Nancy Wells, a slender woman with a jeweled American flag pinned to her navy blue lapel, had barely sat down at a recent review session of film strips for sex education classes in Montgomery County before an offending slide was beamed against the wall.

Wells asked for light, pointed out a birth control device on a shelf in a doctor's office, and resolutely said the slide, proposed for eighth graders, had to go. Wells' complaints drew grumbles from the others sitting in the stark meeting room.

"These people think 13-year-olds are obsessed with their sexuality," said the 50-year-old Wells later of the 29-member committee that reviews all material for sex education courses. Wells has been a committee member since last year. "We are consistently seeing material that says to children 'enjoy your sexuality but remember your contraception.' Someone has got to watch them."

And watch them Wells does. Armed with notebooks and satchels of textbooks with offending passages underlined, Wells is part of a persistent cadre of classroom observers that has challenged the teaching of sex education in Montgomery County public schools. At the moment, Wells and her supporters are at the center of what has become one of the year's most acrimonious and emotionally charged discussions: Should eighth graders be given information about contraceptives?

On one level, school board members, trying to stem the intensity of the debate before a vote tonight, argue the issue is academic. High school classes already include information about contraception and the change would mean a difference between receiving the information in the eighth grade rather than the ninth. The proposed junior high course would involve, at most, two classes and a sheet and a half of definitions on different methods of birth control.

But staff members and community leaders say the issue is larger than board members want to acknowledge. It is, they say, a question of whether a relatively small, vocal group of citizens can determine what is taught in the public schools.

"There is abroad in this land a very small group, a very minuscule minority, who are trying to manipulate the system and thwart what are legitimate goals that have been agreed upon by a broad consensus," says Carl Smith, principal at Bethesda-Chevy Chase High School.

"That in a sophisticated and highly educated community like Montgomery County we should still be arguing about this issue is ludicrous."

Not so, say Wells and the two other women who have come to dominate the forces against sex education in the county, Mary Bailey Bowen and Olga Fairfax. None of them have children in county schools any longer, but they argue if they didn't stalk the libraries and school health fairs, make persistent inquiries of school staff and demand course outlines, material that undermines traditional family values would be more pervasive than what they say it already it is.

"The schools are trying to change the whole moral fabric of society," says Bowen, chairman of CURE (Citizens United for Responsible Education), a group that has a membership of about 100 but thousands of supporters, according to Bowen. Bowen, 54, has led the charge against sex education in the county since 1972 when she became involved in a suit charging the board with violating state guidelines by including erotic material in sex education courses. Last year, Bowen, a Republican, failed in a bid for the Maryland House of Delegates.

By teaching sex education, "authoritative figures are giving tacit approval to sex before marriage," Bowen says, speaking from her kitchen table and surrounded by literature she says she has gathered from various schools and Planned Parenthood centers.

The obsessive nature of the attack by Bowen and others disturbs some members of the citizens' review committee. "They're like Captain Ahab and Moby Dick with sex education being the big white whale," says Larry Levin, one such member. "They see it everywhere and are compelled to either slow it down or stop it all together."

Yet Bowen, Wells and Fairfax have had a receptive ear for most of the last four years when the school board was dominated by a conservative faction. They scored a major coup last year when the board instituted major revisions in how material for sex education is approved and put Wells and Fairfax on the citizens review committee. That same board also disapproved birth control information for eighth graders.

But a new majority took office in January, and on Monday night, those more liberal members are expected to reverse their predecessors and approve the eighth grade program.

Bowen and Wells are a formidable foe. Since May 1, almost 1,700 letters opposing the eighth grade unit--the overwhelming majority of them form letters--have poured into the board office. Only 61 supporting letters have been received. Telephones have rung continually.

Staff members, outraged by the never-ending requests for information and public flailings they have received from Wells and Bowen, frequently refuse to answer any questions that are not put in writing. "It's been nonstop guerrilla warfare on the intellectual front," says one staff director.

Ed Masood, director of the department that oversees sex education courses, agrees. "These people have been abusive," he says. "They walk in off the street and expect to be catered to. Then they use the information in ways that are totally inaccurate."

One day last week when Bowen visited Masood's department, work was interrupted for a good part of the afternoon, according to Bowen and Masood. When the material she wanted was not available, she asked that Masood and an assistant sign a statement to that effect. They refused. She then proceeded to three other offices, including the office of Superintendent Edward Andrews. Andrews slammed his door and said he would not speak to her.

Despite such vigilance--and warnings from Bowen and the others that they will step it up if the contraception unit is approved--five of seven board members who support the unit do not believe the letters represent a majority of parents.

"There does not appear to be a reciprocal organization on the part of pro-groups," says board member James Cronin. " But testimony we have received from a large number of parent and social organizations indicates there is broad support for giving eighth graders this information."

Among those groups who have shown such support are, the county's council of Parent-Teacher Associations, the council of student government leaders, the county's mental health department and the Commission on Children and Youth.

The fight over sex education in the county dates back to 1972, when Parents Who Care filed suit against the school board. The group said the board was invading the privacy of the family and violating its own guidelines by including material in sex education courses for high school students that depicted erotic sexual behavior.

In 1976, after more than four years of hearings before the state board of education, Parents Who Care won something of a victory. While the state board rejected most of the group's major claims, state officials did note that some material was in violation of state guidelines and directed the school system to review it all.

Since then, school officials say, groups spawned by Parents Who Care, including CURE, have waged a nonstop battle. The fight heated up last year when Wells and Fairfax, a former county school teacher and now a leading antiabortionist in the state, joined the 29-member Citizen Advisory Committee on Family Life and Human Development.

When they began reviewing all material used in sex education courses, havoc broke out.

What they say they found was obscene material, passed on by staff members to the committee for review, that advocated erotic and perverse sexual behavior. They went public with complaints to the board and staff. Some of the literature they were asked to review they discovered had been banned by the school system in earlier years.

Two books brought to the committee for review--Boys and Sex, and Girls and Sex--talked about methods of oral sex and ways to masturbate. The book had been banned in 1973 from school libraries.

What ensued was a nasty public battle, waged from the pulpit and the barber chair. It resulted in a total revision of policy for the committee and the support staff, a reassignment of the sex education coordinator and the eventual elimination of the eighth grade unit on contraception after it was piloted successfully, with parent support, at three junior high schools.

"Every single month we were absolutely shocked by the material that had either been passed on to us by the staff or had been approved earlier by the citizens' advisory committee," says Fairfax, who became interested in the antiabortion fight and sex education after a friend had an abortion and she, herself had a miscarriage. To make her point, Fairfax frequently carries a jar containing an aborted 12-week-old fetus with her.

After the complaints were made, some of the material was withdrawn and Lois Martin, associate superintendent of instruction, apologized for some literature that had been passed onto the committee. The staff, Martin said, was merely sending to the committee all literature they received from publishers. Martin and other staff members complained that Bowen, Wells and their followers were passing out Xeroxed literature of the material that either took sentences out of context or implied that a book already was being used.

Bowen responds that such staff reaction was just an excuse for sloppy work.

"Who likes to be reminded that they're not doing their work properly?" she asks.