The specter of famine is once again stalking the parched Horn of Africa, but civil wars, political arguments and the rising cost of fuel could prevent food aid from reaching millions of people in need.

Five years after one of the worst famines this century, the rains have failed for the second year in a row, decimating crops across a broad swathe of the Sahel from Ethiopia through Sudan and Chad to Niger."There has been a major failure of the rains across a broad band of the Sahelian zone. It may go as far across as Niger, and all those countries may need assistance," said Paul Mitchell of the United Nations' Rome-based World Food Program.

Mitchell said crop assessments were currently taking place and their results would be available within a few weeks, but already a dramatic picture of need was emerging.

"1991 will certainly be worse than 1990, which was already bad. But it is probably too early to say how bad it is because no government has appealed yet," he said.

Mitchell said at least 3 million people risk starvation in Ethiopia, mainly in the war-torn north of the country, and at least 2.5 million in Sudan.

Aid organizations are preparing for a massive relief operation on the scale of 1984-85 when up to a million people died in northern Ethiopia alone.

But political factors threaten to delay its start.

In Sudan, the embattled military government of Gen. Omar Hassan al-Bashir is resisting Western pressure to declare a famine.

In Ethiopia, the government and rebels are squabbling over proposals to use the rebel-held port of Masawa to import food aid.

"Opening up Masawa will be absolutely critical in 1991," the WFP's Mitchell said. "All the other supply routes are fragile and could break any time."

Mitchell said the number of people needing food aid in Sudan could reach 6 million in government-held areas alone.

Famine also threatens large areas of southern Sudan controlled by the rebel Sudan People's Liberation Army.

"One of the worst-hit areas - Bahr el Ghazal - is receiving only 14 percent of its food aid requirements," said Egil Hagen of Norwegian People's Aid, which sends relief supplies into rebel-held areas of southern Sudan from Kenya.

Hagen said it was impossible to say how many people faced starvation in southern Sudan since many had fled to escape the fighting. He accused the government of using food as a weapon to try and depopulate rebel areas.