As the famine in Ethiopia eases, the largest American relief agency operating in that country has instigated an acrimonious dispute with the U.S. government -- the largest food donor -- over how much more food aid is needed to keep Ethiopians from starving.

Catholic Relief Services, an official arm of the American Roman Catholic hierarchy and by far the largest charitable organization distributing food in Ethiopia, argues that it will run out of food this July and that tens of thousands of peasants will be endangered unless the U.S. government commits more food.

"You are asking us to decide who will live and who will die," said Frank Carlin, country director for Catholic Relief Services in Ethiopia.

The U.S. government, however, maintains that CRS has designed its feeding program so that it will run out of food in July. It also charges that, while the number of Ethiopians needing relief food has declined sharply, CRS is using the threat of mass starvation to pry loose extra food aid from the government.

"CRS doesn't seem to share everyone else's view that the situation has improved . . . . They want to continue at high feeding levels when everyone else is scaling back," said Fred C. Fischer, chief official in Ethiopia for the U.S. Agency for International Development, in a recent telephone interview.

"We are concerned that they [CRS] are setting up a situation in which they could accuse the U.S. government and other donors of not providing the resources needed to keep their program going or to force us to provide resources that we don't have," Fischer said.

The dispute between Ethiopia's largest food distributor and its largest food donor has boiled over during donor meetings in Addis Ababa, the Ethiopian capital. There have been bitter and emotional exchanges between CRS and U.S. government officials.

AID pays for the food and its transportation but not the salaries of the CRS staff.

"CRS and the U.S. are going at one another," said a senior official with another large American aid agency operating in Ethiopia. "Everybody here is aware of the friction."

[In Washington, Director Lawrence Pezzullo of CRS met Friday with AID Administrator Peter M. McPherson and spokesmen for both described the session, on logistical problems in Ethiopia, as productive.]

The dispute has spawned charges by CRS country director Carlin that the U.S. government is limiting food aid because of its ideological distaste for Ethiopia's Marxist military government.

Carlin recently told the Catholic Bulletin, a U.S.-based Roman Catholic publication, that he found it "immoral" that the United States was withholding adequate food supplies from the Ethiopian people. He said the U.S. government was slow to respond to the Ethiopian famine in 1984 and did so only after being "prompted by the people. We are going to have to have something like that happen again."

CRS, in turn, has been accused by other relief agencies of trying to blackmail the U.S. government, which provides one-third of the donated food in Ethiopia, and of trying to maintain its famine-relief fiefdom in the face of decreasing needs and stiff competition for U.S. resources from other agencies.

Last year, CRS and its affiliated agencies fed about 2.1 million people a day and received 51 percent of the 440,000 metric tons of U.S. food shipped into the country. But as the number of people estimated to be affected by famine has fallen from 7.9 million last year to about 5.8 million this year, CRS has been allotted a smaller portion (41 percent) of the smaller overall total of American food aid. So far the United States has pledged 300,000 metric tons for 1986.

"This reduction in CRS resources reflects our view that there is a vastly improved situation in Ethiopia," said Fischer of AID.

He added that "CRS got such a large percentage of U.S. resources [last year] because it was the only nongovernmental organization on the scene with an established bureaucracy. Today there are several NGOs [nongovernmental organizations] with infrastructures and whose feeding programs are every bit as good as CRS."

CARE, World Vision and the U.S chapter of Save the Children all increased their share of American food aid in this year's allocation.

In the Catholic Bulletin, Carlin said that CRS' share of U.S. food had been cut because "of our strong stand" on famine issues.

Fischer maintains that CRS has refused to adjust its feeding program to reduced food-aid needs following the December and January harvest in Ethiopia.

"Many NGOs other than CRS have scaled down their feeding programs substantially or in some cases suspended them entirely for this period after the harvest," Fischer said.

The International Committee for the Red Cross has suspended 50 percent of its feeding in Eritrea. Save the Children temporarily has halted feeding in the northern Shewa region. CRS, however, has continued its existing feeding program. "We have no choice," CRS spokesman Kevin Delany explained. "You can't go on half rations, because you would be endangering people."

CRS says that it must calculate food needs based on the number of hungry people in its programs and not on overall estimates of Ethiopia's food deficit.

"A U.S. cutback based on an overall crop assessment puts into danger people in our programs who need food and are oblivious to the national cereal picture," said one senior CRS official based in Nairobi.

According to the U.N. Food and Agriculture Organization, the recent middling crop in Ethiopia left a need in 1986 for about 900,000 metric tons of food aid. An official of the U.N. Office for Emergency Operations in Ethiopia said about 600,000 metric tons of that food has been pledged by international donors.

In addition, the Ethiopian government, using a foreign-exchange windfall from high coffee prices and from the massive international famine relief effort itself, has contracted to purchase 300,000 metric tons of food from the Australian government. According to western diplomats in Addis Ababa, Ethiopia now is negotiating to buy an additional 100,000 to 200,000 metric tons of food from Canada.

Fischer said that if the Ethiopian government makes the additional purchases, the country will come close to meeting its food needs without any more aid than already has been pledged. "We think it will be a whole new ball game if that comes through," he said.