The Soviet Union has pledged 250,000 tons of emergency grain to Ethiopia -- more than the United States has so far offered -- to help feed 5 million Ethiopians facing starvation from drought in East Africa.

The unusually large pledge, apparently calculated to slightly surpass the American contribution of 247,000 tons, has caught the U.S. government by surprise because the Soviets usually import foreign grain for themselves, and have never made such an offer to Ethiopia before, despite the fact that they strongly support the Marxist regime in Addis Ababa.

U.S. officials said the Soviet pledge might be the largest ever made by the Soviet Union to a Third World nation.

It has touched off debate among nine American private relief groups, which distribute a large portion of international relief aid to Ethiopia, about whether they should handle Soviet grain if asked to do so.

A World Vision official said his organization was concerned about the impact such involvement might have on fund-raising efforts, which he said were in trouble from the latest Ethiopian famine crisis.

"We're still sorting it out," said Thomas Getman, World Vision's director of international affairs.

He said the Ethiopian government's Relief and Rehabilitation Commission, which will take charge of the Soviet grain, has not yet asked the private groups to help transport and distribute the grain inland. But he said there is "no way" the commission could do it alone.

"They will finally have to come and ask us to help," he said.

A spokesman for the U.S. Agency for International Development (AID) said the United States welcomed the Soviet donation and would have "no objections" if American private voluntary groups decided to help distribute it.

"We naturally assume the Soviet Union will fund the cost of its distribution just as AID has done for its aid," said spokesman Bart Kull. He said AID estimated the cost of distribution at $25 million.

The Soviet Union, Ethiopia's major foreign ally, was widely criticized during the 1984-85 famine emergency for failing to provide much food or other assistance. Instead, Western donors, led by the United States, donated the bulk of the one million tons of food sent to cope with the famine and provided for most of the transportation inland.

This time, it appears the Soviets are determined to head off similar criticism and take a leading role in helping to cope with the emergency.

U.S. officials say it is not clear where the Soviets are getting the grain promised to Ethiopia, but say it could come either from Soviet domestic stocks or from Argentina. However, Moscow recently purchased 300,000 tons from Saudi Arabia, which has recently become a wheat exporter and is located across the Red Sea from Ethiopia.

The Soviets made known their pledge in Addis Ababa Jan. 26 and said the wheat would arrive in Ethiopia before July. The Soviets are also airlifting to Ethiopia 15 tons of medicines, 10 tons of food concentrates and a ton of children's formula.

To date, the U.S. pledge of 247,438 tons of food is worth $88.3 million, including transportation costs, plus $6.6 million for other inland transportation needs. Other Western nations have pledged 441,454 tons, bringing the total to almost one million tons.