When Jesse Unruh arrived in Sacramento 32 years ago as an overweight, underpaid state assemblyman, he became part of a legislature that was largely of the lobbyists, by the lobbyists and for the lobbyists.

The history books will say that Unruh, who died of cancer Tuesday in his California home at the age of 64, took money from these lobbyists and used it to elect legislators who made him, as speaker of the Assembly, the most powerful politician in California. The historians will also say that Unruh used this power to transform a supine and dependent legislative body into one that had a decent respect for the people and sufficient resources to represent them. They will say that the Unruh era was a time when the legislature initiated action to help the needy, protect consumers, advance civil rights and save some of California's magnificent parklands before developers could destroy them.

During the Unruh years, these achievements were overshadowed by the forceful personality and gargantuan appetites of "Big Daddy," a nickname given him by his friends and hurled back in his face by his enemies.

He was called "Big Daddy" because of his supposed resemblance to the domineering southern father played by Burl Ives in the film version of "Cat on a Hot Tin Roof." But Unruh really was more Broderick Crawford than Ives, the Crawford who portrays a thinly disguised Huey Long in "All the King's Men" and rallies the rural dispossessed to his banner by calling them "hicks" and promising them a taste of the power they have never had.

When Unruh went to the legislature, he was a real hick from the cotton fields of Swenson, Tex., by way of the Navy and a GI Bill of Rights education at the University of Southern California. He had been dirt poor, and he once said that he never wore socks before he was 12 but that no one could tell because his feet were so dirty.

" . . . They live in a steady shame and insult of discomforts, insecurities and, inferiorities, piecing these together into whatever semblance of comfortable living they can," James Agee wrote of similar sharecroppers. This is what Unruh's life was like as a boy and, in some inner recess, what it must always have been like. After he became, at 39, the youngest speaker of the Assembly in California's history, he told a friend, "I'm still not sure I'm not going to wake up some day and be on a small farm out there in Texas."

Perhaps because he knew what it was like to be truly powerless, Unruh had a keener appreciation of power than more sheltered politicians. "He was the premier politician in the state because he knew the issues and understood the uses of power," said Stuart K. Spencer, a longtime Republican adversary and friend. "He used power to advance the causes he believed in. He was very honest and didn't go sneaking around when he wanted money like some politicians do. But the key was that he was willing to use the power once he acquired it."

Unruh's Democratic candidates and Spencer's Republican candidates competed for the legislature in campaigns of brutal intensity and misrepresentation. Afterward, they would drink together and tell stories about what they had done to each other. Unruh did not avoid his adversaries, and he valued most those who shared his understanding that politics was both a noble calling and a dirty business.

Unruh was not afraid to get his hands dirty. He despised those who disdained political detail or soared above the petty and sometimes ugly struggles by which he remade the State Assembly. Unruh boasted too much and ate too much and, for a long time, drank too much. But he did not shrink from the reality of his faults or his virtues.

Instructing freshman assemblymen on how legislators were supposed to behave in lobby-ridden Sacramento, Unruh would say, "If you can't eat their food, drink their booze, screw their women and then vote against them, you have no business being up here." This doctrine formed the core of Unruh's political theology. He knew that the lobbyists were an eternal fact of life. He believed that the way to deal with them was to accept this fact and use their resources to advance his own agenda.

He did not deal as successfully with Ronald Reagan as he had with the lobbyists. Unruh was too proud of his political skills to appreciate the contempt which many Americans hold for politicians as a class. Gov. Reagan, who did not know the contents of his own legislative program, understood and shared this prejudice and exploited it at Unruh's expense.

But it is also true that Unruh, who was at bottom an unrelenting, populist Democrat with a personal understanding of poverty, gave Reagan a tougher political race than any other Democrat has before or since. You can look it up, as Casey Stengel would have said. Without money or organization or an attractive television personality, Unruh nonetheless came much closer to defeating Reagan at the polls than did Gov. Edmund G. (Pat) Brown, President Jimmy Carter or Vice President Walter F. Mondale.

After Unruh lost to Reagan in 1970, his political life went downhill. He was strong enough to accept defeat, but he was unable to deal with powerlessness and being out of the legislature. As an elder statesman, he was a bust.

Unruh subsequently was elected state treasurer, a job whose requirements he mastered within minutes and which gave him time and freedom. But his home was no longer in the future, and he spent the rest of his life recalling the glory days when he had been "Big Daddy," the powerful speaker of the Assembly.

He had a right to do that, a right to feel pride in his accomplishments. He did something that no else has ever done. He went to California as a Texas hick and remade its corrupt and backward-looking legislature into a modern instrument of democracy. This is not a small thing.