The youngest member of Congress doesn't believe the unwritten rule that says freshman congressmen are to be seen, not heard. In fact, the youngest member of Congress already dislikes a lot of what he's seen on Capitol Hill.

The House Speaker, for example.

"Tip O'Neill personifies everything the public hates about politics in America," says Rep. John LeBoutellier, the 27-year-old Republican Wunderkind who last fall confounded the smart money by capturing the Long Island, N.Y., seat held by Democrat Lester Wolff. "Tip's old-fashioned, behind-closed-doors, semi-ethical politics . . . that's just what the public can't stand, and that's how he runs things."

LeBoutellier (who completely dismisses Jimmy Carter as "a complete birdbrain") is equally underwhelmed by some of O'Neill's colleagues.

"I'm really a little appalled by how slowly they do things up here," he says. "You'd think that after the last election, they'd all be working hard. But no. After only four and a half weeks, they deserve a week off."

If his sarcasm over Congress' George Washington's birthday recess irritates, LeBoutellier couldn't care less. He is a bright young bachelor who says his constituents elected him not to be nice but to change Washington's wicked ways. His staffers are young -- only two of his nine Washington employes are older than he -- and all worked for no pay to elect him. They were called the Lone Ranger Gang on Long Island two years ago when LeBoutillier was a dark horse. But the kid campaigner raised a formidable war chest from Republicans around the country, knocked on doors, spent three times what Wolff did, and fooled the pollsters by winning with a 12,000 vote margin.

LeBoutellier, the son of a test pilot, grew up in a wealthy home. His mother descends from the Whitney family, as in Pratt & Whitney, the Whitney Museum, and philanthropic organizations too numerous to list. After Brooks School in North Andover, Mass., LeBoutellier was graduated from Harvard (A.B. in history, magna cum laude, '76; M.B.A., '79).

It was at Harvard that he became a Republican. In a 1978 book, Why Harvard Hates America, LeBoutillier wrote that by his sophomore year he'd decided his liberal professors and radical fellow students were hypocritical elitists whose concern for the less fortunate ended when (in the students' cases) they landed high-paying jobs on Wall Street or (in the professors' cases) the checks from their wives' trust funds arrived.

In 1973 LeBoutillier read about an ex-POW, Republican Leo Thorsness, who was challenging George McGovern's reelection in South Dakota. Without meeting Thorsness, LeBoutillier began fund-raising, eventually collecting more than $250,000. Though Thorsness lost, LeBoutillier's labors later endeared him to, among others, Ronald Reagan's good friend, Justin Dart.

"It came to my attention that John raised a pot full of money for the senatorial opposition of our favorite S.O.B. in South Dakota," Dart said recently. "And he did it from a dormitory room at Harvard. I thought a guy who had that much get up and gumption and go would be damn well worth supporting."

Dart and another member of Reagan's kitchen cabinet, auto dealer Holmes Tuttle, helped LeBoutillier raise more than $30,000 at a Los Angeles luncheon last year.

Today Rep. LeBoutillier has a seat on the House Foreign Affairs Committee and a headful of ideas about shaking up government. He'd like to kick PLO representatives out of the U.S. He says his constituents want an immediate cut in government spending along with a tax cut. He thinks a Democratic House will thwart Reagan's goals, so Tip O'Neill will have to go in 1982.

Meanwhile, LeBoutillier wears a button that identifies him as a congressman so Capitol Hill police won't bar him from entering hearing rooms. cOne guard saw him posing for a photographer in a jogging suit on the Capitol steps and told him to get lost. Another calls him "El Youngo." But LeBoutillier revels in his youth, vowing to quit the day he becomes the kind of pot-bellied legislatgor he says the House is too full of.

"I wish we'd get going," he says. "They really could get a year's worth of work done in three or four months. But they love to stretch it out and make it a full-time job."