Ethiopian farmers are facing a critical shortage of seed, according to famine relief specialists, that must be resolved by international donors and the Ethiopian government within three weeks if the drought-plagued country is to grow food this year.

The Ethiopian government is said to have enough seed in its warehouses to supply the half million farmers who have nothing to plant. But thus far, it reportedly has kept the seed in reserve to feed the Army and people in cities.

These specialists say failure to resolve the seed shortage, which the Ethiopian government and international donors have neglected in the rush to bring food aid into the country, would mean a need for continued massive shipments of aid again next year to prevent widespread starvation -- even if there are rains.

The next weeks are deemed critical because the government needs up to two months to distribute the seed now stored, and the last chance for planting comes in late June and early July.

Donors around the world have given or pledged $760 million worth of aid this year to Ethiopia, where 7.9 million people are threatened by famine. The United States, by far the largest donor, has approved $165 million in aid since October.

"No one is going to be willing to spend this kind of money next year. By getting seed to farmers we are talking about saving famine victims who are capable of saving themselves," said Donald Henry, an agricultural economist and consultant to the U.S. Agency for International Development and Catholic Relief Services.

Henry said that solving the seed shortage will help about one-third of the famine-affected peasants in Ethiopia -- those in government-controlled areas who have remained on their farms while receiving relief food. It will not help those peasants who are in relief camps or in rebel-controlled areas in the north.

"There is a capability, however, for self-sufficiency in Ethiopia, and that opportunity is going to slip by unless something is done within the next two weeks," said Henry. He recently returned to Washington from two months in Ethiopia, where he investigated the seed shortage.

Officials at the State Department, AID and two major private voluntary relief organizations operating in Ethiopia agree with Henry's assessment of the urgency of the seed problem. Two weeks ago, at a special United Nations conference in Geneva on African famine relief, Kurt Jansson, U.N. assistant secretary general for emergency operations in Ethiopia, was directed to return to Addis Ababa to try to resolve the seed shortage.

U.N. officials are to meet with donor countries this week in Rome to try to raise $185 million to deal with seed shortages and other planting problems for the 20 drought-affected countries in sub-Saharan Africa.

In Ethiopia, the specialists say, a solution to the seed shortage is complicated by growing conditions and crops, and by donors' failure to coordinate.

Not just any seed will grow in Ethiopia, with its high-altitude yet tropical terrain, where some farms are 5,000 to 10,000 feet above sea level. Most seed grain requires lower altitudes and more than the 12 hours of daily sunlight Ethiopian croplands receive. Seed for one major Ethiopian crop, teff, from which a breadlike food staple is made, exists nowhere else.

After three years of drought and one year of severe food shortage, most seed grain in Ethiopia is believed to have been eaten. Only the government has enough seed to plant this year's crop.

The government, however, is also being squeezed by the country's severe shortage of food. It reportedly has little foreign exchange to buy food on the international market and almost all donated food is earmarked specifically for famine victims -- not for government institutions.

Given the need to feed Ethiopia's large Army and make food available in cities, officials in Addis Ababa have been unwilling to part with their seed grain. While in many developed countries, seed grain is specially treated and inedible, seed and food in Ethiopia are the same thing.

The proposed solution is to swap imported food for domestic seed. International donors would give the Ethiopian government processed food or grain as a substitute for its warehoused seeds. The seed would then be shipped out to about a half million Ethiopian farmers. According to a senior AID official in Washington, Janssen is meeting in Addis Ababa to work out such an agreement.

The amount of seed involved is estimated by U.S. sources at about 30,000 metric tons, worth about $17 million, compared with 100,000 metric tons per month of food that has arrived in the country since the beginning of the year. An AID official here said the investment in seed could allow Ethiopian farmers to grow their own food and save donors hundreds of millions of dollars in aid next year.

The official said, however, that the United States will not help resolve the seed shortage. "It is recognized by the U.N. and other donors that it's probably not best for the United States to get in there and coordinate the seed problem because of the polemics that have transpired in the last few months," the AID official said.

Ethiopia, the Soviet Union's closest African ally, and the United States have continued to exchange recriminatory rhetoric even as U.S. aid has surpassed that of any other donor.

A senior State Department official said recently that U.S. food cannot be used in the food-for-seed swap because "it goes against all our rules and regulations . . . . You can't use disaster food to feed people in cities."

Rep. Mickey Leland (D-Texas), chairman of House Select Committee on Hunger, objected to this interpretation of U.S. law.

"The people at AID should use a little vigor and imagination in helping to make seeds available now during the planting season," Leland said. "Otherwise, we can only envision a continuation and worsening of famine conditions."

Along with the U.S. government, American private voluntary organizations operating in Ethiopia have been reluctant to swap their food with the Ethiopian government for its seeds.

"I don't know if PVOs [private voluntary organizations] have sorted out this problem for themselves," said Carol Capps, an executive here with Lutheran World Relief, an agency operating in Ethiopia. "Donors are traditionally concerned about the use of their food, and want to ensure that it gets to people who need it most, not to soldiers."

Failure to resolve the seed issue has already prevented Ethiopian farmers from planting for the so-called "short rains," a brief growing season that began last week with the coming of rain in some parts of the country. "That is an opportunity that has passed," said economist Henry. The short-rains planting normally produces about 10 percent of Ethiopia's total crop.

"We still have time to get seeds to farmers for the next planting," said Henry. "If we fail, who is going to pay for relief aid in 1986 for the 500,000 farmers who didn't get seed to plant this year?"