Eritrea's rival liberation movements are riding the crest of the most impressive military victories in their nearly 17-year-old fight for independence from Ethiopia.

But their mood is far from euphoric, whatever the public posturing, and even the fierce fighting in the Ogaden regions, where Somali irregulars are lying down ethiopian troops, is viewed as a mixed blessing.

Spurred into the offensive before the increasingly rapid tempo of Soviet arms deliveries to Ethiopia is felt. The Eritreans are also bracing for the imminent onslaught of what they fear may be as many as 45,000 Ethiopian soldeirs and peasant militiamen.

Even as the pace of their battlefield victories quickens, the liberation movements are increasingly estranged to the point, that their leaders privately speak of the possibility of an Angola-style civil war - "or worse" - to settle their rival claims.

Reflecting on the increasing out spoken backbiting and innuendo afflicting the Eitrean nationalists, one leader said "Our prime problems is not Ethiopia, but our divisions."

The Eritreans' rivalry has reached the point where independence sources confirmed reports of a series of mutinies and arrests within the ranks of the original - and still largest - nationalist group, the Eritrean Liberation Front.

Its leadership, the sources said, recently took undisclosed but reportedly stern measures after an ambush in which dissident ELF troops killed veteran commander Ramadan Abdel Kadr and another member of the Front's ruling Revolutionary Council.

The Eritreans know full well that their best bet for achieving independence soon lies in quick unification, but they are paralyzed at what they concede is a crucial time on their struggle.

Some Eritreans are already beginning to regret the final phase of the generation-long U.S. arms involvement with Ethiopia, in which deliveries were cut back sharply. They wonder if the Soviet presence may succeed in frustrating their goal of independence.

Furthermore, they are worried by changing attitudes in Sudan, where last winter's all-out support for total independence appears to have given way to a preference for local autonomy - which is anathema to all the Eritrean groups. Such prudence is apparently dictated by the military collapse of the rightist Ethiopian Democratic Union in June and the belief that Soviet military aid may prove sufficient to keep Ethiopia from breaking up, if not to present continued trouble in Eritrea and the Ogaden region.

Diplomats noted signs that Sudan now favors some kind of rapprochement with Ethiopia - and between Ethiopia and Eritrea.

"All of us have a vested interest in compromise," a high-ranking Sudanese official said, recalling the granting of local autonomy that ended Sudan's long civil war only five years ago. "Yes, everyone in the region except the Eritreans." [Diplomatic sources in Paris, however, said that during Sudanese President Jaafar Nimeri's visit to Riyadh this week the Saudis agreed to provide an injection of badly needed cash for his overextended economy in return for more resolute opposition to Ethiopia.]

Once again the Eritreans appear about to be frustrated by their unfortunate geographical position - 600 miles of strategic coastline near the Red Sea's narrow entrance - which has left them without major foreign friends, but with now diametrically changing enemies.

Officials of the more radical and disciplined Eritrean Popular Liberation Front discount suggestions that they have sought to subvert ELF ranks.

They insist that the ELF's "internal contradictions" are accelerating its "disintegration" and predict that it "will not be long" before most ELF forces come over to their side.

In turn, Popular Liberation Front is said by its rivals to have so much internal opposition that it arrested some 700 of its own dissidents.

Since the Popular Front broke away from the parent organization in 1979 - and especially as a legacy of the bloody Ethiopian civil war between 1972 and 1974 - such talk is hardly surprising despite sporadic but inconclusive efforts to unify the Eritrean liberated movements.

Under public pressure for unity, the rival revolutionaries have managed in recent years to moderate their criticism of each other and make proforma statements favoring unity - albeit on mutually exclusively terms.

Symptomatic of the mutual suspicions are doubts cast on the Popular Front's victory at Karen - the most importance event of this long and often forgotten war - by the ELf and Osman Saleh Sabbe. Sabbe's small organization, now affliated with the ELF, was expelled by the Popular Front three years ago and is believed to field no more than 4,000 troops. The ELF is thought to have about 20,000 men under arms and popular Front is credited with almost that number.

Perched atop a mountain, the fortress at Keren, which took the British three months to capture from the Italians in 1941, felt July 8 after no more than five days of fighting.

The Popular Front was surprised and delighted, but it remains oddly unable to provide details of the operation. Colette Braeckman, a Belgian journalist working for LeSoir, reported seeing hundres of corpses and evidence of bitter fighting when she entered Keren three days later.

The ELF, which intercepted and killed 300 of the 500 Ethiopians who escaped from Keren, reported that one prisoner said, "We could have held out for two years without receiving additional food, water, ammunition or medicine."

The prisoner was also quoted as saying that the fortress commander had given his troops - variously estimated at anywhere from 4,000 to 8,000 men - the choice of fighting, surrendering or making a run through Eritrean-held territory to the equally surrounded Ethiopia garrison at Agordat to the south.

The Keren garrison - the second largest in Eritrea after the 15,000 men believed to be stationed in Asmara - the capital had long suffered from declining morale. In February a 31-men delegation was sent to Addis Ababa to argue for peace negotiations. It was told to hang on for three months because reinforcements were being trained to recapture the secessionist province.

Further demoralization was caused by survivors who straggled back to Keren after an ill-fated relief column was cut to pieces last winter before reaching its objective - the surrounded Ethiopian garrison at Nakfa which eventually fell in March.

The Keren garrison was so depressed that it hauled down the Ethiopian colors and flew the white flag for 21 days.

Observers theorized that effective Popular Front psychological warfare and a tendency toward local accommodation culminated in the apparently half-hearted defense and relatively easy capture of Keren.

ELF officials suspect that as many as 8,000 troops manned the garrison, which their military experts considered of much greater military importance than the capital city itself. That figure is twice the 4,000 men reported by the Popular Front.

The discrepancy helps explain why the ELF suspects that the Popular Front played down the size of the garrison to avoid honoring an agreement to split all arms and ammunition captured in that theater of operations.

Both movements depend on weapons and ammunition captured from the Ethiopians. ELF sources said that in addition to tanks, armored cars and heavy artillery, as many as 10,000 crew-served and individual weapons - including recently delivered Soviet arms - were captured in Keren. That would represent the war's biggest booty for the Eritreans.

So bitter are the Popular Front's rivals that some sources are not beyond suggesting that it made a direct deal with the Dergue, the Marxist military government that holds tenous power in Addis Ababa.

Observers find such charges far-fetched, but Ehtiopian government propaganda has traditionally been more tolerant of the "progressive Popular Front than of its "reactionary" rivals.

The current major ELF-Sabbe operation against the 6,000-man Ethiopian garrison in Agordat is thought to have been dictated as much by a desire to equal the Popular Front victory at Keren as by military necessity, since the Ethiopians are cut off there in any case.

In contrast to the relative walkover in Keren, ELF spokesmen report hand-to-hand fighting and five-times a day air raids by six planes against its forces, which are now said to be within 20 yards of the Ethiopians' underground positions.

Popular Front spokesmen insist that "Because of our victories we have made a breakthrough and are recognized as a military and political power not just in Eritrea, but in the Horn of Africa as well, where we have responsibilities as a strong, progressive military power."

Observers are less impressed by the Popular Front showing abroad than in its growing prowess in the field.

Its proud insisitence on self-reliance is seen as the rationalization of its own political - and financial - isolation in the Horn of Africa and the Red Sea area, where once-radical governments in North Yemen, Sudan and even staunch ally Somalia are rapidly turning toward the petrodollars offered by conservative Arab governments led by Saudi Arabia.

The ELF makes no such claims. Its leadership is frankly worried by the immediate threat of the new peasant march that is expected to invade Eritrea sometime this month. The Eritreans, especially the ELF, easily put the first such "red march" to flight just inside Eritrea in June, 1976, but that contingent was notoriously ill-trained, ill-armed and ill-led.

Their concern is heightened by the knowledge that the invasion path first crossed ELF-held territory Ehtiopia has marshalled its invasion forces at three important road junctions just inside Ethiopia proper.

To meet this border threat, the ELF - and its allies loyal to Sabbe - fear that they must pull troops away from positions farther inside Eritrea. Perhaps inevitably, this redeployment is seen as favoring the Popular Front and, among the more suspicious, is viewed as implicit proof of collusion between the Popular Front and the Ethiopian enemy.

The Popular Front has sought to allay such suspicions by refusing to respond to Ethiopian overtures for separate negotiations excluding the ELF.

To this end, the Popular Front recently handed over to the ELF an Ethiopian letter suggesting just such talks.

The Ethiopians have an easy out when it comes to declining negotiations with Eriteans, since there are three movements to deal with and each is likely to brand the first to agree to peace talks a traitor.