NAIROBI, KENYA, SEPT. 4 -- Long-simmering resentment over state suppression of the Roman Catholic Church in the central African state of Burundi was the driving force behind the military coup that ousted the country's president, informed diplomats said today.

Col. Jean-Baptiste Bagaza, who had controlled Burundi for 11 years, was deposed yesterday while he was attending a conference in Canada. He rushed back to Africa today, but with Burundi's international airport shut down, he did not go on to Bujumbura, Burundi's capital, after landing at the Nairobi airport.

{Bagaza left Nairobi for Paris Saturday after apparently being denied entry to Kenya, Reuter reported. He spent 12 hours at the airport before boarding the same Air France plane that had brought him from Quebec, the agency said.}

Kenya traditionally has been reluctant to grant asylum to the losers in Africa's frequent coups.

Bagaza, 41, who came to power in a military coup in 1976, refused to speak to reporters here.

Diplomats here and in Washington said that a series of repressive anti-Catholic decrees ordered by Bagaza had caused anger throughout the country. Burundi, a nation the size of Maryland that won independence from Belgium in 1962, has 5 million people, 65 percent of whom are Catholic.

"It had reached the point where one more decision against the church would have sent people out in the streets," a senior European diplomat who served in Burundi for four years said in a telephone interview.

Bagaza's anticlerical policies, which have forced more than 450 foreign priests to leave the country since 1980, have become more extreme in the past 12 months.

Bagaza shut down a Catholic school program that provided primary education for 300,000 rural children. He banned rural prayer meetings. In June, he banned weekday church services.

"With the ban on church services, a lot of senior people in the government began to complain," said one diplomat. Another diplomat said that Bagaza "had become a nuisance; he was afraid of everything and everyone, particularly foreigners."

Bagaza had led a tribal minority government. Members of his tribe, the Tutsi, dominate the government and the military. The Tutsi, however, are outnumbered 6 to 1 by members of the majority tribe, the Hutu. Animosity between the two tribes is heightened by a legacy of tribal genocide. In 1972, Tutsis massacred about 100,000 Hutus.

Bagaza is known to view the Catholic Church as a vehicle for Hutu revolution. Most Hutu are Catholic.

During the bloodless coup, Radio Burundi said that the government was being taken over by a "military committee for national redemption led by Maj. Pierre Buyoya."

Buyoya, 38, is from the same Tutsi clan as Bagaza. Diplomats said the new government probably would maintain Tutsi dominance.

Buyoya, who was trained at the Royal Military Academy in Brussels, was chief of operations and training in Burundi's Defense Ministry, which receives funds from the U.S. government. Diplomats said he has frequently been a guest at U.S. Embassy cocktail parties.

Buyoya had been suspected of plotting coups in 1984 and 1986, a State Department official in Washington said.

Radio Burundi made only one new announcement today. It said: "Peace prevails in Burundi. All Burundi citizens are therefore requested to carry on their duties. The military committee for national redemption is working tirelessly to set up new institutions. All patriots should support the Burundi armed forces."

Reports reaching Washington from Bujumbura confirmed that the capital remained peaceful today.

"It didn't really look like a coup," one State Department official said. "There was no fighting or problems. It seems to have been an in-house coup."

Another indication that the coup was a rather clubby affair among Tutsis was the absence of any denunciation of the ousted president on Radio Burundi.