Eritrea; Feuds sap rebels' strength; AFRICA'S LONGEST WAR SPUTTERING

In an isolated desert camp on an ink-black night, Eritrean guerrilla leader Ahmed Nassir admits his drive to ''liberate'' Eritrea from Ethiopia is sputtering.

He says the Eritrean war for independence - waged since the former Italian colony was integrated into Ethiopia in 1962 - is stymied by feuds and fighting among the Eritreans themselves.

''It is a serious problem,'' says Mr. Nassir, who is seated on a broad woolen camel blanket in the desert sands. ''We should be fighting the Ethiopians. Not among ourselves. This unnecessary bloodshed must stop.''

It is a situation the Ethiopian government has cunningly exploited.

Separatist rebels almost took control of the territory four years ago. Weakened by internecine strife, however, they were forced into the mountains between Eritrea and Sudan by Ethiopian troops equipped with new Cuban and Soviet arms and supplies. Only the small town of Nafka, about 60 miles from the Sudanese border, is in rebel hands now.

Mr. Nassir, chairman of the Eritrean Liberation Front (ELF), says he has made repeated attempts to come to terms with the main rival Eritrean separatist organization, the Marxist-Leninist Eritrean People's Liberation Front (EPLF). But the EPLF seems to have no desire to end the quarrel.

Last summer, fighting between the two factions forced some 2,000 ELF troops and supporters to seek refuge across the border in Sudan, where they were disarmed by the Khartoum government.

In the past year, the Ethiopians have pressed home their military advantage against the separatists - especially against the EPLF, believing it is more concerned with eliminating its rival than confronting the government.

Ethiopian forces frequently bomb and strafe provincial villages and farms in retaliation for rebel attacks. Eritrean youths, who could bring new strength to the guerrilla organizations, are often pressed into the Ethiopian Army and sent to other regions, such as the Ogaden, to repress rebels in other secessionist wars. Dissidents are sometimes arrested and sent to prison or ''re-education'' camps.

According to newcomers among the 450,000 Eritrean refugees in Sudan, Ethiopian government repression continues and popular resentment toward the Dergue (the ruling communist regime) runs high.

This resentment fuels the rebels' resolve, despite what they perceive to be stagnating international interest in their plight and despite reported war fatigue among many ordinary Eritreans.

The refugees in Sudan - particularly those in Kassala, who have swollen that market town to twice its normal size - seem demoralized. Faced with an uncertain future, many suggest that a compromise with Ethiopia's leaders might not be so bad after all. Some say they are willing to recognize Addis Ababa as their national capital if they are granted some autonomy and if democratic rights are respected.

''The world must bring pressure on the Dergue to give us our rights,'' said an exasperated refugee in Khartoum, who feels people have forgotten about the secession war.

''Eritrea is a UN responsibility. Why doesn't the UN step in and stop this fighting?'' he asks. And a few liberation front sources indicate they would be willing to attend a UN-sponsored conference.

Some sources say that sooner or later even the Dergue may be willing to negotiate, for this war - and resistance in Tigre, the Ogaden, and among the Oromos south of Addis Ababa - is draining Ethiopia militarily and economically.

The Army is far stronger than the Eritrean rebels, but it has sustained some serious loss of life in battles against the EPLF, which recently has been helped by the Tigre People's Liberation Front (TPLF).

Ethiopian forces firmly control Eritrean towns, but not the countryside, where guerrillas strike hard at convoys and military outposts.

Both Eritrean guerrilla groups say they get most of their weaponry from captured materiel, but substantial supplies are known to come from outside countries.

Saudi Arabia and some of the Gulf nations have assisted the ELF in the past, but the length of the conflict and new interest in improving relations with Ethiopia have substantially dried up these sources, according to some reports. The EPLF continues to benefit from Iraqi and Syrian aid.

Refugees and other sources say Mr. Nassir's ELF commands greater respect and loyalty on the grass-roots level than the EPLF. The EPLF, however, has benefited from better guerrilla organization and supply links.

The EPLF maintains that the ELF has been negotiating secretly with the Ethiopians; Ahmed Nassir denies the allegation.

A recent rapprochement between Addis Ababa and Khartoum has caused difficulties for both rebel operations. In March 1980 Sudan and Ethiopia agreed to work for a ''speedy elimination'' of all problems between them. These include withdrawing support for opposition groups that have sought refuge in each other's country.

Sudan closed down the guerrillas' political offices in Khartoum. It ruled that Eritrean refugees can travel in Sudan only with a government permit. It also disarmed some of the guerrillas, but it is not easy to keep them without supplies.

Sudan is holding the Eritreans as a trump card in its relations with Ethiopia. Sudan constantly worries about Libyan subversion and was not happy when Ethiopia signed a cooperative pact with South Yemen and Libya last August.

Addis officials told Sudan President Nimiery that Ethiopia entered into the pact for financial gain, but Mr. Nimiery is suspicious about these motives.

Thus while Sudan has pledged to curb Eritrean activities in Sudan, tacitly it appears to allow such activities to continue. Arms destined for Eritrea filter through Port Sudan, although there may not be much the government could do about this even if it wanted to.

It is difficult to obtain firsthand information to assess the claims and counterclaims of the government and the rebels. Fighting seems to be on a lesser scale than in the late '70s, but it shows no sign of ending.

In many ways the world seems to have forgotten the Eritrean resistance struggle, now Africa's longest war. Without Soviet and Cuban military support, the Ethiopians would probably find themselves in a position like that of 1978.

Militarily, the liberation movements seem unlikely to defeat the Ethiopians without a massive political upheaval. Such an upheaval is unlikely. But they struggle on. Their best hope appears to be gradual change.