Sirens wail through Nan Rodney's Springfield neighborhood once a month, a doomsday dress rehearsal that frightens her two children so much that the 44-year-old housewife has turned her kitchen into the headquarters of the Northern Virginia Nuclear Freeze campaign.

A 69-year-old carpet salesman named Sam Schmerler, head of the Baltimore chapter of SANE (the National Committee for a Sane Nuclear Policy), carries on a cause he first embraced in 1958 when he worked to keep atomic fallout out of mother's milk.

And in the student lounge at the Georgetown University law school, over the din of pinball machines and soap opera theme music, John Oller, a 25-year-old student, recalls his moment of illumination at a Veterans Day teach-in on nuclear war. "It dawned on me how serious this issue is," he said quietly. "Nuclear war is something no one is going to survive. We're pouring all this money into the military and we're all going to die."

In the Washington area, and across the country, a movement is being born. A new generation unfamiliar with the struggles of the past has joined activists of another era to protest the threat of nuclear weapons.

In recent months the Reagan administration's discussions of nuclear strategy and its emphasis on building up American defenses have made the specter of nuclear annihilation nearly palpable to many people for the first time since the easing of Cold War tensions in the late 1960s. The concern was so widespread that the president sought to allay it week before last in a highly publicized speech.

According to a recent poll, seven of 10 Americans fear that nuclear war could erupt between the superpowers and that fear has invigorated such arms control groups as SANE, whose membership has nearly tripled in two years. And SANE is not alone.

The nationwide Nuclear Freeze campaign, which began in March at Georgetown University and since has established petition drives in 20 states, attracts nearly 100 people to monthly educational meetings in Northern Virginia. About 200 people a week are joining Physicians for Social Responsiblity, a national educational group that addresses the medical effects of nuclear war. And, in April, a week-long nationwide teach-in on aspects of nuclear war is planned by a nonpartisan group called Ground Zero.

"The movement owes its momentum to Reagan," says John Marks of the Union of Concerned Scientists. "What binds these people together is the notion that the world is getting closer to nuclear war. People don't feel safer with more missiles. What's going on between Russia and the U.S. is equivalent to two kids standing up to their knees in a room full of gasoline. One has five matches. The other has 10. The one with 10 says, 'I feel more secure because I have more matches.' "

Events in the United States cannot yet compare to events in Europe where, echoing ban-the-bomb protests of 20 years ago, hundreds of thousands of demonstrators have spilled into streets and squares to protest the deployment of nuclear weapons. But the new concern showing around the country, especially in Washington, harkens back to the activist fervor, if not style or scope, of demonstrations during the Vietnam era.

And just as in the Vietnam era, the ideological spectrum stretches from Marxist-oriented thinkers who want unilateral disarmament to accompany a radical restructuring of the economy to people alarmed by the general level of tension in the world. Many activists are going out of their way to keep the campaign focused exclusively on the nuclear issue. Many speak of the need for a strong defense, mindful of the mandate handed Reagan and proponents of a bolstered military in the 1980 elections.

The burgeoning movement draws heavily from the ranks of disempowered liberal Democrats, but organizers stress that "partisan politics stops at the edge of the mushroom cloud," and point to examples of doctors, businessmen and clergy at the forefront of the crusade.

The campaign in Washington is a blend of such national organizations as the Coalition for a New Foreign and Military Policy and such local groups as the Washington Peace Center. There are an estimated 40 groups working in disarmament and antinuclear issue, with many more signing their names to the effort.

They employ slide shows, teach-ins, phone-a-thons, mail campaigns, petition drives, peace marathons and walks, lots of "dialoguing with the grass roots," and that venerable standby of activists, the folk song. A few weeks ago strains of "We got to tell old Al Haig, make a change, make a change" filled the sanctuary of the Presbyterian church on New York Avenue -- a center for Vietnam War protests -- as members of a disarmament conference sang protest songs before a march to the White House.

"What we're seeing is a movement more deeply rooted than in the '60s," said Dana Powell, of the ecumenical Christian community called Sojourners. "The church is in the leadership. Church leaders are willing to stick their necks out and say, 'The arms buildup goes against our faith and our gospel.' "

Along with four other church groups, Sojourners drafted a pact, the New Abolitionists Covenant, which calls on Christians to say "no" to nuclear war as they once did to slavery. Since August 225,000 copies have been distributed.

The paths are many that lead to participation in the disarmament and antinuclear work. Environmentalists otherwise fighting nuclear power plants have joined over the issue of weapons waste which accounts for 95 percent of nuclear waste. Women's groups chanting "Take the toys away from the boys" see in the campaign the principle of the women's movement that puts mediation ahead of combat. The cause gets help from people who have opposed the draft and people who connect the losing battle to preserve social programs to the great sums spent to build up the military.

For Nan Rodney the questions of nuclear disarmament boiled down to personal considerations: her two children, 5-year-old Jonathan and 3-year-old Daniel.

"The first thing I think about when the civil defense siren goes off is my children," says Rodney, who as coordinator for the Nuclear Freeze campaign in Northern Virginia writes letters to newspapers, attends Freeze meetings once a week, and helps circulate petitions that call for a bilateral halt to the testing, production and deployment of nuclear weapons, as well as to the missiles and aircraft that deliver them. "I've never done anything like this before, and now it's pretty much a full-time job."

While Rodney organizes, 64-year-old Josephine Williams contributes to the struggle for disarmament by baby-sitting Daniel and Jonathan. "I have arthritis and my night vision's bad, so I can't even drive people to meetings," Williams said. "I wanted to do something, so I volunteered to baby-sit while Nan was out."

Even Jonathan has done his part in the crusade, expressing his considered views in a July 24 letter to Ronald Reagan. "If there was a bomb dropped on the earth, millions of people could be killed," he wrote in large shaky print. "I'm afraid if a hundred bombs were dropped on the earth, the earth might get destroyed."

In the past month Freeze campaigns have collected 1,000 signatures in Prince George's County and 5,000 in Montgomery, mostly at card tables set up in shopping malls. (In vintage Montgomery fashion, the organizers are mulling legal action against shopping mall managers who have have denied them access.)

"I think we're seeing the beginning of a mass movement," said Chad Johnson, 56, a retired foreign service officer. "It's the overriding issue of our time. Political affiliation hasn't been a question that seems very relevant."

But people in the movement are hunting for ways both to broaden its base and keep the issues from getting tangled up in partisan politics. Earl Molander, whose brother Roger, a former National Security Council aide, founded Ground Zero, says their organization is committed to getting the issues discussed, not pushing a point of view.

"If people think we should build more nuclear bombs they should be able to speak their minds without having someone throw blood on them," Molander said.

The tactics being charted by students at Georgetown University law school bear little relation to the helter-skelter street demonstrations of earlier student campaigns. The law students at Georgetown generally are a cynical and fairly conservative group whose conversations are sprinkled with such words as "substantive" and whose concerns revolve around grades and jobs and getting ahead. But 600 of them packed the moot courtroom for a two-hour program on nuclear war issues, one of 150 campus convocations around the nation sponsored by the Union of Concerned Scientists, on Veterans Day.

A group continues to meet under the auspices of the school's Environmental Law Forum, and has planned a letter-writing campaign, and brainstorming sessions devoted to coordinating campuses across the country, and making disarmament the issue of the 1982 elections.

Leslie Mandel, 24, a law student, is one of the student organizers. She spent a month planning the teach-in, taking time from courses and her work as a part-time law clerk, to press the cause. She can remember a time as a little girl swinging on a swing set and singing "America" when she was filled with unalloyed feeling for her country. Her father stopped her, and explained about the war in Vietnam. But there is a dire difference between ending a war and preventing a war. "This issue," she said, "can't be tangible until it's too late."