SAN SALVADOR, OCT. 26 -- Gunmen shot and killed Herbert Anaya, the president of the private Salvadoran Human Rights Commission, today and a commission official blamed death squads linked to the government.

Tonight, Police said about 800 political prisoners took over the headquarters of the country's main prison, Mariona, five miles north of here, to protest the killing. No violence or injuries were reported, and prison authorities were making no moves to force the prisoners to return to their cells.

In the capital, a crowd of about 200 people burned two vehicles and blocked traffic.

A police sergeant said two unidentified men shot Anaya, 33, this morning "at point-blank range" after he had dropped off two of his five children at school. Anaya's wife, Mirna Perla, said she discovered her husband in the family car when she took their other children outside so he could take them to school.

Officials said Anaya's killers had shot him once in the face, twice in the body and once in the arm with 9-mm automatic pistols. No group claimed responsibility for the killing.

Reynaldo Blanco, a spokesman for the Human Rights Commission said, "The murder of Herbert Anaya is the sole responsibility of {President Jose} Napoleon Duarte and the military high command, which takes its orders directly from the U.S. Embassy." Blanco told a news conference at commission headquarters that the killing was "the work of the death squads tied to the security forces."

Anaya is the second commission president to be killed. In 1983, Marianelea Garcia Diaz was slain. Blanco said three other commission members have been killed and three others have disappeared and are presumed dead.

Government spokesman Roberto Viera said at a news conference that the government "condemned and repudiated" the killing and said it was an attempt to endanger a regional peace plan signed by five Central American presidents this summer.

The killing "was carried out at a time when we are carrying out efforts to look for political solutions through dialogue, amnesty, a cease-fire and other actions," Viera said. "This murder is a hard blow to those who believe in and look for political solutions."

He said it was the work of "extremist elements seeking to destroy the entire process we have been building." He promised a full investigation.

One West European diplomat said, "It could not have come at a worse time for everyone. Whoever did it chose the critical time. It is clearly an effort to sabotage any forward momentum.

"It could be the spark that ignites the discontent and frustration people feel with the government," another analyst said of the murder. "It could be serious trouble."

Following Anaya's slaying, leftist rebels said they were analyzing whether to continue peace talks with the government, set for Oct. 30 in Mexico City. "It makes no sense to talk with a government about democratization when the government continues its dirty war against civilians, under the reign of the death squads," a rebel statement said.

A broadcast by rebel Radio Venceremos announced in "the next hours" the leftists would begin a transportation stoppage aimed at paralyzing the nation's traffic in "repudiation of the coldblooded murder."

{The human rights organization Amnesty International called on the government for a complete investigation, saying it had sent a message to Duarte in August expressing concern over what it said were threats against Anaya by Salvadoran police agents.

{In Washington, a State Department official said, "We can categorically deny that any killing has ever been ordered by the U.S. Embassy." Another State Department official, Jim Callahan, desk officer for El Salvador, said the United States has been "very active" in helping the Salvadoran government improve human rights conditions.}

The Human Rights Commission was founded in 1978 and Anaya joined in 1980. The U.S.-backed Duarte government has accused the group of being a front for leftist guerrillas and of favoring rebels by not reporting rebel abuses.

In a newspaper advertisement June 5, the commission asked police to explain why Anaya's house was under constant watch. Anaya was arrested in May 1986 on suspicion of helping the rebels. He was one of 100 prisoners freed in February in exchange for an Air Force colonel held by the rebels.

Duarte recently proposed an amnesty that church officials and human rights groups say would make it impossible to prosecute those involved in right-wing death squad killings or other "political crimes" since the war began eight years ago.

Church officials and human rights groups say of 61,000 people killed in the war, at least 40,000 people were killed by right-wing death squads.