It has become his motor, his meaning, the grief that will not go away. Nelson T. Shields 3d knows that it may not be enough to win the battle he has chosen to fight, but still, it drives him on.

He is fighting against handguns the .32-caliber Berettas, the 38s, the .22s, the machines that were used in the killing of 10,000 Americans last years. There are, of course, other ways to respond to the murder of your son. yThis has been Shields' way for five years now.

He has personalized the issue, calculatedly injected his victim status into the debate. "It has been too rational from the anti side," he said. "The opposition is emotional about their guns. We need to get people emotional about life and death and the human reality."

The human reality is pictured on the office wall: a blown-up photograph of Nelson (Nick) Shields 4th, at 23 lying in a San Francisco street, still clad in his gym shorts and sweatshirt, the final victim in the series of Zebra killings that terrorized that city in 1974.

Nick was a skier, a lacrosse player, a photographer, halfway through his college years, a cook and a carpenter and a traveler who was visiting friends when a man walked up behind him, fires three sudden shots through his back, one that exited near his heart.

Police later found the gun, a .32-caliber Beretta, and through ballistics tests linked it to several other killings and, through a painstaking tracing effort, to the mysterious Zebra killers, the black fanatics who for 179 days in San Francisco murdered whites at random.

Shields is not morbidly obsessive. He and his wife, Jeanne, see friends from the DuPont Co. in Wilminton, where he spent 26 years as a manager. He still fishes now and then up in Maine. He continues his membership at the exclusive Vicmead Country Club in suburban Greenville, Del.

But four days a week, in the sixth-floor Washington office of Handgun Control, Inc., he is lobbing for more government regulation, lobbying the wrong issue in the wrong year. He knows that. He has his eyes open.

By all appearances, Shields should be on the other side. He is Hotchkiss, Yale, corporate, Republican. He is even a hunter: quail, geese, pheasant. He owns three rifles. On the wall of his office is a disarming watercolor, a wash by Andrew Wyeth called "The Coon Hunter." "I get hell from the NRA (National Rifle Association) for bringing up the death of my son," Shields said. "They said Kennedy doesn't do it. I say 'I don't give a damn what Kennedy does' and they don't like that. They think its about rights and individual freedoms. Well, I have a right to live in a society without fear."

At first his campaign was quixotic. He demanded a ban on handguns, he marched off angrily to the Deleware office of then-Rep. Pierre du Pont 10 days after Nick's death. Fueled, he concedes, purely by pain, he used up all his vacation time at the Zebra trial.

But in May 1975, he took leave from Du Pont Co. -- never to return -- and began working with a few kindred spirits at Handgun Control. Inc., a tinly lobby that had been started the year before by a student who had been held up in Chicago.

Shields started shuttling between Greenville, where he and his wife still live, and downtown Washington, where, in the last few years, Handgun Control has been gaining some visibility. It has some pragmatic goals: passage of the foundering Kennedy-Rodino bill that would tighten loopholes in the Gun Control Act of 1968 and a publicity campaign to raise the consciousness of the American voter.

It has caught the eye of columnists, afforded Shields an appearance on CBS' "60 Minutes," publicized the political contributions of the gun lobby, produced a slick half-hour film and put together professional press kits -- complete with a giant wall poster -- on "The American Handgun War." k

The group has hardly won the hearts and minds of Congress, but it has established itself as a presence, nipping at the heels of the NRA, employing a full-time legislative lobbyist, soliciting a paid membership of about 70,000 and collecting annual operating revenues of about $250,000.

Among the grimmer tasks it has taken on is the compilation of a monthly "Handgun Body Count -- August's dead: 724; Dead since Jan 1., 1980, 5,238." (Sample item: Brooklyn, N.Y., Tyrond Hampton, 15, playing basketball on a playground, shot in the head by members of the losing team after they stole his red sneakers.")

Compiling the list is one of the jobs of the lobby's eight full-time and two part-time staffers. "They go home with the shakes every night," Shields said.

It is hard to look at Nelson Shield's gray eyes as he talks. His passion is so unexpected. He is quiet Episcopal in repose, but then suddenly evangelical once handguns are mentioned.

His fingertips trace slow circles on the ends of the chair's armrests. Most of the victims who live to think about it, or the survivors of those who don't, would like to sweep the confrontation with handguns under the rug and get on with life.

But that confrontation is Shields' life.

He is not particularly articulate, nor is he agile in debate. His last position at Du Pont was that of marketing manager in charge of automobile consumer products -- antifreeze, brake fluid and car waxes such as Rally. It did not require a great deal of skill in public speaking.

As chairman of Handgun Control, he has taken on the lions in their own den. He has debated at the International Association of Big Game Hunters meeting in San Antonio, arguing for stricter handgun laws.

He testified in Congress. And on one memorable day last spring he found himself before an audience-participation show in Nashville peering out at 70 hostile pro-gun interrogators.

He sat at the counter of Marigolds around the corner from his suite of offices, and recalled the incident, "I told them I felt sorry for them," he said. "They didn't trust anybody. 'You don't trust your federal government,' I told them. 'You don't trust your police and you don't trust democracy.'

"'The only thing you seem to trust,' I told them, 'is yourself and that piece you're carrying.' Well, they rose up as one," Shields said, "and they sent up a shout: 'You're right,' they shouted. 'You're right.'"

Shields stood there, waited for their applause to die, and continued.

In the end, he believes, he is irrefutable.