BUJUMBURA, Burundi (AP) _ The Tutsi-led military has staged an apparent coup against the Hutu president of Burundi, who took refuge today at the U.S. ambassador's residence.

President Sylvestre Ntibantunganya fled to the ambassador's residence after a Tutsi-dominated political party rejected him as head of state and Tutsi paratroopers arrived at main government buildings in the capital.

``The president feared for his life and his own security forces were not responding to his requests,'' said Mames Bansubibko, a close adviser to the president. ``He is staying with the U.S. ambassador to make sure he is not going to be killed.''

In Washington, an administration official said the military was attempting to depose Ntibantunganya and he was expected to flee to Tanzania.

``The United States will not, under any circumstances, tolerate a government installed by force or intimidation in Burundi,'' U.S. State Department spokesman Nicholas Burns said.

Lt. Col. Nicodemus Nduhirubusa, adviser to the Tutsi prime minister and a military leader, denied Washington's claim. ``I can't see any sign of a coup,'' he said.

The capital streets were calm today, just as they were in 1993, when the first democratically elected Hutu president was assassinated.

Bansubibko said the president was not resigning. But diplomats, speaking on condition of anonymity, said it was unlikely Ntibantunganya would remain in power.

Ntibantunganya met with U.S. Ambassador Morris Hughes to determine his next move.

``The most important thing right now is to make sure that the population in Burundi will not start killing each other,'' Bansubibko said.

More than 150,000 Burundians have been killed in a civil war that has ripped the tiny African nation apart for the past three years. Hutus make up 85 percent of the population of 6 million and Tutsis make up 14 percent.

Ntibantunganya, 40, was pelted with stones and cow dung Tuesday as he arrived for a funeral for 340 Tutsis, mostly women and children, massacred Saturday by Hutu rebels in Bugendena, in central Burundi.

Late Tuesday, the usually tight security around the capital was heightened. Tutsi paratroopers were stationed at the government-run radio and TV stations, and outside government buildings.

Earlier today, the junior partner in the coalition government rejected both Ntibantunganya and the 1994 agreement setting up the current government, a weak coalition of the two ethnic groups.

``The presidency of Sylvestre Ntibantunganya is a total failure. Instead of being the president of the country, he is the head of the Hutu ethnic group,'' Charles Mukasi, the president of the Tutsi-dominated UPRONA party, said at a news conference in Bujumbura.

``He is guilty of high treason and must be toppled.''

Mukasi, also a Hutu, said the party's decision to renounce the 1994 pact technically dissolves the government.

``We are speaking to others to build a new government and elect a new president,'' Mukasi said. ``The process will start today in order to bring peace and security to Burundi so that violence can end.''

The pact followed the October 1993 assassination of Burundi's Hutu president, Melchoir Ndadaye, which threatened to plunge the tiny nation into chaos. Widespread violence followed, and thousands of people, mainly Tutsis, were killed by Hutus.

Still, the convention kept a government in place.

Ntibantunganya has been president since April 12, 1994, six days after President Cyprien Ntaryamira died in a mysterious plane crash with the Rwandan president. He knows the horrors of ethnic hatred _ his wife was killed in 1993 by rebel troops who had come to arrest him.

UPRONA's rejection of Ntibantunganya as president today was the third time the party has tried to change the September 1994 agreement that it and 11 other parties approved.

Previously, UPRONA succeeded in removing the Hutu speaker of the National Assembly _ who would have been in line for the presidency _ and in obtaining the resignation of the Tutsi prime minister, who ignored their directives.

Leonce Sinzikayo, speaker of the national assembly and a leader of the Hutu-led FRODEBU party, did not condemn UPRONA's decision today, but he urged all parties to participate in negotiations to prevent a military takeover.

Both the Tutsi-dominated army and Tutsi political parties have condemned a call by Ntibantunganya and Tutsi Prime Minister Antoine Nduwayo for foreign military help to restore security.

Many Tutsis say the plan is a plot by the president to destroy the Burundi military and expose Tutsis to a genocide similar to that which erupted in Rwanda two years ago, leaving half a million people dead.

Clashes involving the Tutsi-dominated army and Hutu rebels have intensified this year, and human rights observers say both sides routinely kill civilians.