PHNOM PENH, Cambodia - Khmer Rouge guards killed babies by battering them against trees under an official policy to ensure that the children of the brutal Cambodian regime's victims could never take revenge for their parents' deaths, the regime's chief jailer testified yesterday.

Kaing Guek Eav, alias Duch, said he was to blame for the killing of infants as commander of the Khmer Rouge's notorious S-21 prison in Phnom Penh in the 1970s. As many as 16,000 men, women, and children are believed to have been tortured there before being sent to their deaths.

"I am criminally responsible for killing babies, young children, and teenagers," Duch, 66, told a U.N.-assisted tribunal. He never mentioned whether he personally carried out such killings. "It was done by my subordinates. I do not blame them, because this was under my responsibility."

The genocide tribunal is trying Duch for crimes against humanity, war crimes, murder, and torture. An estimated 1.7 million Cambodians died under the 1975-79 communist Khmer Rouge regime from forced labor, starvation, medical neglect, and executions.

Last year, the tribunal took Duch to S-21 - which is now a museum - and the area where prisoners were executed, and he was shown drawings of Khmer Rouge guards swinging babies by their legs and pounding their heads against tree trunks.

"The horrendous images of the babies being smashed against the trees, I didn't recognize it at first," said Duch. But he admitted that after also seeing photographic portraits of children who had been held at S-21, he recalled such things had happened.

Duch said official Khmer Rouge policy dictated that detained offspring of prisoners at S-21, also known as Tuol Sleng, must be killed to prevent retaliatory action. It is not known how many young children were killed at S-21.

Duch is the first senior Khmer Rouge figure to face trial and the only one to acknowledge responsibility for his actions.