A 43-year-old Silver Spring man was found guilty yesterday of enticing two girls, aged 11 and 13, to commit sexual acts with him in exchange for cocaine and marijuana.

Paul C. Black was convicted by a Montgomery County Circuit Court jury of two counts of second-degree sex offense, one count of third-degree sex offense, two counts of possession of cocaine and one count each of possession of marijuana and distribution of cocaine. The jury deliberated for less than two hours before returning a verdict.

Judge Jerry H. Hyatt revoked Black's $10,000 bail and ordered him held without bond in the county jail until his Jan. 4 sentencing. All of his convictions could result in a sentence of more than 80 years, but prosecutors said it was likely that some of the sentences would be merged.

The two girls involved in the sexual abuse gave conflicting testimony during the four-day trial.

The younger girl testified Black had offered the girls crack cocaine while they were visiting in the basement of Black's home Oct. 9, 1989, with another man. The girl, now 12, said Black told them, "You don't get this stuff for free."

The girl, then a sixth-grader, said Black then asked both girls to perform sexual acts with him. The girl said she and her friend were in Black's house on Flower Avenue for about two hours.

But the 13-year-old girl denied in testimony that she had committed sexual acts with Black. The older girl also said Black and the girls only smoked marijuana.

Defense attorney Maureen Essex, citing the girls' inconsistent statements, attacked the victims' veracity. Essex said the sexual encounter was a "composite of stories told by the girls to authorities."

Prosecutor Frank Molony, calling the allegations "horrible and disgusting," said police were able to substantiate key parts of the younger girl's statements during a December drug raid at Black's house. Police seized cocaine and other drug paraphernalia during the raid, according to testimony.

Yesterday, an investigator for the county's Public Defender's Office testified the older girl told her in an interview that she had performed sexual acts with the defendant.

The mother of the 11-year-old girl reported the incident to authorities. The two girls, both of whom lived in Prince George's County, were being cared for by a boyfriend of the older girl's mother, police said.

Hyatt threw out two counts of contributing to the delinquency of a minor, citing insufficient evidence.