After a year of debate, the Loudoun County School Board approved a sex education course last week for ninth and 10th graders in the county's four high schools that will be a slightly modified version of a course offered to 11th and 12th graders.

Both are elective courses and require parental permission. However, in a 4-to-4 vote, the board denied a motion for an even more modified version of the course for sixth and seventh graders. Board members voting against the move said the decision was based on strong parental opposition in their districts.

Despite concern that it might be setting a precedent, the board also approved an after-school parent-child sex education course to be conducted by the Better Beginnings Coalition, an association recently formed to encourage sex education in the schools. It will teach sex education to both age groups in a six week course that will cost $25 to cover materials in the classes.

The marriage and family course already being taught in the 11th and 12th grades includes components on human reproduction and the possible effects of sexual relations such as venereal disease, pregnancy and forced marriage. Abortion, contraception and homosexuality are also discussed.

In the modified version for ninth and 10th graders, abortion, contraception and homosexuality are not part of the curriculum. The even more modified version the board denied for sixth and seventh graders included discussion of the human reproductive systems, its parts and functions, as well as"pregnancy and delivery.

In urging the board to approve this version, Leesburg representative Betty Poelhman said that human sexual reproduction is a body of scientific knowledge and belongs naturally in a science curriculum. Added Bonnie Epling of the Catoctin District, "I am more afraid of what my kids don't know than what they do know."

Jerry Pelkey, chairman of the county's advisory commission on youth, praised the board's actions. "Something was needed and this was a start," said Pelkey, whose commission was among those groups instrumental in bringing the discussion of sex education to the forefront a year ago. "The board did a fine job tonight."

The board's actions were a disappointment to members of Concerned Parents, a loosely knit group formed to oppose the expansion of sex education classes. Before the meeting the group presented a petition to the board signed by more than 700 people who said they were opposed to family life education courses at any grade level.

The Better Beginnings Coalition, made up of nearly a dozen civic and political groups in Loudoun, has applied for a $4,000 private grant to pay for films to be used in the after-school courses approved by the board. Students who apply will be urged to bring a parent of the same sex and participants will be segregated according to sex and age groups.

According to coalition chairman Mary Ellen Smith, coalition volunteers who will teach the course will also train county school teachers in the curriculum so that county schools can eventually take over the program. A pilot program taught in a local church early this year was "very successful," Smith said.