She is not a show-stealer by either ambition or temperament. But the other morning, Randall Forsberg, the director of the Institute for Defense and Disarmament Studies in Brookline, Mass., and a woman who is one of the founders of the National Nuclear Weapons Freeze Campaign, couldn't help it.

With Sens. Edward Kennedy (D-Mass.), Mark Hatfield (R-Ore.), several representatives, a Methodist bishop, two college presidents, Averell Harriman, Paul Warnke and others sharing the stage and microphone at American University to support a bilateral nuclear weapons freeze, it was Forsberg who commanded attention.

She had the numbers, not merely the oratory. She told of the 159 out of 180 town meetings in Vermont in which citizens voted this month for the freeze. In March 1981, with the juices of Yankee outrage just beginning to flow, the number was only 14. Freeze resolutions have passed overwhelmingly in the legislatures of Connecticut, Oregon and Massachusetts, as well as the Houses in Wisconsin, New York and Kansas. Organizers in four other states--California, Michigan, Delaware and New Jersey--have begun statewide initiatives for referenda. Two-thirds of all congressional districts and 43 states have freeze activities.

With unprecedented speed, these numbers from all parts of the country have been matched by corresponding numbers in Congress. Seventeen senators and 115 House members announced last week their endorsement of the nuclear weapons freeze. If "power to the people" marked the populism of the 1960s, power from the people may be the strength of the 1980s.

For the first time, Congress feels safe in aligning itself with the public's fear and anger that the weapons frenzy has gone too far. The citizens in the meeting halls from Vermont to Oregon are not the radical left who rally behind Daniel Berrigan, nor are they about to follow Archbishop Hunthausen of Seattle, the brave tax resister.

They aren't much more than straight-arrow folk listening to freeze leaders who say that with the United States and the Soviet Union having 50,000 nuclear weapons but only 800 large cities and towns in each nation as possible targets, the zones of madness have long since been entered by U.S.-Soviet leaders.

After the American University assembly, I met with Randall Forsberg. She is 38, in command of her facts on disarmament and free of ideological bents. With her institute internationally respected for its honest analysis of the benefits and risks of arms reduction, she is anything but a peace hobbyist or another protester on a fun-time lark.

Speaking of the SALT II treaty breakdown, she said, "There is a lack of communication between Washington and the country. The people out in the country think that when you negotiate, you are negotiating about stopping and getting rid of weapons. The people in Washington know perfectly well that the negotiations are about managing an ongoing arms race and no one is thinking about stopping. And so people use the same words and mean very different things by them."

With the semantic problem now cleared--stop means stop, not stop but--it is impressive that this citizen movement needed less than two years to move from the fringes into mainstream national politics.

"We never canvassed the House or the Senate," Forsberg says. "We've had no mailings. The history of the last 10 years demonstrated that those direct lobbying efforts were fruitless if you didn't have a movement . . . at home. There was no point in going around to congressional offices . They would either say yes and do nothing, or say that's absurd, how can you expect us to stop the arms race during the Reagan administration? So all the freeze organizing has been done out in the country."

On the same morning that much of Congress was embracing Forsberg's plan, Alexander Haig did his best to ensure the continued growth of the freeze. He denounced it as "bad defense and security policy" and "bad arms-control policy." Haig's overkill is in keeping with the administration's call for a still larger overkill nuclear arsenal.

The freeze is new, but the sentiment isn't. Mark Hatfield, as sophisticated as anyone in Congress about disarmament, has been recalling Dwight Eisenhower's prediction on leaving office: "One of these days the people would make the governments of the world stand aside to let them have peace."