NAIROBI, KENYA, OCT. 15 -- Capt. Thomas Sankara, the ebullient, reform-minded leader of the small West African state of Burkina Faso, reportedly was overthrown today in a military coup.

An announcement on government radio said that Sankara, who himself came to power in a coup four years ago, had been overthrown and replaced by the country's No. 2 official, Capt. Blaise Compaore.

The report said Sankara was "a traitor and renegade" who had concentrated too much power in his hands and was leading Burkina Faso to economic, political and social chaos.

Burkina Faso, an arid, landlocked country with 7.9 million people, is the third poorest nation in the world, according to the World Bank. Its per capita income is estimated at $150 a year, and the country depends on more than $70 million in remittances sent home by Burkinabe workers employed in neighboring Ivory Coast.

In Paris, French diplomats told news agencies that the coup report appeared to be accurate. They said that the 37-year-old Sankara had been arrested.

Witnesses told news agencies that there was gunfire today near the presidential palace in the capital of Ouagadougou. They said military vehicles were seen advancing on the palace.

{Officials at the U.S. Embassy in Ouagadougou said gunfire erupted in the city about 4 p.m. and rang out sporadically until nightfall, United Press International reported from Abidjan, Ivory Coast. Other witnesses in the capital said an undetermined number of people apparently were killed in an attack on Sankara's residence.}

The country's land borders were closed and a curfew was imposed from 7 p.m. to 5 a.m.

The ouster of Sankara, if true, would end the rule of one of modern Africa's most unorthodox and original leaders.

Since 1974, Sankara, a tall, lean former paratrooper with the dashing good looks of a movie actor, has attracted continent-wide attention as one of a new generation of African leaders.

Along with his close friend, Flight Lt. Jerry Rawlings, the military leader of nearby Ghana, Sankara rejected personal wealth, demanded an end to factional politics and insisted on public accountability by government leaders.

Sankara, who came to prominence in the mid-1970s as the hero of a border war with Mali, composed "revolutionary music" on his guitar and performed it in the capital. He insisted that women be given legal equality with men. He ordered the government to sell off its fleet of Mercedes limousines.

In a public accounting last year of his personal wealth, he listed his most valuable possessions as two guitars, one of which had cracked in the desert heat.

In 1984, Sankara changed the name of his country from Upper Volta to Burkina Faso, which, in the language of the Mossi ethnic group, means "the land of the men of integrity."

Burkina Faso is a former French colony that became independent in 1960. Since then, power frequently has changed hands between military and civilian governments.

In the past year, Sankara's demands for economic reform, including wage reductions, have become increasingly unpopular. Relations with the country's traditionally powerful trade unions have deteriorated sharply.

Compaore, announced today as the country's new leader, was instrumental in the August 1983 coup that put Sankara in power, but there have been frequent reports that the two men do not get along. Compaore reportedly felt that Sankara was pushing painful reform too fast on the impoverished country.

Burkina Faso is in the Sahel belt and is subject to frequent drought. It suffered a severe famine in 1984, but recovered last year with good rains.

When Sankara came to power, he accused his predecessor, an Army doctor named Jean-Baptiste Ouedraogo, of "neo-colonialist leanings." The same charge was leveled against Sankara by his successors.

{Radio Ouagadougou announced Compaore had seized power "to put an end . . . to the autocratic regime of Thomas Sankara, to stop the process of neo-colonial restoration under way by this traitor of the revolution," UPI reported.}

Sankara steered his country on an iconoclastic course in foreign policy. He formed relatively close links with Libya, but at the same time vowed that he would not be a "pawn" of Moammar Gadhafi.

His relations with former colonial ruler France were brittle. When French President Francois Mitterrand visited Ouagadougou last year, Sankara scolded him about France's Africa policy.

Sankara, who is well-read and fluent in English as well as French, received extensive favorable coverage in the western press. He frequently was lauded for not using his office to become rich.