Jim Abourezk was always the iconoclast: a champion of Palestinians and American Indians, a caustic foe of big oil companies and a rare defector from the most exclusive club in town, having quit the U.S. Senate two years ago to practice law.

Now this outspoken South Dakota lawyer is in the headlines again, this time as the attorney for the Ayatollah Ruhollah Komenini's Islamic Republic of Iran.

He isn't shamed, but he isn't exactly boasting about representing a government that has imprisoned 50 Americans for 11 weeks and caused a crisis in U.S. foreign relations. "If I looked just for popular clients, then I should be a politician, not a lawyer," says Abourezk, more than a little defensively.

Ask him about the hostages and this one-time garrulous headline-hunter clams up. "I don't want to divulge my private feelings," he says. "If I had to give a personal opinion on all my clients, I wouldn't have any clients."

Abourezk gets angry. "Am I required to express outrage over anything? I'm not in the Senate anymore. Am I required to express anything to the newspapers? I don't want any press coverage."

When a former U.S senator sues Mohammed Reza Pahlavi, the deposed shaw of Iran, and his wife, Farrah, for $56.6 billion, on behalf of a new revolutionary government, press coverage is hard to avoid.

Abourezk's seven-lawyer firm also oversees lawsuits involving 100 to 200 companies that once did business with the shaw and now find themselves caught in the transition. The new government says it will "pay honorable debts" Abourzek says, but the Carter administration has frozen Iran's assets here.

The quiet downtown offices of Abourzek, Shack & Mendenhall look like those of any other Washington law firm: English fox hunting prints on the walls, soft carpets on the floor and demure secretaries answering the phone.

Abourezk, a stocky man dressed in an open-necked ultrasuede shirt, ushers a visitor into an office with two backgammon boards open on the table and large color blowups on the wall of Abourezk and Jimmy Carter, Abourezk and Fidel Castro.

"My head hasn't changed," insisted the man who was once known as the Senate's feistiest liberal. "I'm now a private servant. When I was in politics I was representing the people of South Dakota and the public at large. Now I have a different constituency and I do different things to represent them."

One of those things was a quiet attempt to negotiate the freedom of the American hostages. In late November, the former Democratic senator met twice with Abol Hassan Bani Sadr, then Iran's foreign minister. Abourezk suggested a congressional airing of Iran's grievances -- a proposal later nixed by Majority Leader Robert F. Byrd (W.Va.).

Abourezk won't talk about those dealings today except to say, "I tried to ease the psychological climate about Americans."

To help with Iran's complex litigation Abourezk retained dozens of other law firms in cities across the country, including New York firm of Paul O'dwyer, the formerNew York City Council president.

At first, Abourezk said, "The Wall Street firms were hiring to defend the bank cases were squeamish about representing Iran. They said their other clients would object. So I got a letter from the State Department saying that, pursuant to U.S. policy, Iran should be represented in U.S. lawsuits."

Abourezk accompanied American journalists to Iran a few weeks ago to introduce them to Iranian banking officials and to help them obtain documents illuminating the shah's financial dealings.

Abourezk's firm also oversees legal work for thousands of Iranian students here who have problems with immigration officials or who face harassment at school.

It was through some students that the former senator was able to land the Iranian account in the first place. As he tells it, several hundred students were demonstrating against the shah in front of the Iranian Embassy here last winter. The police arrived and began to arrest students. One of the leaders, having heard of Abourezk through a friend, called him and asked him to represent them.

"By the time I arrived at the scene," Abourezk recalls, "the police had arrested about 65 of them. I negotiated with the police and they agreed to stop the arrests. I stayed up until two in the morning getting them out of jail." After the revolutionary regime took power, he said, "the people running the embassy came down and asked me to handle their legal work."

It is a long road from Rapid City to Washington, from immigrant Lebanese peddler's son to superlawyer, but the 48-year-old Abourezk seems to have traveled it with wit and realative ease.

He enjoys handing out official-looking business cards that read, "Hammurabi, Moses, Justinian, Blackstone & Abourezk." A joke, to be sure, but with a serious message: James George Abourezk has made it.

That didn't always seem certain. Abourezk, born on South Dakota's Rosebud Sioux Indian reservation, served four years in the Navy and then worked his way through the South Dakota School of Mines by teaching judo.

He has been a farmer, a used-car dealer, a surveyor and a bartender. He has sold groceries on the road, owned a nightclub and dealt blackjack at the American Legion.

After a year as an engineer in California, he returned to South Dakota with his wife and three children, went to law school and set up practice in Rapid City in 1966. In 1970, Abourezk was elected to Congress, where he served a term each in the House and the Senate.

While in office, Abourezk says he went to only one lavish caviar-strewn parties at the Iranian Embassy "just to see what it was like." He may have signed a few petitions against the shaw, he said, but otherwise had virtually no involvement with Iranian affairs.

Instead, Abourezk, the only Abab-American in the Senate, was known as a defender of Arab causes and a controversial critic of what he called the "Israeli lobby." Lester Kinsolving, the conservative radio commentator, delighted in calling him "the senator from Saudia Dakota," a label that reportedly infuriated him.

Abourezk alienated his collegues with such ploys as an all-night, unsuccessful filibuster against attempts to deregulate the price of natural gas. He advocated breaking up large oil companies.

Restless and possbily frustrated by his lack of legistative success, he left the Senate to practice law and to devote more time to his family.

Law practice, he said, has given him "independence. I have my own private family life. There is not so much intrusion as when I was in politics. I work any hours I want. I travel when I feel like it, and my wife travels with me. We can afford it now."

Just last week, Abourezk returned from a vacation in Hawaii, and, in the last few months, he has traveled to Florida, spent several weeks in the Utah mountains and visited Tibet to take photographs, a favorite hobby.

Abourezk's partners, Gregory Mendenhall and Thomas G. Slack Jr., an old friend from the Robert F. Kennedypresidential campaign, do much of the legal work. Shack is handling the suit against the shaw, which alleges that the Pahlavis diverted at least $20 billion in Iranian government funds to their own use.

"I don't do legal research," Abourezk said, "I have lawyers working for me who do that. I help run the law firm and make decisions." He also represents several Middle Eastern clients, American companies in the Middle East and several Indian tribes.

Abourezk said he does not need to register as a foreign agent with the State Department, because he conducts only commercial litigation which is exempt from registration requirements. He declined to discuss his fees.

Does he regret leaving the Senate? "For the long term benefit of civilization," he relies, "it would be better if I were to represent the public. But it's a matter of how I want to live personally."