The United States and Ethiopia have reached an agreement that is to provide another 50,000 tons of emergency food aid to starving people in the drought-stricken African nation and guarantee its delivery, officials of both countries announced yesterday.

In a major breakthrough, the food is to be sent directly to the Ethiopian government relief commission, which is to allow private international relief organizations to supervise distribution inside Ethiopia. Delivery costs are to be divided equally between the two nations.

The Ethiopian government has agreed to give the food top priority at port areas and provide "a substantial number" of trucks to deliver it, according to M. Peter McPherson, administrator of the Agency for International Development. Tons of food have rotted at Ethiopia's Red Sea ports for lack of means to move it inland to the estimated 6 million people facing starvation because of the long drought. U.S. insistence on delivering the food to private groups rather than to the notoriously inefficient government commission had also stalled delivery.

Ethiopia's population of 33 million is spread thinly over an area twice the size of Texas. As many as 40 persons have been dying daily at relief centers in what United Nations officials have called the worst human disaster in recent African history.

The joint agreement said further food aid could be provided if the latest shipment is distributed "efficiently and in accordance with stringent U.S. government regulations." The United States also is to "consider" requests for deep-water drilling rigs, increased medical supplies and new port equipment to unload ships.

McPherson said that existing AID funds are adequate to cover the new program and that new funding would be requested next year to continue the aid as long as the drought continues.

The agreement raises the total U.S. aid commitment to about $60 million, including $12 million for the new food and $2.4 million to charter two L100 cargo planes to airlift food to remote areas for at least two months.

About 80,000 tons of U.S. food aid already has been sent.

The Ethiopians also have agreed to make certain that food is provided to Eritrea and Tigre provinces, where rebels have been trying to secede from the country for several years.

Dawit Walde Giorgis, head of the Ethiopian Relief Commission, appeared with McPherson at a surprisingly amiable joint news conference, considering abusive rhetoric exchanged recently by the two nations about famine relief.

Their two days of talks, McPherson said, produced "a positive agreement that in fact can save people's lives." Giorgis expressed gratitude for "an overwhelming response" from American citizens offering private aid.

Ethiopia's leftist government, which recently adopted a one-party communist political and economic system, had complained bitterly that U.S. aid offers were insignificant. Giorgis said yesterday that the Soviet Union has sent trucks, 12 planes and 24 helicopters to help deliver food and that he found the U.S. response encouraging. "We hope it continues," he said.

State Department officials, including McPherson, have countered that, rather than feed its people, the Ethiopian government spent millions last month to celebrate the 10th anniversary of the military coup that brought it to power.

Giorgis said that spending for "our own humble display of lights" totaled $1.2 million and that another $8 million had been used to build a hall for the new congress.