The war breaking out between Ethiopia and Somalia over the disputed Ogaden region has been in the making for fully 18 months and has every likelihood of escalating into a full-scale confrontation, involving the big powers, at least indirectly.

The present Ethiopian strategy is aimed precisely at this, Somalia diplomatic sources here contend. They are convinced that the military government in Addis Ababa is seeking to internationalize the conflict to force Washington and Moscow to intervene to halt the fighting and then demand the withdrawal of the two countries' regular and irregular armed forces from the region.

This would give the Ethiopian government the time it desperately needs to reinforce its thinly stretched army in the Ogaden, while leaving the disputed territory still in its hands, according to Somali thinking.

The Somalis believe that Ethiopia may soon attempt an incursion into Somalia to achieve its objective of widening the conflict and also to give it a chip to bargain with later, if and when the two neighboring Marxist governments should negotiate.

Somali insurgents fighting in the Ogaden with the backing of the regular Somali army are likely to counter an incursion by accelerating their efforts to cut off land and air routes of the Ethiopian army into the disputed region and thus prevent a buildup of its forces there.

Ethiopia is already trying to transport regular army units plus elements of its new 100,000-man "peasant army" to the Ogaden, according to diplomatic and press reports.

This Somali thinking explains why the insurgents have already cut the railroads leading from Addis Ababa to Dire Dawa, the largest town in the disputed region with a good international airport and the main staging area for the Ethiopian army in the region together with Harrar and Jigjiga.

It also is the reason the insurgents are seeking to capture Gode in the far southeast, the only town deep in the Ogaden with a macadam airstrip capable of taking both jets and transport planes.

There have been conflicting reports over whether the insurgent group, the Western Somalia Liberation Front, has succeeded in taking Gode, where fighting has been going on for weeks.

If the Somali insurgents have captured Gode and also are able to isolate the three key towns of Dire Dawa, Jigjiga and Harrar then the Ethiopian army will have an extremely difficult time mobilizing reinforcements for a push into Somalia or a counteroffensive against the insurgents.

The insurgents already claim to control two-thirds of the 100,000-square-mile semi-desert region and to have captured about a dozen towns.

Ironically, it was the Ethiopian military government that predicted long ago that Somalia was preparing to go to war against Ethiopia to fulfill its 17-year-old irredentist claim to both Ogaden and the new Republic of Djibouti.

Ethiopia has apparently been caught off guard, however, having depleted one division stationed in the Ogaden to meet growing military threats in the far north and northwest from the Eritrean secessionist movements and the anti-Marxist Ethiopian Democratic Union.

The situation in Eritrea is just as critical for the central government as it is in the Ogaden.

In January, 1976, Ethiopia sent a memorandum entitled "War Clouds in the Horn of Africa" to a number of African leaders spelling out in great details what it alleged was the Somali "war plan" for annexing Ogaden and Djibouti.

The 39-page document a copy of which The Washington Post obtained shortly after its publication, told of a sharp increase in the infiltration rate of Somalt insurgents into Ethiopia's southeastern provinces of Harrarghe, Bale and Sidamo beginning in November 1975.

It alleged that Somalia's goal was to force Ethiopia to disperse its troop throughout a large area to facilitate a direct attack by Somali regulars into the Ogaden.

Somalia, the Ethiopian brief asserted, had taken a decision in the summer of 1975 to set in motion a "war of subversion" in preparation for a "full-scale war" to be launched later. It charged that the Somalis in effect "have made a decision to go to war against Ethiopia immediately."

As regards the "war of subversion," the Ethiopian analysis seems to have proven correct. From early 1976 onward, hundreds of Somali guerrillas began crossing into southeast Ethiopia.

By early this spring, the front had at least several thousands extremely well-trained, well-armed guerrillas in the disputed territory. Even then, they were confident enough to attack Ethiopian army convoys, police stations and army bases in daylight.

Activities of the Ethiopian Drought Relief and Rehabilitation Commission throughout the Ogaden virtually ceased, and all foreigners had to be evacuated.

In late May, the front leader, Abdulahi Hassan Mohamud in an interview with The Washington Post, predicted "total liberation" of the region by the end of this year. He gave detailed accounts of several major insurgents victories over regular Ethiopian army units. The interview was held in the Somali capital of Mogadishu, where the front has its headquarters.

Ethiopia maintains that the front is merely an extension of the regular Somali army and alleged in the 1976 memo that it had already captured "regular Somali army men and officers" leading guerrill operations in the Ogaden.

On Thursday, the Somali government admitted for the first time that its Soviet-provided Mig jets had tangled with Ethiopia's American-built F-5Es over Ethiopian territory but was still denying that its troop were involved in the fighting.

On Wednesday, the Somali ambassador in Paris, Mohammed Samantar, said in an interview that two Ethiopian F-5Es and two Somali Mig-17s had been shot down in a dogfight over the northern Somali city of Hargesa. He charged that the Ethiopian air force attempted to bomb the city but said that aircraft were driven off before they reached it.

The Somalis expect any Ethiopian incursion to aim at Hargesa in drive to cut through the northwestern part of Somalia and sever the north from the south.

The seeds of the current Somali-Ethiopian conflict were sown in 1960 when British and Italian Somaliland were united to form present-day Somalia, but Ethiopia refused to give up territory that Emperor Menelik had conquered in the late 19th century or that British had ceded to it in 1954.

Somalia laid claim to its "lost territories" that include not only about a third of the land mass of Ethiopia, but also Djibouti and the Northern Frontier district of Kenya. It bases its claim on the presence of Somali-speaking people in all three areas, although about 40 per cent of the population of Djibouti is composed of Afars who do not speak Somali.

No fire burns brighter inside Somalia's seven-year old socialist revolution than that of nationalism. The country's flag have a five-pointed star, three of whose points stand for the "lost territories." Under the constitution the government is pledged to work for the reunification of the estimated 9 million Somali-speaking people in northeast Africa.

Ethiopia has the charter of the Organization of African Unity on its side. It pledges all African states to respect colonial borders as they were in 1963 at the founding of the OAU regardless of their arbitrary nature. In the diplomatic struggle inside the organization, Ethiopia has generally enjoyed far wider support than Somalia.

Somalia has been preparing for the struggle over the Ogaden since its army was totally routed by the much bigger and better American armed Ethiopian forces in the brief border war of 1964. Only U.S. intervention prevented the Ethiopians from marching to the Somali coast and cutting the country in two.

Shortly after the army came to power in Somalia in 1970 under President Mohamed Siad Barre, the government launched a socialist revolution and signed a treaty of friendship with the Soviet Union, the first black African state to do so.

Perhaps the main fruit of that treaty for Somalia was massive military assistance that has turned the Somali army into one of black Africa's best-equipped and best-trained.

Somalia today has far more aircraft, tanks and armored personnel carriers than Ethiopia. Somalia 22,000-man regular army, still less than half the size of that of Ethiopia is highly mobile.

The Somalians are also far better organized and disciplined but war-weary Ethiopian army, which has been fighting non-stop for the past three years on multiple fronts against opponents of Ethiopia's ruling Military Council.

The Somali army, however, still has some 4,000 Soviet advisers serving down to the company level to keep it functioning. Were they to be withdrawn, it is not clear what would happen.

Meanwhile, the Soviet Union recently rushed about 150 tanks and armored personnel carriers to Ethiopia following the decision in December to help Maj. Mengistu Haile Mariam, the new pro-Soviet chairman of the Military Council, to overcome his and the revolution's enemies.

Ethiopia has also just organized a peasant army of 100,000 to bolster its regular army, which now probably numbers around 60,000.