Ethiopian officials backed by armed soldiers today took over the headquarters of the country's major Protestant denomination in a move that could have far-reaching impact on the Marxist government's tentative efforts to improve relations with the West.

The seizure is likely to revive charges abroad that the pro-Soviet government is persecuting Christians despite Ethiopia's history of being a bastion of Christianity in Africa for 16 centuries.

The Ethiopian Evangelical Church, whose building was seized, unites the various Scandinavian and German Lutheran denominations and groups most of the half-million Protestants in the country. About 40 percent of Ethiopia's 31 million people are members of the Ethiopian Orthodox church and about 45 percent are Moslems.

During the weekend the Swedish government sent a message to the Ethiopian Foreign Ministry demanding reconsideration of the decision, citing the impact it could have on Sweden's $20 million annual aid to Ethiopia, the largest amount of bilateral assistance this country receives.

It is far from clear, however, that the takeover of the eight-story office building of the church is simply an antireligious move. Some Western diplomats and church leaders think that the government's need for office space and the country's tribal problems could be more significant reasons for the action.

The government of Lt. Col. Mengistu Haile Mariam has given no reason, and officials have declined repeated requests for comment.

"You cannot ask questions" about the seizure of the church property, an official said.

Although some churches in the countryside were closed earlier this year, the current move is limited to the headquarters of the church, known as Mehane Yesus in Ethiopia's Amharic language.

Church officials were given 24 hours to vacate the property last Wednesday, but they stalled until today seeking a letter of explanation. A church source said the keys were finally turned over to an official who came with five armed soldiers on his third attempt to take posession.

The present Marxist government of Ethiopia separates church and state and proclaims religious freedom as long as churches do not oppose the government.

In addition to Sweden's $20 million in annual aid, Swedish churches donate about $1 million to Mehane Yesus as part of about $4 million in overseas private aid the church receives for development projects, such as schools, clinics and road building.

Diplomatic sources said Sweden's message was carefully phrased so as not to contest Ethiopia's right to take property, but asked that the process be slowed down to allow for further consideration. The foreign minister, Col. Feleke Gedle-Giorgis, who was educated at a Lutheran mission school, said he would study the matter but there is no indication that the decision will be reversed.

Strapped for foreign currency and unhappy with the amount of Soviet aid, Mengistu made tentative approaches to Western Europe this year, although the United States, Ethiopia's key supporter during the reign of Emperor Haile Selassie, was left out of the process.

A revival of antireligious charges, which first cropped up in 1979, could derail the fledgling steps.

Warning of repercussions, another Western diplomat said, "They don't know what stupidity they've done yet, but they'll find out soon."

The incident is an example of how the government's often arbitrary actions, carried out by murky levels of the ruling military Dergue, can work at cross purposes with broader government policy.

The seizure was ordered as a group of 12 American Lutheran officials and lay persons was visiting the country to examine church aid projects. In a similar incident earlier this year an official in the northern city of Asmara ordered the seizure of the Italian consulate while delicate negotiations were under way in Addis Ababa, the capital, with Italian officials.

Property seizures have been common under the Marxist government, and it is possible that the state security official who ordered the takeover last Wednesday did not attach any great significance to the move.

Even under the emperor when the Ethiopian Orthodox Church was the state religion, antimissionary feeling was widespread in Ethiopia.

Traditionally, Protestant missions have been restricted to the south and west, areas inhabited by the Oromos, Ethiopia's largest tribe. The ruling Amharas have long suspected the Protestants of stirring up tribal feeling among the Oromos despite denials by the missionaries.

An organization known as the Oromo Liberation Front has carried out sporadic guerrilla warfare in the area in the last couple of years. The executive secretary of Mehane Yesus, Gudina Tunsa, is the brother of a front leader. The church official disappeared two years ago and according to some reports is in prison.

"Since Ethiopian Protestants are all Oromos and the government's difficulties with the Oromos are growing," one source said, "difficulties for the Protestants are also increasing."

Despite the other potential motives, however, Ethiopia has taken a number of antichurch actions recently. In western Welega region, 160 pastors and church leaders, all Ethiopians, were arrested in the last six months. Most reportedly have been released but the pastors' movements are limited, preventing them from serving several congregations as they have traditionally done.

Some churches have been closed and mass media equipment has also been seized. Movements of the 200 foreign missionaries, mostly Scandinavian, are also limited although none has been detained.

The headquarters of a small Baptist denomination with fewer than 1,000 members was also seized last week.

Some of the Dergue leaders are thought to be atheists, but antireligious sentiments are probably the result of Marxist ideology which does not allow room for any competing organization.

One Western diplomat summed up the takeover in this manner: "They found they needed premises for the anticorruption authority. They found the Mehane Yesus headquarters suitable.

"They also found it suitable to reduce the influence of the Mehane Yesus church because the government feels it is a platform for the Oromo Liberation Front. Looking for a scapegoat for their problems, they can thus blame foreigners."

Despite harassment of the church, Christian leaders say church participation has risen significantly since the revolution.