NAIROBI, Jan. 4 -- Anti-government rebels in the East African country of Sudan have issued a deadline of Jan. 15 for international relief officials to begin operating a food barge intended to serve hundreds of thousands of civilians suffering from hunger and disease in rebel-held territory along the White Nile river.

The barge, currently under control of the International Committee of the Red Cross, has been idle for more than five months while relief officials unsuccessfully have sought approval from the Sudanese military government to operate it.

If the $1 million vessel is not moved by the deadline, the rebels say, they will take control of it themselves.

In a letter late last month to Red Cross headquarters in Geneva announcing the deadline, relief officials connected with the rebel Sudanese People's Liberation Army said, "It is very unfortunate that the government of Sudan has acted to prevent this barge from moving. . . . We, however, feel a moral obligation to save lives."

The barge, called the Red Cross II, was paid for by the government of Norway and specially designed to traverse the marshlands of the White Nile in the rebel-held south of Sudan. It was intended to ferry thousands of tons of food and medical supplies several hundred miles downstream to an estimated 500,000 civilians in the White Nile valley, and to help open up badly needed relief routes to two provinces frequently plagued by famines.

International relief experts estimate that as many as 8 million civilians in Sudan will be affected by a region-wide famine this year caused by drought and war.

The relief barge has been tied up both by bureaucratic hassles and the Red Cross's mandate, which requires approval for its operations from both sides in any conflict. The Khartoum government fears the vessel will by used by the rebels to transport weapons, and its refusal to approve its operation has effectively stalemated the Red Cross project.

The predominantly Christian and animist southern rebels, who are fighting for a greater share of power in the Moslem-dominated government in the north, deny that they will transport weapons on the barge, but they refuse to allow the Red Cross to comply with a government request that the barge be sailed to territory controlled by government troops.