ARUSHA, Tanzania, Dec. 3 — In the first case of its kind since the Nuremberg trials, an international court here on Wednesday convicted three Rwandans of genocide for media reports that fostered the killing of about 800,000 Rwandans, mostly of the Tutsi minority, over several months in 1994.

A three-judge panel said the three men had used a radio station and a newspaper published twice a month to mobilize Rwanda's Hutu majority against the Tutsi, who were massacred at churches, schools, hospitals and roadblocks. The court said the newspaper "poisoned the minds" of readers against the Tutsi, while the radio station openly called for their extermination, luring victims to killing grounds and broadcasting the names of people to be singled out.

The three men convicted were Hassan Ngeze, who owned the newspaper Kangura, Ferdinand Nahimana, who controlled the popular radio station RTLM, and Jean-Bosco Barayagwiza, the station's co-founder. Each of the three were found guilty of three counts of genocide and two counts of crimes against humanity. Mr. Ngeze and Mr. Nahimana were sentenced to life in prison. Mr. Barayagwiza was sentenced to a lesser term of 27 years because, the judges said, his rights had been violated early in the case. All had been in the court's custody for years.

In 100 days in 1994, prosecutors in Arusha contend, about 7 out of 10 of Rwanda's Tutsis were wiped out with a brutal efficiency. The United Nations, which failed to intervene during the massacres, set up the international court in the relative safety of Tanzania three months after the killings ended to bring the main perpetrators to account.

Wednesday's verdicts were the first convictions of media executives for crimes of genocide since 1946, when the Nuremberg tribunal sentenced the Nazi propagandist, Julius Streicher, to hang for his campaign against the Jews.

In a 29-page summary of the Arusha judgment, which was read aloud in court, the judges pointed out that they were addressing issues that had not come before an international court for many decades. "The power of the media to create and destroy human values comes with great responsibility," the summary said. "Those who control the media are accountable for its consequences."

Elated prosecutors called the verdicts a historic victory. "This is really a groundbreaking decision," said Stephen Rapp, the lead prosecutor. "The court said there is a wide range for free expression, but when you pour gasoline on the flames, that's when you cross the line into unprotected expression."

John Floyd, Mr. Ngeze's lawyer, called the judgment a major setback for free speech and an invitation to dictators to close down any media outlet on the grounds it could provoke violence.

"This is a terrible, terrible decision, the worst decision in the history of international justice," he said. He claimed that American courts, with their great concern for free speech, would have thrown the case out.

Floyd Abrams, a legal expert on the First Amendment disagreed. He said in a telephone interview that while the United States protected free speech more fiercely than any other country, it did not shield statements intended to provoke violence and likely to do so. "We would have protected some of the materials that were before the court," he said. "But even the First Amendment would not provide a basis for acquitting these defendants."

Mr. Nahimana, who argued that his radio station was taken over by extremists during the killings, and Mr. Ngeze intend to appeal, their lawyers said. Mr. Barayagwiza refused to go to court, and his lawyer made no statement after the verdict.

Besides drawing a legal boundary between free speech and criminal incitement to mass murder, tribunal officials said the verdicts vindicated the court's slow and expensive approach to delivering justice in a region where the powerful have long enjoyed impunity.

The international court has faced intense criticism. In nine years, with a staff of 872 and an annual budget of $88 million, it has produced only 17 convictions, including Wednesday's.

The United Nations recently gave the court more judges and appointed a new lead prosecutor, Hassan Bubacar Jallow of Gambia, to replace Carla Del Ponte, who was splitting her time between the Rwanda tribunal and one set up in The Hague to investigate war crimes in the former Yugoslavia.

Tribunal officials said Wednesday's verdicts showed that the court had overcome most of its troubles. The pace of trials has clearly picked up: in the past month, two new cases have begun against eight ministers of the interim Hutu government that ruled during the massacres. One verdict was delivered earlier this week, and four more are expected soon.

But there is no decision about who will investigate charges that the Tutsi organized revenge killings of Hutus after a Tutsi-controlled government came to power in mid-1994. Rwandan officials say they want to handle it themselves. Some critics say the tribunal must investigate or lose credibility with Rwanda's Hutu.

And the location of the court, 1,200 miles from Rwanda's capital, Kigali, means that few Rwandans feel a part of the process. For a court organized to impart a sense of justice and help the Hutu and the Tutsi reconcile, that is a major impediment.

Bongani C. Majola, the deputy prosecutor here, put it this way: "Rwandans say, `Listen, we are the victims, but we know nothing about what is happening there. We don't see it on the papers, we don't hear it on TV, we don't hear people in the bars talking about it. So to us, nothing is happening.' "

What the verdicts will do, said Mr. Rapp, the lead prosecutor, is help set an international standard governing the responsibility of those who control the media for hate-spewing broadcasts and articles.

The cases turned on whether the three men were deliberately trying to create a frenzy of violence, or were simply trying to arouse the Hutu to defend themselves against armed Tutsis who were trying to overthrow the Hutu government.

The three-year trial detailed how the hugely popular RTLM station turned into a messenger of death. Copies of Mr. Ngeze's newspaper showed it relentlessly denigrated the Tutsi and suggested on its cover that the machete was the best way to deal with them.

The judges found that the station and newspaper branded all Tutsi, armed or unarmed, as the enemy. They quoted a witness who testified: "What RTLM did was to spread petrol throughout the country little by little, so that one day it would be able to set fire to the whole country."

In sentencing Mr. Nahimana, Navanethem Pillay, the presiding judge, said "Without a firearm, machete or any physical weapon, you caused the deaths of thousands of innocent civilians." To Mr. Ngeze, the newspaper owner, she said: "Instead of using the media to promote human rights, you used it to attack and destroy human rights." She called Mr. Barayagwiza, an extremist political leader, the linchpin of the three men's conspiracy to incite genocide.

The court also found that Mr. Barayagwiza distributed a truckload of weapons used by Hutus to kill Tutsis and that, in one town, Mr. Ngeze ordered Hutu militias to murder Tutsis.

As gangs took to the streets with nail-studded clubs and sharpened sticks, the radio broadcasts grew increasingly chilling, court records show. One RTLM announcer advised: "Look at a person's height and his physical appearance. Just look at his small nose and then break it."

Another broadcaster discovered hundreds of famished Tutsis hiding in the dormitory of an Islamic center in Kigali. A survivor testified that the station announced that armed Tutsi fighters were in the mosque.

By the next morning, the Hutu militia had herded the Tutsi into nearby houses and lobbed grenades inside, the witness said.

Two months later, RTLM announced on the air that incredibly, still more Tutsis had fled to the mosque, hoping for refuge.

"I went there to take a look and saw that they looked like cattle for the slaughter," the broadcaster said. "I don't know whether they have already been slaughtered today or whether they will be slaughtered tonight. I feel they are all going to perish."