SAN SALVADOR, DEC. 10 -- Gunmen killed the regional leader of the government's Human Rights Commission in combat-torn eastern El Salvador last night, the second assassination of a rights activist in the past six weeks.

No group claimed responsibility for the death of Rene Joaquin Cardenas Vargas, 33, which occurred on the eve of International Human Rights Day. Benjamin Cestoni, president of the governmental commission, said Cardenas Vargas was accosted by three men and killed by a single point-blank shot through the heart as he got out of his car in front of his house in San Miguel, 80 miles east of here.

The governmental commission is charged with documenting human rights abuses in the nation's bloody civil war. It concentrates on ensuring that prisoners are treated properly, giving human rights classes to the military and technical investigations.

Cardenas Vargas had worked with the commission for two years. A government spokesman said President Jose Napoleon Duarte was out of the capital but would issue a statement later condemning the assassination.

"The commission expresses its total repudiation of this cowardly and criminal act by unknown assailants," a commission statement said. "Now more than ever the governmental Human Rights Commission reaffirms its will to work diligently for the full respect of human rights in El Salvador."

Cardenas Vargas, the first commission member killed, is survived by his wife Cecilia and children aged 12 and 8.

"What we know so far is that he was followed from his office by a Toyota car with three men in it," Cestoni said in an interview here. "One man went to the middle of the street, one stayed in the car and one went up behind him and touched him on the shoulder. When he turned around, he was shot with a 9-millimeter pistol from less than four inches way, leaving powder burns on his shirt."

On Oct. 26, unknown gunmen, also using 9-mm pistols, killed Herbert Anaya, the president of the nongovernment Human Rights Commission, a group often at odds with the governmental group.

The killing of Anaya, which most diplomats and analysts believe was the work of the far right, sparked a week of protests and marches in the capital and increased fears of stepped-up political violence. An earlier president of that commission was killed in 1983 and a spokesman has said three other members have been killed and another three were missing and presumed dead.

Cestoni said it was too early to blame anyone for yesterday's killing. The far right has been responsible for the vast majority of the political assassinations, but the far left also has killed for political motives.

The governmental commission began operating on Jan. 3, 1983. It has been criticized for focusing on guerrilla violations and seldom denouncing military abuses, while the nongovernmental commission has been accused of ignoring rebel violations.