The streets of the capital of Marxist Ethiopia are still lined with colored lights put up nine years ago to commemorate the 80th birthday of the late emperor, Haile Selassie I.

But the lights spelling out "HSI" have been replaced by a lighted hammer and sickle.

In the seven years since a wrenching revolution ended an autocratic monarchy claiming to trace its roots back 3,000 years to the biblical King Solomon, this key nation in the Horn of Africa has undergone convulsive changes. Marxism has replaced feudal capitalism, and land barons are a thing of the past. An illiterate populace is flocking to schools. Ethiopia has shifted alliances from West to East.

Yet in some ways, this major African revolution has done little to change the style of rule perpetuated by the emperor during more than half a century of one-man authority. The country's leader, Lt. Col. Mengistu Haile Mariam, has turned Ethiopia upside down poliically while retaining many of the trappings of the monarchy.

Although a number of consultative bodies have been established, there is little question that Mengistu is the single authority in the country. He even uses the same throne as the emperor at festive occasions.

Just like Haile Selassie -king of kings, elect of God, conquering lion of the tribe of Judah -Mengistu uses three titles, albeit somewhat more prosaic, after his name. He is chairman of the Provisional Military Administrative Council and the Commission for Organizing the Party of the Working People, the military and predominantly civilian institutions running the country. And he is commanderin-chief of the revolutionary Army, the means through which he came to power.

An American-educated Ethiopian official, who did not hide his opposition to the government when talking privately, said with a smile: "We have traded the trinity of the Ethiopian Orthodox Church [the former state religion] for a new bearded trinity -Marx, Engels and Lenin."

But as Marxist rhetoric has replaced obeisance to the Solomonic dynasty, the military has remained the key to power. Both governments have used the powers of the state freely to suppress opposition, one in the name of the king, the other in the guise of a dictatorship of the proletariat.

Just as in the past, "the only way to oppose is to revolt," a longtime foreign resident said. Acknowledging this, an Ethiopian official said, "In Africa, there's no opposition bench. People come to power through violence, usually."

Although political tensions have eased considerably in the last several years as the government has become entrenched and people have become more willing to talk, fear and repression are still probably greater than under the old government.

"These Marxist rulers have no sense of humor. You can't fool around and sneak things into the press like before," an official said during lunch while nervously pausing to observe everyone who entered the restaurant.

Estimates of the number of political prisoners range from 10,000 to 40,000. Almost all are opponents of the revolutionary government.

Many are "radicals," dissatisfied with military rule and the pace of the leftward trend, but about 200 are officials from the old government, including about a dozen members of the emperor's family, headed by his daughter Princess Tenagnework and several granddaughters.

People still vividly remember the "Red Terror" days of 1977-78, when more than 5,000 Ethiopians were killed in six months of political violence. It was a routine occurrence to see dead bodies on the streets of Addis Ababa.

A longtime British adviser who has served both governments and is sympathetic with the Mengistu government sought to put the killings in perspective: "Ethiopia is compressing the history of Britain from the Norman conquest to the Industrial Revolution into one generation. It is turning society upside down. In that context the number of deaths is minuscule."

Even opponents of the government acknowledge that it has made significant progress in a variety of social fields when movement under the emperor came at a snail's pace.

The literacy rate has gone from one of the lowest in the world, 7 percent, to more than 35 percent, and school attendance has more than doubled. Emphasis has been placed on rural development. About 43 percent of the population now is estimated to have access to health services, as opposed to 15 percent before the revolution.

After years of lip service to land reform under the emperor, peasants now own the land they till and no longer have to pay half or more of their crop to a landlord, often absent, for rent. There is evidence that they are much better fed.

The accomplishments are all the more significant, because, as one Western diplomat said, "You can forget the first four years of the revolution," -the chaos caused by the political upheaval, a war against Somalia and guerrilla struggles in various parts of the country.

"They have gone very, very far in dragging the country up from the Middle Ages," said Hans Dall, the representative of the U.N. Food and Agriculture Organization.

There is still a long way to go, however, as is evidenced by the growing complaints about the country's economic difficulties.

Marxist organizational methods have played a key role in many of the government's achievements.

For most of Ethiopia's history, the emperor was the government and he appointed officials at regional levels. There was no tradition of local government, elected or appointed.

All that has changed in revolutionary Ethiopia, where each major city or town has a system of elected representation for each district, called kebelles, of about 5,000 population. Each kebelle is responsible for its own security, has certain judicial powers, runs cooperative stores and has other responsibilities.

During the "Red Terror," kebelles got a bad name since they imprisoned thousands of persons in the capital and were also responsible for killings.

The kebelles have brought governmental organization to the local level and, therefore, are a means of exerting control. On a recent Sunday, for example, all kebelles in Addis Ababa held compulsory seminars dwelling on the evils of "nontraditional" religions, meaning everything but the Orthodox Church and the Moslem faith.

By introducing self-administration for the first time, however, the government has opened a crack of democratic practice unknown in imperial Ethiopia. Although the government put up a list of accepted candidates in last summer's kebelle elections, other nominations were allowed, and a number of the nongovernment candidates were elected.

In the countryside, peasants' organizations take the place of kebelles , and they have been instrumental in implementing land reform. There are reports that sometimes they have been used to help pressure peasants into joining cooperatives, but government officials deny this.

The 25,000 peasant organizations have a membership of 7 million. "Under any standard it is a fantastic feat of organization," Dall said. In addition, the government has established thousands of women's and youth organizations nationwide.

Despite the elements of control, these organizational structures have given the people some voice in their affairs for the first time.

Numerous officials and diplomats noted that this has resulted in Ethiopians no longer adopting a subservient attitutde toward their bosses.

"No Ethiopian says getouche [master] any more," one official said. Except for the ubiquitous beggars, that is probably true.

Officials say it is hard to reverse centuries of tradition among Ethiopians who invariably looked to the emperor to solve their problems. Officials say efforts are now concentrated on ideological training to get the people to demand changes, following Marxist guidelines.

A case in point is the presence in the Red Sea port of Massawa of possibly the only remaining statue of Haile Selassie in the country. In Addis Ababa, all statues of the royal family have been removed. Many have been taken to the museum grounds, where the heads are covered with buckets.

At the entrance to Massawa's port, however, a statue of Haile Selassie on horseback and pointing toward the sea is still standing. The entire edifice has been covered wiih straw matting, making the statue look something like a scarecrow.

"We are waiting for the people to have their consciousness raised enough to demand to have the statue removed," an Eritrean regional official said.

Ironically, although Haile Selassie has become a nonperson with his name removed from almost all sites, his predecessors' names are still retained on public places.

It is all the more ironic, since nothing in the country is named after Mengistu, although his picture is seen everywhere.

His reported opposition to the personality cult encouraged by the emperor is striking in a country where one-man rule has been, and still is, the order of the day.

Several analysts say that Mengistu has maintained some of the trappings of the monarchy simply because that is what his people expect. Part of the aura is that of a man of mystery.

The Ministry of Information has no official biography of Mengistu and even his age is a subject of controversy. He is variously reported as being 39, 41 or 44 years old and is believed to have three children.

There is a dispute about whether he is an Amhara, the minority tribe that has long ruled Ethiopia, or partly Oromo, Ethiopia's largest tribe.

Mengistu does not live in Jubilee Palace, the emperor's finest home. Instead he lives in what is described as a relatively modest house on the grounds of the ramshackle Gibbi Palace.

Many political prisoners are kept on the same grounds.