KHARTOUM, SUDAN -- Harassed by rebel attacks, Sudan's hard-pressed Army apparently is depriving famished civilians of food and protection, according to diplomats and relief workers, as the civil war in the south ends its fifth year.

These diplomats and relief workers, long reluctant to denounce military excesses in the south for fear of compromising relief operations with a sensitive government, have begun providing what they say are examples of the worst cases.

{Khartoum authorities reportedly refused Monday to reconsider their decision to expel four foreign relief organizations working in the south, according to the British Broadcasting Corp. The four are World Vision, The Association of Christian Resource Organizations Serving Sudan, the Lutheran World Federation, and the Swedish Free Mission.}

The sources charged that in Wau, in the south's westernmost province of Bahr el Ghazal, Gen. Abu Quroon Abdallah, commander of the Wau garrison, personally masterminds atrocities against civilians, including food deprivation and crucifixions.

In what one source called a "continuous massacre," between seven and 10 civilians allegedly are killed daily in Wau, where the Army and Fertit tribesmen armed by the military prevent any movement in or out of town by approximately 30,000 Dinka refugees.

Sudanese officials, asked about these reports, refused to comment.

The general's tactics, diplomats say, reflect the frustrations felt by the northern, largely Moslem, Arab-led government and Army toward southerners following a series of battlefield defeats during the current dry season. The armed forces normally dominate the dry-season fighting because of greater mobility.

With each succeeding setback, northerners renew charges that the south is collectively responsible for the rebellion led by an American-educated Dinka, John Garang, who was an Army colonel before he deserted to form the Sudan People's Liberation Movement.

Based in neighboring Ethiopia, the rebel movement and its 30,000-man fighting force rely for support principally on the Christian or animist southerners, who make up an estimated 8 million of Sudan's 22 million population.

Garang's main war aim is to wrest control of the central government from the northerners, but he denies their charges that his real goal is a separate southern state.

In Wau and in Aweil, Malakal, Juba and other major centers where southern civilians have sought food and protection from the war, relief workers said the Army has been reluctant to provide prompt, regular armed escorts for convoys of food relief trucks, trains or river shipments.

With 46 barges of commercial and relief food waiting since October at the White Nile port of Kosti, the Roman Catholic bishop of Malakal warned in a Jan. 25 letter of "imminent catastrophe," with "the majority of the population reduced to extremity" because no food had arrived for a year.

Noting that "military planes were flying in frequently," Bishop Vincent Mojwok said "it should also be possible for food relief planes to come." But no flights or barges have arrived in Malakal, in Upper Nile Province, where severe drought along the east bank of the White Nile has sharply curtailed food production and swollen the town's population with 40,000 displaced persons.

A lack of armed escorts also has shut down the railroad system since October south of Aweil, in the heart of a densely populated Dinka area leading south to Wau, according to relief workers.

Relief officials say long delays in providing armed escorts for convoys often are caused by Army officers and Arab merchants maneuvering to drive up the price of food and other goods in southern cities.

In the past year, Garang has won over key tribes that once refused to join his movement because of traditional suspicion of the Dinka.

For example, the Anyanya Two Movement, a group of Neur tribesmen whose elders led a major rebellion against Khartoum from 1955 to 1972, last year stopped fighting for the Army and went over to the rebels. Their defection created serious problems for the Army in Upper Nile Province. North of Juba in the past year the Mundari tribe also went over to Garang.

Farther south along the Kenyan and Ugandan borders in Equatoria Province, Garang also won over Toposa cattle grazers in the east and Kakwa farmers in the rich farming area to the west. Garang was successful in part by recruiting local youths last year, training them in Ethiopia and sending them back home in charge of rebel units.

Diplomats said the winning of these hearts and minds had enabled Garang to increase harassment of vital roads leading to Kenya and Uganda and to capture an important Army garrison at the district capital of Kapoeta last month. That cattle grazing center, with 80,000 inhabitants, was the largest city to fall to the rebels.

With the approach of the rainy season, a five-foot cover from elephant grass and impassable roads, the rebels are expected to tighten the noose around Juba, the southern capital, more than in previous years.