In Loudoun County, "sex education" in public schools consists of little more than a clinical chapter on human reproduction in high school biology, a warning about venereal disease given during gym class, and--for seniors only--a course on family and marriage offered by the home economics department.

The Citizens Committee on Teenage Pregnancy would like to change all that.

The group, which says that 200 Loudoun teen-age girls get pregnant every year, is circulating a petition asking the School Board to start a comprehensive, state-approved program on life, family and sexuality in the public schools. The group wants it to include a discussion of contraceptives, abortion and masturbation.

Not surprisingly, the eight-member board has sidestepped the issue in the past because of its controversial nature.

"We are hesitant to get into a debate on sex education in the schools because of what happened in Fairfax County," said School Board Chairman William J. Maykrantz. "We thought it was best to make our approach to sex education low-key. But if enough of the public wants it taught in the public schools, then of course we will consider doing so."

What happened in Fairfax County was a two-year emotional debate on the moral issues of teaching sex education in public schools. The result was a specially designed course that includes a discussion of morals, but few people seem to be happy with the end product.

Aside from Fauquier County, Loudoun is the only jurisdiction in Northern Virginia that does not include some sort of comprehensive sex education program in its school curriculum. Alexandria recently started an optional sex education program for ninth graders, who next year will be required to take the course. Arlington has sex education courses in the middle and senior high schools, and Prince William County includes sex education in a required physical education and health course. Falls Church also has a sex education program that is generally well regarded by area educators.

"If we're going to get into that same debate, we're going to do it slow and easy," said Maykrantz. "We will hear from everyone before we make our decision."

Maykrantz concedes that teen-agers do not learn enough about sexuality in Loudoun public schools. "Virtually every student gets through the reproduction part of biology, but I don't think they apply what they've learned there to dating," he said.

But he also says some parents and officials have told him in the past that sex education belongs at home. There has been no public opposition to the petition to date, however.

Janet Perry, founder of the Citizens Committee on Teenage Pregnancy, disagrees. "Kids tell us their parents are uncomfortable discussing sex with them," said Perry. "The state sex education curriculum we advocate deals with the whole spectrum of life, from birth to death. But around grade eight, it gives students the straight information about sex they need to make rational decisions."

Perry said hundreds of county residents have signed the petition, which she hopes to present to the School Board next month. The committee also is sponsoring informational workshops in which an official from the state education department explains the sex education curriculum and answers questions.

Three School Board members attended one such workshop last week. Afterward they were noncommittal, but they did encourage the committee to get signatures from all of the county's 31 school districts.

Some teen-agers in the county who cannot talk to their parents about sex and learn little about it in the public schools find alternative sources of information, mainly in local church youth programs. Several churches have created sex education seminars, such as that offered by the Christ the Redeemer Roman Catholic Church in Sterling Park.

There, youth minister Mary Ann Kerins holds a series of seminars dealing with reproduction, teen-age sexual pressures and morality. But Kerins said she too would like to see some form of sex education taught in the public school system.

"There is certainly a need for these young people to get some good, solid information," she said. "I would like to see the schools teach reproduction and the psychology of teen-age sex and let us deal with discussions of moral values."