No one who knows George Vernon Hansen was surprised when the burly Idaho Republican turned up in Tehran this week amidst the turmoil and confusion in the siezure of the U.S. Embassy there.

Throughout his turbulent and controversial five terms in Congress, Hansen habitually has operated outside traditional channels, doing the unexpected and the unconventional.

His spur-of-the-moment decision to fly to Iran at his own expense on a one-man self-proclaimed "mission of mercy" to try to free the 49 American hostages is a natural product of Hansen's personal and political style.

The Iran trip is not Hansen's first foreign policy initiative. Last July, he and another conservative, Rep. Larry MacDonald (D-Ga.) flew to Nicaragua two weeks before President Anastasio Somoza's overthrow to tell the dictator that the United States stood behind him and that U.S. journalists had lied about and "distorted" his unpopularity. Earlier this year, Hansen waged an independant mail campaign to convince residents of the Panama Canal Zone that it was "not too late to save the canal," and urged them to support congressional attempts to impede passage of the Canal treaties.

At 49, the 6-foot-6 inch, 250-pound congressman has survived a guilty verdict in a campaign finance law prosecution, a federal judge's assessment that he was "stupid, but not evil," a fight with the Internal Revenue Service over charges that he filed late tax returns, selection to the "Dirty Dozen" environmental enemies list, and challenges from within his own party throughout a career that has repeatedly confounded observers of Idaho's political scene.

Hansen represents Idaho's Second Congressional District, which reaches from the state capital of Boise in the west to the Montana and Wyoming borders in the east.

It is a rural district, with potato and sugar beet farms in the irrigated valleys and cattle ranches on the high desert plateaus. The district also is home to the largest Mormon population outside of Utah.

Out of such a background comes Hansen -- himself a devout Mormon and so solid a conservative that his voting record has won a zero rating from liberal Americans for Democratic Action and 100 percent approval from the conservative Americans for Constitutional Action.

Hansen, a former life insurance salesman and once the youngest mayor in the state, upset a two-term Democratic incumbent in 1964 to win his first term in Congress.

After easily winning reelection in 1966, he ignored the pleas of Idaho Republican leaders and ran against Sen. Frank Church (D-Idaho) in 1968.

Hansen lost to Church, then lost a primary race for the Senate in 1972.

In 1974, he challenged incumbent Rep. Orval Hansen (no relation) in the Republican primary, and shocked political observers by defeating his well-respected, but moderate, opponent.

That campaign, the first to be run under new and tougher federal campaign finance reporting laws, got Hansen in trouble. He pleaded guilty to two misdemeanor charges of filing late and incomplete campaign financial reports, and became the first sitting congressman in 19 years to be sentenced to prison.

But U.S. District Court Judge George Hart in 1975 suspended Hansen's prison sentence and slapped him instead with a $2,000 fine, calling him "stupid, but not evil."

In 1976, controversy erupted over reports that he had been late in filing his personal income tax return for eight different reporting years between 1962 and 1975. He refused to confirm or deny the charges, and no legal action was taken against him.

Hansen squeaked through the 1976 election with a 1.2 percentage-point margin over an aggressive young Democratic challenger, but in 1978 he handily whipped the same opponent, 57 to 43 percent.

Hansen had been restored to political good health by one of his "outside the system" political crusades: A four-year-long effort to loosen restrictions on small businesses regulated by the Occupational Safety and Health Administration.

In 1975, a Pocatello, Idaho, electrical contractor named Bill Barlow refused to let OSHA inspectors enter his shop without a search warrant. This was the case Hansen had been looking for.

He made his Washington office a clearinghouse for complaints of OSHA abuses and conducted another nationwide fund-raising appeal to finance his fight against the agency.

When the U.S. Supreme Court three years later ruled warrantless searches unconstitutional Hansen had achieved his greatest political victory. It cemented his postion with the Second District's conservative voters and paved the way for his reelection last year. CAPTION: Picture, REP. GEORGE HANSEN . . . sought to see hostages