In the dark of the night, three giant color portraits of Marx, Lenin and Engels stand bathed in flood lights behind Revolution Square at the city's center, bearing stark witness to the hurricane of change that has swept over this ancient Christian land that once ranked as America's closest ally in black Africa.

Beset by civil war, a separattist movement in the north, an invasion by regular and guerrilla Somali forces in the southeast, and intense internal strife. Ethiopia has just celebrated the third anniversary of its revolution more than ever a house dividen against itself.

It was three years ago Sept. 12 that an obscure group of junior army officers deposed the world-renowned Emperor Haile Selassie and abolished the 2,000-year-old Ethiopian monarchy with supreme skill and without a drop of blood.

For a short time, the revolution remained bloodless. But first the execution of 60 high officials of the old regime and then radical rural and urban land reforms in 1975 set landlord against peasant and Ethiopian against Ethiopian with increasing bloody revenge.

After tacking far to the left this spring to become Africa's latest Soviet-backed Marxist state, the military government ruling this besieged East African nation is now caught in strong cross currents of marxism and nationalism, the first stirred up by the revolution and the latter by the war with Somalia.

At this point, it is impossible to predict the outcome of most of the conflict tearing at Ethiopia's new political fabric: north will finally break away to establish a new state; whether Somalia will succeed in annexing the disputed Ogaden region: whether the "Marxist" or "Nationalist" faction will prevail in the revolution or whether even the ruling Provisional Military Government will survive.

But right now, Ethiopia appears dangerously close to losing both Eritrea and the Ogaden, losses that would reduce its land mass by more than one-third and have untold consequences for the present military government and the rest of the country.

The government has launched an Ethiopian-style "people's war," mobilizing 150,000 to 200,000 peasant soldiers in a desperate last bid to hold the nation together.

But it remains uncertain that such a war can be waged effectively either in the semi-desert Ogaden or the wild mountainous terrain of Eritrea, where will-armed and foreign-backed Somali and Eritrean nationalists are now largely in control and just as determined to win.

Meanwhile, the fate of Ethiopia has passed in large part into the hands of the Soviet Union, the big power that first poured massive quantities of arms into Somalia to make possible the Somali invasion of the Ogaden and is now doing the same in Ethiopia to frustrate the Somali objective.

The United States, the main arms supplies to Ehtiopia for the past 24 years, is now conveniently in a position to forget its past commitment to the defense of Ethiopia's territorial integrity and to avoid another direct, or indirect, confrontation with the Soviet Union in black Africa. Last April the Ethiopian military government unilaterally broke all its military ties to Washington and canceled the 25-year American-Ethopian defense pact.

For once, U.S. policy makers can sit back and watch, no doubt with considerable pleasure, the Soviets squirm in a predicament of their own making and from which they seem unlikely to emerge the trusted ally of either Ethiopia or Somalia.

The twists and turns of the Ethiopian revolution have produced some strange bedfellows among its foreign backers, who include Libya, Israel, South Korea, and West Germany together with China, East Germany, North Korea and the Soviet Union.

The Libyans are reportedly providing money, arms and diplomatic support; the Israelis a score or so of military advisers, some security support and spare parts for American-made weapons; South Korea uniforms for the army and peasant militia and West Germany advisers and material for the police force.

The Cubans, on their way to numbering about 400 altogether, are sending mostly doctors but also 50 to 100 military advisers who among other things were reportedly involved in organizing the successful defense of the city of Dire Dawa, attacked by the Somalis Aug. 16-17. In addition some reports say that 15 Cuban doctors and advisers were injured in fighting around the fallen town of Jigjiga recently.

There are conflicting reports regarding the effectiveness of the Cuban military team. Some suggest the Cubans have not gone over well with the Ehtiopian military, which regards itself with some reason as far more experienced in both conventional and anti-guerrilla warfare than the Cubans. But by nearly all accounts the Cuban doctors are badly needed and much appreciated.

Meanwhile, East Germany and the Soviet Union are providing the bulk of the arms and munitions. Soviet military personnel are a common enough sight these days in the hotels of the capitals, though no Western embassy seems to know how many are serving now.

But there are probably still fewer Soviets here than in Somalia where they once numbered around 2,500 and were assigned down to the company level of the Somali army before the current Somali-Ethiopian war broke out.

The Ethiopian military government has done an extraordinary job of juggling its new array of often incompatible foreign allies and of keeping the assistance of the more controversial ones discreet. Libyan assistance is seldom mentioned, the Israelis are seldom spotted in public, the South Koreans are rarely seen and the Cuban military role is kept a total secret.

When asked about the Israeli presence in the country, Ethopian officials do not really deny it, but dismiss the reports as an Arab "pretext" for aiding this country's enemies. As for Cuban military assistance, the Ethiopian answer is that there is no shortage of manpower to fight the wars in the Ogaden and Eritrea and that "no foreign troops" are involved - all of which is probably literally true.

Despite strong Soviet and Cuban influence now on the military government, it is still unclear what ideological orientation the revolution will ultimately take.

After four months absence from Ethiopia, perhaps my strongest impression on returning is the growing force of the Marxists within the revolution. Their impact can be seen in the numerous red flags with hammer and sickle to be seen at parades and around town, the pictures of Marx and Lenin that appear everywhere and the sound of "International" sung on the state radio and often by small groups in public.

Thanks to an extremely acive ideological school where only Marxist-Lenist doctrine is instilled in one or three months courses, over 5,000 Ethiopians have now been indoctrinated in the thought and methods of the Soviet revolution and to a lesser extent the Chinese one. Hundereds of other civil servants, students, professors and army officers have been sent to Eastern European countries for similar "re-education" in socialist ideology.

There are now five semi-official Marxist-Leninist groups struggling to dominate the political party that the military government has promised to establish to lead the revolution.

The squabbling among them over the fine points of Marxism-Leninism as they should be applied to Ethiopia - and above all over how to deal with the military - has led to intense political strife among civilian leftists. Together with the illegal opposition Ethiopian People's Revolutionary Party, two of these Marxist factions now operate assassin squads that are busy wiping out each other's leaders and followers.

In the past nine months, 200 officials of the neighborhood dwellers' associations, the local organs of government, in Addis Ababa alone have been assassinated by one or another Marxist faction and another 200 seriously injured, according to city officials. The week following the Sept. 12 celebrations of the revolution, five more were reported killed in broad daylight and the sound of gunfire at night suggested the toll may have been higher.

Previously, the state controlled media gave considerable publicity to these assassinations, blaming them all on the clandestine apposition group. But now little or no mention is made, apparently because no one is sure whether it is a pro or anti-military faction responsible for them.

Still, compared to last spring, Addis Ababa is a much quieter and more orderly capital.

The bitter struggle for power among civilian Marxist groups has inevitably had its effect on the ruling military council which has come to distrust thoroughly even its own civilian supporters.

In fact. the main faction heretofore backing the military, the All-Ethiopian Socialist Movement, has joined the ranks of the opposition now and 200 of its top officials have either gone underground, fled the country, been killed or captured in the past six weeks.

Among those who fled but were later captured was Haile Fida, the Marxist ideologue who once headed the powerful Provisional Office for Mass Organizational Affairs, the country's pre-party political organization.

The fall from grace of the All-Ethiopian Socialist Movement and the rise to power of the military's own faction known as the Revoluntionary Flame is partly responsible for the recent resurgence of the "nationalist" current in the revolution and also for the military council's decision to try to repair its relations with the United States to strike a more nonaligned posture.

But these new developments are also partially explained by the war situation which has now become the all consuming concern of the military government. It has been appealing primarily to the patriotic spirit of every Ethiopian in an effort to rally the nation against the invading Somalis and separatist Eritreans realizing full well that nationalism rather than Marxism is the only force capable of unifying Ethiopians in the present national crisis.

The civilian Marxist extremists condemn the government's rallying cry of "revoluntionary motherland or death" "reactionary." They regard the fate of the revolution as still more important than national unity.

Where all this internal zig-ziging and brickering between the military and the civilians is taking the country and the revolution is anybody's guess. But Ethiopia at a time of extreme national crisis seems more than ever a house divided against itself and as entangled in a revilutionary process as powerful as the Soviet andChinese ones that saw years of confusion and civil war before a new order emerged.