Rail and trucking delays in shipping of American-donated grain are threatening millions of people in western Sudan with famine, relief workers and U.S. officials said today.

The officials said they had notified the ruling transitional military council -- which seized power from president Jaafar Nimeri three weeks ago -- of a five-week interruption in what had been biweekly rail shipments of sorghum. But no action has been taken to reestablish the service, they added. The line runs from Kosti on the White Nile River to Nyala, 590 miles to the west in Darfur Province.

In Kordofan Province, just to the east, a wrangle over trucking contracts had interrupted deliveries of grain from Port Sudan on the Red Sea, according to relief workers. That dispute is now settled, but only 5,000 tons of an expected 125,000-ton shipment due between April 1 and May 18 have arrived, they added.

Additionally, relief workers reported that military officials in the Kordofan capital of El Obeid were refusing to distribute 10,000 tons of grain until the 47,000 Sudanese in a nearby refugee camp went home or moved further south.

Prompting the military command's tactics were fears that the camp's inhabitants constituted a security risk to El Obeid's settled population, the relief workers said.

The military apparently was mindful of a riot further south in a railway depot at Kosti last week in which as much as 20 percent of grain stockpiled for eventual rail shipment to Darfur Province was stolen by hungry Sudanese.

Grain trucked in from Port Sudan has been temporarily stockpiled behind barbed wire. According to U.S. officials, the grain is visible to hungry Sudanese, who have deserted the countryside in search of food. U.S. officials here said they were at a loss to explain the interruption in rail deliveries of sorghum to Darfur Province. But they suggested that the general manager of the state-run railways or the divisional director in Kosti were responsible.

When the grain trains were stopped, railway officials cited a shortage of spare parts for locomotives and other rolling stock. But a U.S. offer to fly in spare parts under a $3 million emergency fund evoked no positive response, the officials said. They noted that general merchandise trains were operating normally on the line.

So far, there has been no starvation in Darfur, which borders Chad and Libya, because relief workers are distributing stocks of sorghum warehoused in Nyala and other centers, the officials said.

Noting that important amounts of grain must be in place in Darfur towns before the June rainy season makes road distribution all but impossible, one official said, "Unless train service resumes before then, a lot of people are going to starve."

American-donated grain is feeding an estimated 3.5 million Sudanese in Darfur and Kordofan provinces. Altogether, about 20 percent of the 22 million Sudanese are receiving the food. Grain is trucked directly to Kordofan without any rail shipment, but officials said there are not enough big, desert-equipped trucks to do so for Darfur.

Since U.S. grain began arriving in Port Sudan last November, relief workers have worried about violence breaking out among hungry Sudanese who watch truckloads of sorghum heading west, where U.S. efforts are concentrated.