PARIS - The killing of pro-democracy demonstrators by Guinean troops in September appears to have been premeditated, then covered up in organized fashion, and was not the work of rogue soldiers, Human Rights Watch said in a report yesterday.

The killings and rapes likely amount to crimes against humanity, the watchdog group concluded after an on-the-ground investigation.

A 108-page report on the Sept. 28 massacre in a sports stadium provides a description of how it unfolded and detailed accounts of particularly gruesome forms of rape and other sexual abuse.

The report concludes that members of the elite Presidential Guard headed by Lt. Abubakar "Toumba" Diakite, top aide to the military junta's president, were responsible for the massacre, as has been widely reported. Among others considered responsible by Human Rights Watch are elite gendarmes under the command of Capt. Moussa Tiegboro Camara.

Junta chief Moussa "Dadis" Camara was rushed to Morocco for medical treatment after being shot by Toumba in a Dec. 3 dispute. The former presidential guard, in an interview from his hiding place Wednesday with Radio France Internationale, admitted to shooting the junta chief, contending that there was a "betrayal of democracy" by the president who tried to blame him for the massacre.

The nongovernmental organization said the gendarme chief also is being treated in Morocco after being wounded in a separate incident of military infighting. That could not be independently confirmed.

"The serious abuses carried out in Guinea on Sept. 28 were clearly not the actions of a group of rogue, undisciplined soldiers, as the Guinean government contends," said Human Rights Watch's emergencies director, Peter Bouckaert. "They were premeditated, and top-level leaders must at the very least have been aware of what was being planned, our investigation shows."

The rights group said it interviewed about 240 victims, witnesses, military, medical staff, diplomats, and others.

The report said that on the day of the massacre, several hundred troops from the Presidential Guard along with gendarmes on the antidrug and organized-crime squad, riot police, and dozens of militiamen in civilian dress entered the stadium. Tear gas was fired, causing panic, and security forces then stormed the stadium, firing into the crowd. The report said numerous witnesses spoke of "spraying the crowd from left to right."

"Witnesses described how the panicked demonstrators were gunned down as they attempted to scale the stadium wall; shot point blank after being caught hiding in tunnels, bathrooms, and under seats; and mowed down after being baited by soldiers offering safe passage." the report said.

The organization estimated the number of deaths at 150 to 200, compared with an official figure of 57. It said hospital and other records confirm more than 1,400 wounded. Investigators also found "strong evidence. . . that the military engaged in a systematic effort to hide the evidence of their crimes," the report said.