WASHINGTON — Christian comedian Keith Deltano did a lot of things at Loudoun County High School Thursday to encourage teenagers to stay away from sex. He sang bad hip-hop, told stories about oozing diapers, read from a government report on how condoms can fail, and waved a cinder block over one unfortunate male student's genital zone.

But he never once talked about Jesus. Although he often delivers one-liners tailored to his faith, Deltano gave a routine expunged of religion to more than 1,000 students at the public high school in Leesburg, Va.

Some civil-liberties advocates, skeptical of such shows, said school officials must enforce a line that is tested by religious performers who are invited into public schools to entertain and educate, but not preach.

"Having so-called secular performances or speeches in public schools by Christian evangelists" is a growing trend, said Barry Lynn, executive director of Americans United for Separation of Church and State. "Schools need to be extremely careful when they tread into these waters."

In recent years, evangelist bodybuilders and extreme athletes have toured schools nationwide with anti-drug and anti-suicide messages. The brother of a devout Christian victim of the 1999 Columbine school shootings has toured some Loudoun schools bringing with him a powerful anti-bullying presentation called "Rachel's Challenge."

Many parents, administrators and teachers see such assemblies as an effective way to convey hard-to-teach life lessons. But occasionally there have been controversies.

Last year, twin comedians Rick and Mick Vigneulle gave an anti-drug motivational assembly at several high schools in Charles County, Md., that prompted some criticism. The American Civil Liberties Union objected to fliers the duo circulated that advertised a free, off-campus pizza party during which they delivered a Christian message.

When it heard about Deltano's event, the ACLU sent a letter to Loudoun County High principal Bill Oblas. The group sought assurances that the comedian would not promote the local Christian pregnancy center that hired him or plug his religious books and videos. It also sought a prohibition on invitations to off-campus religious activities.

Oblas said he and Deltano had already established clear parameters. The principal had previewed the performance and determined that the message was "identical" to the system's sex-education curriculum, which emphasizes abstinence. He also sent notes to parents and gave students the option of not attending.

"I understand the division of church and state. To me, it's very clear," Deltano said afterward. The former middle school teacher has been speaking about abstinence for more than 10 years and said he has toured 46 states.

His Web site has two distinct portals, one for school shows and another for faith-based shows. The site also refers browsers to the text of a federal law that spells out rules for programs that receive federal funding for abstinence education.

Stephen Budiansky, father of an 11th-grader at Loudon County High, alerted the ACLU to the event. He said he was alarmed that the school system would invite a sex-ed presentation from someone who was not a healthcare professional and who has what Budiansky called "a clear religious agenda."

"There is a curriculum ... that goes through peer review and gets scrutiny from scientific experts," Budiansky said. "Teachers are very well trained to deal with questions that arise in class and to give accurate, scientifically valid information."

Students gave Deltano mixed reviews. Many cheered and laughed at his jokes; some blushed. Afterward, sophomore Megan Patlen, 15, said that she loved it.

"Abstinence is definitely the way to go," she said, describing herself as Christian.

Junior Ghislaine LeFranc, 16, said she didn't like how abstinence was "pressed" on her in her sex-education lessons and in the assembly.

"Although it's not about Christianity, there is an underlying conservative belief," she said, which she said she does not agree with.

Oblas said he thought that the students learned something. The presentation added to the school's curriculum by reaching students in different ways, he said.

They respond to his jokes, "his high energy and his loudness," Oblas said.