NAIROBI, Kenya -- The ringleader of the 1994 Rwanda genocide was sentenced yesterday to life in prison for his role in the early days of an ethnic slaughter that eventually killed an estimated 800,000 people.

Theoneste Bagosora, 67, was the highest-ranking military officer convicted at the U.N. International Criminal Tribunal for Rwanda. The former colonel's prosecution was viewed as a significant step in efforts to punish war crimes.

"This victory sends a message to people like the warlords in Darfur or those committing horrendous rapes and killing in Congo," said Barbara Mulvaney, a Southern California attorney who served as chief prosecutor. "Every time one of these guys goes down, the message is: Sooner or later, you are going to be held accountable."

Judges found that Mr. Bagosora, as cabinet director of the Defense Ministry, was culpable in the deaths of former Rwandan Prime Minister Agathe Uwilingiyimana, four opposition leaders and 10 Belgian peacekeepers. He was also convicted of overseeing four days of deadly rampages around the country.

But judges rejected allegations that Mr. Bagosora and others plotted as early as 1990 to prepare for the genocide.

Tribunal officials had charged Mr. Bagosora with "conspiracy to commit genocide," hoping that a conviction on that charge would refute those who still deny that genocide occurred and claim that the violence was a spontaneous eruption of ethnic hostility.

The judges affirmed that genocide took place, but ruled that evidence was insufficient to prove that Mr. Bagosora and others conspired to commit the mass killings.

The 100-day massacre began in April 1994 and pitted Hutu extremists against Tutsi and Hutu moderates. Incited by hate messages on radio and armed by government officials, ordinary Rwandans -- including teachers, doctors and priests -- carried out much of the killing with machetes.

Yesterday's verdict brought a much-needed victory to the U.N.-sponsored tribunal, which has come under fire for spending too much time and money in prosecuting crimes that occurred 14 years ago.

By convicting the man whom many viewed as the mastermind, the tribunal has accomplished one of its chief mandates, legal experts said.

"They've done a pretty decent job of bringing to justice the people behind the genocide," said Sara Darehshori, attorney at Human Rights Watch who served as a tribunal prosecutor in 1995-97.

The court also served as a model for the development of an international justice system, including the International Criminal Court. "Just a few years ago, these kinds of crimes were swept under the rug," she said. "But in a short time, that's changed, and that is in large part due to this tribunal."

In Rwanda, where ethnic tension between Hutus and Tutsis is still raw, the verdict was received coolly.

When the sentence was announced during a meeting in the capital, lawmakers remained silent. At times, the government has clashed with the tribunal over who should try suspects.

But some genocide survivors expressed satisfaction. "This justice is going to help the victims of the genocide recover their dignity," said Didacienne Mukahabeshimana, a Rwandan human-rights activist who is half-Hutu and half-Tutsi.

Under the rules of the tribunal, a death sentence was not an option.