On the face of things President Mohamed Siad Barre of Somalia should be a worried - even desperate - man now that he has expelled the once pervasive Soviet military presence here at time when he faces more fighting with the Ethiopians.

Initially it was thought that Siad Barre would face a crucial period in which he could even be overthrown from within, especially after the United States maintained its neutral stance even after the Soviets were expelled.

Now, there is no question about his people's wholehearted support for his decision to expel the Soviets. If anything, he lagged well behind his ultra National 1st public opinion, which for nationalist public opinion which for his reluctance to break with Moscow after it switched sides and began helping arch enemy Ethiopia.

Still, the dangers facing this rockstrewn nation of less than 4 million are real indeed, even if Siad Barre's claim that 20,000 Cubans are in Ethiopia is grossly exaggerated.

By his own admission, his erstwhile Soviet allies - and their Cuban and South Yemeni surrogates - are providing Ethiopia with a wealth of weaponry and expertise to try to smash Somali forces fighting inside Ethiopia's disputed ogaden region.

With the exception of some Italian light and anti-aircraft guns, the Somalis have apparently failed so far in their public and private efforts to have the West - or its regional allies in the Middle East - provide massive heavy weapons to help deflect the feared Ethiopian onslaught.

Siad Barre told a news conference only Wednesday that American Ambassador Joh Loughran had returned from three weeks in Washington with "no good new."

Somali officials conceded privately that the West had paid no visible price for having the Soviets deprived of major naval, air and communications facilities along the strategic approaches to the Bob el Mandeb Straits controlling the entrance to the Red Sea. Siad Baree told reporters he had received "not any assurances at all" before ordering the expulsion Nov. 13.

Specialists are convinced, however, that Siad Barre's professed disappointment with the unwillingness of the United States to rush to his rescue - in the name of defending tis own interests and those of "friends" stretching from Iran to Kenya - is in part feigned.

He is credited with understanding that a post-Vietnam United States is in no mood to fill the "vacuum" left as the Soviets exit. Those days of automatic cold war reaction appear gone, at least for the foreseeable future.

Meanwhile, the Somalis' seemingly unflappable self-assurance is understandable on diplomatic, military, political and even psychological grounds.

Sian Barre has proven himself a master poker player, capable of sensing his adversaries' weaknesses and exploiting them; of making his own mistakes, but correcting them.

Perhaps more than any other leader of an independent African nation, Siad Barre commands absolute support from his highly disciplined people on one issue - the demand for the eventual reunification of all Somalis living in Ogaden, in Kenya's northern frontier district and in the now independent, former French possession of Djibouti.

"We can admit the separation of our Somali brothers living elsewhere," a Somali official said, "but we will never renounce our dream of uniting them in the nation" and thus correcting the vagaries of Italian, French, British and Ethiopian imperialism.

Somali motivated and grit - and poor Ethiopian army morale - help explain why the Ethiopians' Soviet provided weaponry has not yet driven out the outmanned and outgunned Somalis.

Those considerations could also account for still vague reports that Somalis are fighting inside Harrar, the Ethiopian city whose capture would open the way for the Somalis to take the area's only concrete airstrip at Aire Dawn.

Also aiding the Somalis has been the success of nationalist guerrillas in Eritrea, Ethiopia's window on the Red Sea. After 16 years of fighting for independence, they have all but taken over the province despite a serious split in their own ranks, the split has not prevented coordination with the Somalis, however.

In the Ogaden itself, the Somalis can count on the active support of the indigenous Somali's speaking population, fed up with it denounced as a century of Ethiopian "colonial" rule.

Demoralized by a seried of recent major defeats both in Eritrea and against the Somalis, the Ethiopian armed forces and peasant militia have yet to prove themselves capable of fighting the kind of sustained war required to push the Somalis out of Ogaden.

The Ethiopians and their foreign advisers are credited with two possible strategies.

One calls for a classic offensive to recapture the heavily mined Ogaden lowlands, but this would first require dislodging the Somalis from their easily defended positions in the strategic Kara-Marda, pass in the mountains above Jijiga.

Although the Ethiopians have mastery of the an and are heavily armed, observers say any such campaign could well bleed Ethiopians badly without exhausting the Somalis, who are on friendly ground and much closer to their supply bases.

Siad Barre himself insists that the Soviets really intend to have the Ethiopians cut across northern Somalia - after taking the Kara-Marda pass - and capture Hargeisa and Berbera, the recently evacuated Soviet naval and air base on the Gulf of Aden. That may be basically for international consumption.

Siad Barre knows however that any obvious Soviet aggression against Somalia proper would further darken the Soviet and Cuban image in Africa so far.

The West is in no mood to provide heavy weapons that Somalia wants to help capture harrar and Dire Dawa. That would amount to countenancing Somalia's land claims and fly in the face of the respected principle of recognizing African colonial frontiers no matter how arbitrary.

If Somalia were threatened by a Soviet backed invasion however the West would be hard pressed not to provide arms.

A high Somali official summed up the situation by saying that "The West is going along with Somalia but silently."

He thus implicity recognized that any major overt Western aid to Somalia at this juncture would provide the perfect pretext for the Soviets to justify their own military presence in the Horn of Africa.

Yet another pro-Somali facor is the moral credit procured by its coorperation last month in authorizing the West German government to rescue a hijacked Lufthansa jets and its passengers from terrorists at Mogadishu airport.

Compared to the continuing bloodletting in and out of Ethiopian government ranks, Somalia is emerging as a country which at very least has earned it right to expect help in an emergency.

Whether such an emergency - especially a military one - well develop remains to be seen.