A 40-year-old Frederick County man pleaded guilty yesterday to sexually abusing three of his young daughters' friends during sleepovers at his home and to videotaping one of the assaults.

Hector Cobos of New Market may have drugged the girls -- ages 8, 9 and 11 -- by placing sedatives in their chocolate milk, Deputy State's Attorney Charlie Smith said yesterday, though Cobos was not charged with drugging the girls.

Cobos -- who practiced obstetrics in his native Guatemala but became an auto mechanic after immigrating to the United States -- was returned to jail yesterday in lieu of $300,000 bond. He is to be sentenced March 19 and faces up to 40 years in prison.

He pleaded guilty to one count of second-degree sex offense, two counts of third-degree sex offense and one count of producing or possessing child pornography. In exchange for Cobos's guilty plea, prosecutors dropped other sexual-assault charges. "The bottom line is we're not sure exactly how many girls this happened to," Smith said.

Cobos's attorney, Timothy T. Conlon, said Cobos is "highly remorseful" and is receiving psychiatric treatment.

"He's pleading guilty, and he in fact feels guilty," Conlon said. "He's taking responsibility for his actions."

Police arrested Cobos in February after the parents of a victim said their daughter had accused Cobos of abusing her during a sleepover, Smith said.

Two of the girls awoke while Cobos was abusing them, Smith said, but another remained unconscious throughout. The girls who woke up during the abuse told Cobos's two daughters about the assault shortly afterward but did not report it to their parents until about a year later, Smith said.

Cobos initially denied the charges and agreed to take a polygraph test, which he failed, Smith said. While talking with police after the polygraph, Cobos implicated himself and said he had made a videotape but had destroyed it, Smith said.

Police obtained a warrant to search Cobos's home and his workplace, an Amoco service station on Wisconsin Avenue in Bethesda, Smith said. In a locker at the service station, police found a videocassette depicting sex acts with the 11-year-old girl -- whom Cobos had not previously admitted assaulting. Cobos's wife and two daughters, now 7 and 9, have moved out of Maryland, Conlon said.

Cobos moved to the United States from Guatemala about five years ago, Conlon said. He could not find work as a doctor and was an auto mechanic when he was arrested last year, Smith said. His wife ran a day-care center in the couple's home.