In the home stretch of his 1980 campaign, Rep. John LeBoutillier (R-N.Y.) lent $227,800 to his election committee. Without the loan, he has said, "I couldn't have won."

The wherewithal for a loan of such size is not apparent in the financial disclosure statements he has filed with the House of Representatives, as required by law. The statements listed assets of no more than $50,000 both nine months before and two months after he made the loan.

The election law lets a candidate lend or contribute unlimited personal funds to his campaign, and LeBoutillier says he got most of the $227,800 from a trust created after his father died in 1979. But the will provided for no direct money to him, and his half-brother, David, says no such sum went to John LeBoutillier from their father's estate. The estate had liquid assets of under $400,000.

In an interview in May, the congressman said the loan was proper. As a result of his father's death, he said, "A trust was created, and I benefited from that trust." Told that he is not named as a beneficiary of either of the two trusts created by the will, he said that the will does not reveal "what prearrangements there were on the trust, anything of that sort. You don't know the relationship between my mother and the brothers, and so forth."

New York law gives legal force to the trust arrangements spelled out in a will, but to no other arrangements or prearrangements concerning that trust. The father's will and estate papers are public documents.

LeBoutillier declined to grant a second interview. On June 14, written questions were submitted at his request, but he has not answered them.

The election law permits no campaign contributor other than the candidate to lend or give more than $1,000 each for the primary and the general election. Anything over $2,000 is a violation.

LeBoutillier was 27 when he became the youngest member of the House. Presidents Reagan and Nixon are among his fans, and persons close to them raised large sums for his campaign.

He has won publicity by insulting leaders of both political parties, calling them such names as "drunken bum," "scum," "skunk" and "wimp." He calls Congress "a joke," and acknowledges presidential ambitions. His 1978 book, "Harvard Hates America: The Odyssey of a Born-Again American," helped make him a hero to many Republicans.

He received a Harvard master's degree in business administration only five months before being elected, and had never held a job. His mother, Pamela Tower LeBoutillier, is a descendant of two of America's wealthiest families, the Vanderbilts and the Whitneys. She lives on a five-acre estate in Old Westbury, N.Y., a wealthy Long Island community.

The 1980 income that LeBoutillier reported to the House ethics committee was $7,790 from lecture fees and between $16,002 and $55,500 from dividends, interest and capital gains. He has never listed the $227,800 campaign loan as an asset, although his campaign committee owed him all but $8,680 as of March 31. Standard accounting procedures treat an outstanding loan as an asset.

LeBoutillier said he got about $30,000 of the $227,800 campaign loan by selling stocks. In late 1980 and 1981 he was asked repeatedly where he had gotten the remainder, and he gave consistent answers.

"It's just my own money left to me by father when he died a year ago of a heart attack," he told a constituent at a town meeting on Long Island. Newsday reported, "He said the loan represented most of a 'six-figure' inheritance he received upon the death of his father in 1979." In an unpublished portion of a Rolling Stone interview, he said, "And the rest of it was my inheritance from my father when he died the year before, and I got it last year."

David LeBoutillier disputed the congressman's accounts. "That was an error on his part, to say his father left it to him," he said. "He's leaving himself open to a complaint from the Federal Election Commission. He said it to fill in a square about where the money was coming from. He couldn't say, 'Someone just gave it to me' or 'I found it on the street.' "

David, a Trans World Airlines pilot, also said, "There's a lot of money in the family, directly or indirectly, and I think that's where it came from." He added, "The money is not coming out of the trusts, regardless of the statements that he's made." Based on what the congressman told him, and what he said he believes to be the fact, David LeBoutillier added, "I don't think he's misusing the trust."

Commission regulations, which define contributions to include loans made to influence federal elections, also say, "No person shall . . . make a contribution in the name of another, knowingly permit his or her name to be used to effect that contribution or knowingly accept a contribution made by one person in the name of another."

The congressman's mother is listed for a campaign contribution of $500. Reached by telephone, she said, "Oh, I really don't want to give an interview. It's really not my business to talk to the press. Sorry."

LeBoutillier's prolonged inaccessibility is a departure from his previous ready availability to reporters. A Wall Street Journal profile in February began, "Congressman John LeBoutillier came to Washington with his mouth wide open. He hasn't shut it since. That is the secret of his success."

His and David's father, Thomas LeBoutillier, a retired test pilot for Grumman Aircraft Corp., died in November, 1979, nearly two months after John became the unopposed GOP and Conservative Party candidate.

The will, which is in an open file in Surrogate's Court in Nassau County, directed that all of the adjusted gross estate of $731,251 go into two trusts for Thomas LeBoutillier's widow, who can draw on them whenever she wants. After her death, what is left in the trusts is to be shared equally by the four children of the father's two marriages, including John LeBoutillier.

LeBoutillier lent the money to his campaign in five parts over 13 days starting Oct. 16, 1980, six days before he recorded the initial loan installment of $60,000 and 19 days before the general election.

Campaign treasurer Lawrence R. Hertz, replying to a commission inquiry in a December, 1980, letter, said, "Let me state without qualification that the candidate, John LeBoutillier, used his own funds in the total amount of $227,800 . . . . "

Hertz, a certified public accountant, said he based this on "what was told to me by the candidate" and that LeBoutillier had transferred the money from his personal bank account to the committee bank account.

The $227,800 paid for a barrage of campaign television commercials that were widely believed to have been the decisive element in LeBoutillier's upset of veteran Democratic incumbent Lester L. Wolff. "If I hadn't had my own money," Esquire magazine quoted him as saying, "I couldn't have won."

President Reagan demonstrated his admiration for LeBoutillier by taking time out from his observance last Thanksgiving Day in Santa Barbara, Calif., to call the congressman while he was conducting a radio call-in talk show in New York City. "As a matter of fact, I've read your book," Reagan said warmly.

LeBoutillier became special in the eyes of Republicans by performing a prodigious feat of fund-raising while an undergraduate at Harvard. From his dormitory room in 1974, when he was 21, he raised more than $250,000 for an unsuccessful GOP challenge to Sen. George McGovern (D-S.D.).

In 1976 LeBoutillier ran Gerald R. Ford's New Jersey presidential campaign. In 1980, two members of Reagan's "kitchen cabinet," Justin Dart and Holmes Tuttle, helped him raise more than $30,000 for his campaign at a Los Angeles luncheon. In 1982, LeBoutillier has said, he will seek reelection, but from a revised district, the result of a reapportionment.