food Council officials say reserves and price provisions are linked closely. Reserves would be accumulated when prices dropped to the minimum level and released if they went above the ceiling. They also would be available to meet sudden emergencies such as famines. But the reserve question is highly controversial because many farmers fear that such stocks depress prices. Nevertheless, as stocks of unsold wheat build up -- as they have recently -- reserves gain appeal as a possible new outlet for the grain.