Harry Zain scurries through the halls of the Capitol, clutching his shopping bag crammed with papers.

Age: 27. Occupation: private citizen.

His hair is black and cropped short, his skin the color of Styrofoam. Hazel eyes, circled by dark shadows and Mr. Peepers' glasses, dart back and forth. He wears a white shirt, polyester tie, bright blue socks and cuffed pants that stop several inches above his cordovan shoes.

Harry Zain, lobbyist for lost causes, has an obsession: to persuade the legislators to lower the marrying age for women from 16 to 12 so he can wed his grade-school girlfriend.

"All men are attracted to girls of 12 and younger," Zain says, sipping a Coke at a Capitol Hill luncheonette. "A young girl is just in her flower, and nothing else in the world can make a man out of a boy. But a maturing woman makes a boy out of a man. There cannot be both women and men in the same country. Either there are women and boys, or there are men and girls. We are a nation of women and boys."

He is agitated. It hasn't come out right.

"Flower attracts maturity, and maturity attracts flower," he says softly. "A girl of 12 is the most beautiful of all. If they were allowed to wed, they would be happier. It would make them feel more beautiful than they are now."

He has nature behind him, he says. And reason. And history. "Jesus said in the Bible that girls should marry at 12," he says. He cites Snow White and Sleeping Beauty, saying the lesson of those fairy tales is clear: girls who don't marry at 12 will die.

Above all, Harry Zain says he wants to marry a girl he met four years ago in his hometown of Charleston, W.Va. He will stay in Washington until he gets his bill passed.

Harry's in love.

"I met her when she was 9 and I was 23," he says. "I saw her standing on the sidewalk across the street. She was the most beautiful girl I had ever seen."

Zain says he tried to court the under-age object of his desire, but was rebuffed by her parents who "didn't understand."

"I tried to visit her. They wouldn't let me. They didn't understand that I was willing to wait until she was past her flower, until she was 12. It upsets me that they didn't understand," he says, sadly. "Young girls have faith. By keeping them from marrying until a later age, they lose that."

Does she love Harry?

"She likes me," he says, blushing. He leans closer. There is faint odor, a musty modeling clay smell to his clothes.

"I last saw her eight months ago," he says with a nervous smile. "Her parents wouldn't let me see her."

He asked her to marry him. Her parents objected. He wrote her letters. They went unanswered.

Harry Zain took his case to the state judges. He buttonholed politicians, newspaper columnists and state legislators, one of whom agreed to sponsor his child-bride bill. It failed in committee by only one vote.

He ran for state senator and lost, beating out "No Choice" by four votes. He ran for Congress and also lost. Newspapers said he should add a Y to his last name.

In 1978, spurned in love and law, Harry Zain took his cause to the nation's capital. There, he added a few amendments: women should have no money, and Milton's birthday should be declared a national holiday. Stalking the Senators

The Capitol police have a name for people like Harry Zain: harmless, crackpots.

They wander down the hallways, stopping at every office, handing out leaflets and literature, asking to see the senator or congressman about a Very Important Matter. They are placated by tolerant aides who have learned to be polite but firm.

Harry Zain is different in one respect. At night, he goes to the congressmens' homes.

"Why shouldn't I," he says defensively. "I have a right to. They go to each other's homes when they want a bill passed. I don't consider myself a pest. After all, that's what they're here for. The senators are my servants."

He says he's visited 60 senators at home, including Sen. Paul Sarbanes (D-Md.) who was out, Sen. Barry Goldwater (D-Ariz.) who told him to come to the office and Sen. William Proxmire (D-Wis.) who was, Zain says, very nice to him. He also showed up one night at the McLean home of Sen. Strom Thurmond (R-S.C.) who told the lobbyist never to bother him at home.

After Zain startled several legislator's wives with his late-night visits, he was investigated by the FBI. And the Secret Service.

"They know I'm not going to harm anybody," he says defensively. "Why aren't they worried about one of the senators harming me?"

The FBI suggested he no longer make the visits. Harry Zain said he wasn't breaking any law. "I told him I'd try to be as discreet as I can," he says.

Some say Harry Zain is a walking timebomb, Danger UXB, a man whose psyche is wound tighter than a Jack-in-the-Box, ready to pop. It doesn't bother him, he says, if people think he's a nut.

"Because I know it isn't so," he says. "I'm a public citizen, which is the highest occupation in the country, higher than the president. I pay these people's salaries. They should not have kept me waiting three years. I'm a citizen who left his home to come to Washington for something he believes in."

Zain lives alone in a northwest Washington efficiency. "Across the street from Senator Goldwater," he points out. "One block from Senator Hollings, two blocks from Senator Harry Byrd, three blocks from. . . ."

He has a bed, a table to write on and a small refrigerator. He works at night as a typist for a Farragut Square word processing company, drinks chocolate malts at hotel coffee shops and rides the bus to Capitol Hill every afternoon where his face has become as familiar as Tip O'Neill's.

Harry Zain doesn't have any friends. He says he doesn't need any.

"The only friends I want," he says quietly, "are the senators themselves." The Burning Flame

Born in Charleston, W.Va., the oldest of three children, Harry Zain went to Catholic schools, where he earned mediocre grades and a reputation for being religious, if slightly eccentric. He liked to read and listen to music. He wanted to grow up to be a fireman. Or a scientist. He was not big on sports.

In his senior year at Charleston Catholic High School, the football coach sent him into the homecoming game during the fourth quarter. Harry tackled his own teammate, allowing the rivals to score a touchdown.

After high school, he studied economics at West Virginia University and also attended West Virginia State College. He dropped out one semester short of receiving his degree.

He lived alone and worked at odd jobs: volunteer work at a mental hospital, delivering telegrams, typing, waiting tables in restaurants, clerking at local stores, bookkeeping for an appliance repair department.

Then, in 1974, Harry Zain seized on the first of his many causes: abortion.

"The flame caught me," he said.

He was arrested several times for disturbing the peace during anti-abortion protests. He knelt in the snow for three hours in front of a church, holding a Bible and a dead fetus in a jar.

He made headlines in the local papers: Harry gets thrown out of church -- five times. . . anti-abortion zain RELEASED FROM JAIL. . . ZAIN LASHES OUT AT ROCKEFELLER.

"His dark eyes burn like the eyes of men who see Jesus on the wallpaper," a local columnist wrote of Harry Zain. "He acknowledges that people tend to leave the room when he enters them, but he has not permitted rebuffs to deflect him from the pursuit of what some would call obsessive concerns. Perhaps he is comforted by Shaw's observation that reasonable men do not advance civilization."

Says Don Marsh, editor of the Charleston Gazette, "Harry Zain is an eccentric. I think he's nutty. He's a zealot. He burns."

Marsh said he barred Zain from the newsroom after a series of unpleasant encounters. "I thought he was a nut, and I thought he was dangerous."

Then, Harry Zain took up his greatest cause: child bride-dom.

In 1977, his intensive lobbying efforts paid off when West Virginia State Sen. Si Galperin agreed to sponsor a bill that would lower the marrying age for girls from 16 to 12.

"Harry is quite a lobbyist," said Galperin, who opposed the idea but felt Zain should have a chance to be heard. "That bill almost got out of committee. Frankly, I was shocked. I couldn't believe anyone was serious about voting for it."

After working with Zain, Galperin said, "I don't imagine he has any close friends. He is the kind of person who's, well, not completely sane. There's something lurking back there."

George Zain, Harry's uncle, defends his nephew's zeal.

"He's not a kook," said the elder Zain, a south Charleston city councilman. "He may go about it uniquely, but he's never caused any problems. I think it's unique for anybody to fight a battle on their own.

"In fact," said Zain, pausing to reflect, "I think Harry's probably brilliant." Harry, Oh . . .

Meanwhile, back at the luncheonette, Harry Zain hasn't touched his hamburger platter. He wanted to order breakfast, he says, but it would have been too confusing. He orders two Cokes and rummages through his shopping bag on the seat beside him. He pulls out pieces of clothing, a thick wad of newspaper clippings, copies of letters to congressmen, a blue scrapbook with neatly pasted pictures of Milton and Shelley and a pocket-size packet of Kleenex tissues.

The world according to Zain:

"Elderly housing is really a form of communism."

To prove that point, Harry camped out one night in the snow back in Charleston. It was 18 degrees. At 4 a.m. shivering, he trudged over to the Heart-O-Town Motor Inn where he sat in the lobby for four hours before returning to his protest.

What, Harry Zain was asked by a newspaper during his first political campaign, can be done to improve the housing situation in West Virginia?

"If a man needs a house," Harry replied, "let him build it. If a girl, she must ask her brother; a widow might find her children when they've eaten their ham (but before they start Bingo); a Christian Church will receive orphans. Wherefore the government need fabricate neither houses, nor housing situations."

One year he took his bicycle and eight paperback Bibles to the sidewalk in front of Charleston High School where, during the students' lunch hour, he tried to convert them.

"They said I had been thrown off the property, but I hadn't," Harry says, referring to newspaper accounts of his noontime sermons.

He smiles nervously. The waitress hovers by the booth, asking him what's wrong with his lunch.

"Nothing," he says politely. "I'm not hungry."

"Well, that's the strangest thing I've ever seen," she mutters. "Why don't you take it and have it later?"

"I don't want to," he says.

"Well, really, you can just wrap it up and. . . ."

"All right," he snaps. His long white fingers are trembling. He is talking faster now.

"The people in this city are absolutely strange," he says. "They are sheep without a shepherd. They have no marriage in this city. They have, what's the word, orgies. They don't know how to live. They go home and have loud screaming and lewd talking."

Harry Zain says he doesn't mind living alone. "A man is very natural alone. Shelley says that. The poet, Shelley."

His parents want him to move back to Charleston, he says. But he's not leaving until his work is finished.

Does he honestly think his bill has a chance of becoming law? "Sure. There's plenty of hope," he says, anxious to get over to the Senate.

In the last three years he has come up with other causes: a bill making it grounds for divorce if a man forces his wife to work, a bill that would make it a crime to transact any business with a female of any age.

He breezes past the guard and heads for the steep marble steps of the Capitol. "I always take the steps. All the senators do."

He disappears inside, his black raincoat flapping like the wings of a crow.

The trouble with Harry, said one acquaintance, is he just doesn't know when to let go.