Trying out new self-characterizations on the campaign trail, Ronald Reagan sometimes describes himself as a "Main Street Republican."

In the context of the 1980 presidential campaign, the phrase is intended to show that Reagan is a grass-roots sort of Republican, not a boardroom candidate, an Ivy Leaguer or a right-winger.

But in Reagan's case, the phrase has another meaning. Like all people, he is the product of his time, and region, his experience and his culture.Reagan's time, region and original culture were small-town Illinois, the quintessential Main Street celebrated in Middle America and satirized by Sinclair Lewis' famous novel of the same name.

"Main Street is the climax of civilization," Lewis wrote in the preface to his novel, which appeared in 1920, when Reagan was 9 years old, and already a quick study and prodigious memorizer.

Lewis meant these words sardonically, but Reagan would be content with them as literal truths. In interviews with biographers, and in his own ghosted autobiography, "Where's the Rest of Me?", Reagan has described his early years in a succession of Illinois small towns as an ideal existence. Looking back on the early boyhood in his autobiography, Reagan calls it "a rare Huck Finn-Tom Sawyer idyll."

"Reagan was shaped by the small towns of the Midwest, and that explains in large part the simple moral and conservative approach he brought to public life," writes early biographer Bill Boyarsky. "Where Lewis satirized the Midwest communities, Reagan glorifies them. He enthusiastically accepts the values that Lewis criticized. As a result, he is deeply respectful of business, determinedly conservative; mistrusting of change; unintellectual and slightly suspicious of higher education . . . convinced that, as his father said, 'All men were created equal and man's own ambition determines what happens to him the rest of his life.'"

Reagan's father was John Edward Reagan, called Jack, a gregarious, hard-drinking Irish-American who worked as a clerk in the Pitney General Store in Tampico. Ronald Reagan was born in a five-room flat above the store on Feb. 6, 1911, and for the first nine years of his life, his family lived in an itinerant procession through Illinois cities and towns: Chicago, Galesburg, Monmouth, Tampico, and finally Dixon, the place Reagan still calls his hometown and where he lived until he was 21.

Reagans' mother, Nelle Wilson Reagan, was considered a do-gooder in her day and she would be thought of as one now. She was a lifelong member of the Christian Church who practiced what she preached, and both Reagan and his older brother, Neil, remember her helping the needy and finding jobs and lodging, sometimes in the Reagan home, for released convicts.

Ronald Reagan's retentiveness and early reading skills must have been a delight to his mother, who encouraged him to read newspapers aloud to her friends. Reagan still recalls reading an account of the Preparedness Day bombing in San Francisco on July 22, 1916, when he was 5 years old.

Reagan's autobiography, which describes both his boyhood and the equally shaping experience of Hollywood that would come later, tells of a happy, open, unprosperous midwestern family of the 1920s which in some ways was avant-garde for Dixon.

The boys, for instance, called their parents by their first names, and Neil and Ronald were "Moon" and "Dutch" to their parents and friends. The Reagans also were the town's Democrats in a place devotedly Republican. Both Jack and Nelle appealed to the imagination of their children by participating in amateur theatricals. The dark cloud of the family was Jack's drinking.

"I was 11 years old the first time I came home to find my father flat on his back on the front porch and no one there to lend a hand but me. He was drunk, dead to the world," Reagan writes.

"I bent over him, smelling the sharp odor of whiskey from the speakeasy. I got a fistful of his overcoat. Opening the door, I managed to drag him inside and get him to bed. In a few days he was the bluff, hearty man I knew and loved and will always remember," he adds.

The adult Ronald Reagan is a tolerant man, and he gives credit for this to his Catholic father. In his autobiography, Reagan relates how his father, then a traveling shoe salesman, was told by a small-town hotel clerk that he would appreciate the hotel's accommodations because Jews weren't permitted.

"I'm a Catholic," Reagan quotes his father as saying, "and if it's come to the point where you won't take Jews, you won't take me, either." Jack Reagan left the hotel, spent a cold winter night in his car, and became ill.

When a reporter recently asked Reagan to name the single-most important influence on his life, he quickly replied, "the Depression." The Depression cost his father a partnership in a Dixon shoe store he had opened with borrowed money. It sent his mother to work in a dress shop, for $14 a week. Reagan, who was working his way through the tiny college of Eureka, tells in "Where's the Rest of Me?" how he sent $50 home to his mother without his father's knowledge so that the family could continue to get credit at the grocery store.

The occasion that prompted that contribution has been told by Reagan hundreds of times, including the Nov. 16, 1979, speech in which he declared his presidential candidacy. The two Reagan brothers were back from college on Christmas Eve, 1931, when a special delivery letter arrived for their father. Jack Reagan had been hoping for a bonus. Instead he received a "blue slip" telling him that he was fired.

As an actor, Reagan can cry on cue -- and he's nearly in tears or close to it when he tells this story. Jack Reagan, out of work in the depths of the Depression, became dependent on government. He wound up with a patronage job in the Roosevelt administration, distributing relief to others in Dixon.

The Depression was a shaping event in Reagan's life in many ways. Like many survivors of that time, he emerged with strong economic motivation and the desire to provide a better material life for his family. He also became an ardent admirer of Franklin Delano Roosevelt, whose "fireside chats" on the radio were to provide the inspiration and some of the cadences for Reagan's own televised appeals to Californias 45 years later.

Though he stands opposed to much of the New Deal legacy, in part because of his experiences in Hollywood, Reagan to this day reflects the Roosevelt influence. The Democratic Party is to him just that, not the "Democrat" Party it has become for many western and southern Republicans. Roosevelt, Reagan said quietly in an airplane interview earlier this month, "was a great war leader."

Throughout his public career, Reagan has always quoted from Roosevelt. "You and I have a rendezvous with destiny," Reagan said in concluding the celebrated nationally televised speech for Barry Goldwater that launched Reagan's political career in 1964.

It was a variation of what Roosevelt said on June 27, 1936, when he accepted the Democratic nomination for president with the words, "This generation of Americans has a rendezvous with destiny."

That rendezvous, somewhat transformed, is still scheduled, if one accepts Reagan's declaration of candidacy for the 1980 campaign. He said then that "a troubled and afflicted mankind looks to us, pleading for us to uphold our rendezvous with destiny; [pleading] that we will uphold the principles of self-reliance, self-discipline, morality and -- above all -- responsible liberty for every individual . . ."

Reagan remembers hearing the original version and being thrilled by it. He was then 25-year-old Dutch Reagan, broadcasting for WHO in Des Moines where he quickly became one of the best-known sportscasters in the Midwest.

Already, Reagan was an inveterate speaker who liked the sound of his voice and the response of his audience. While working at WHO he would sometimes give talks to young people, interspersing sports stories with admonitions about drinking and smoking.

Perhaps there is no modern political autobiography that is as relentlessly cheerful and unintellectual as Reagan's. He is the perennial optimist whose fondest recollections are of playing seemingly endless football games and of a summer of lifeguarding when he rescued 77 people. At Eureka he led a student strike that restored Depression-cut classes and cost the college president his job.

By his own account, Reagan was an indifferent student whose photographic memory made it easy for him to devote a minimum of time to studies and to concentrate on playing guard for the Eureka college football team. He also liked politics, theatricals, girls. His brother remembers that in preparation for a radio career, he spent hours listening to sports broadcasts and to Roosevelt.

The other great shaping event in Reagan's life was Hollywood. He had been interested in acting from boyhood, and in 1937 when broadcaster Reagan accompanied the Chicago Cubs to Catalina for Spring training, a friend arranged a screen test for him with Warner Brothers. Reagan passed with flying colors.

Even today, Reagan still bristles at any suggestion that he proved a less than competent actor. And the reviews of his better pictures, written before he became a political figure, support Reagan's high view of his acting proficiency, rather than the sneers of his critics.

Starting out on low budget pictures where his quick retention of a script was an enormous asset, Reagan advanced to the role he remembers as "the Errol Flynn of the B's." But he won critical acclaim for his performances in "Brother Rat" (where Eddie Albert made his debut and where Reagan met first wife Jane Wyman), in "Dark Victory" (with Humphrey Bogart), and especially in "King's Row," where the cast included Claude Rains, Robert Cummings and Charles Coburn.

"In King's Row," a story of a small southern town that was more malevolent than Dixon, Reagan portrayed Drake McHugh, a playboy whose legs are amputated by sadistic surgeon Coburn as revenge for the courting of his daughter.

"Where's the rest of me?" yells McHugh, coming to without his legs and uttering the most famous line (and the title of his autobiography) in what Reagan considers his best picture. The critics thought so, too. Typical of the reviews as Commonweal's, which praised Reagan for "a splendid performance."

But Reagan never really got his movie career on track after World War II, which he spent making training films with an Army Air Corps unit in Hollywood.

After the war, Reagan's movie career was on the skids, along with his marriage to Wyman, who won a divorce after telling a court that Reagan spent too much time on Screen Actors Guild business and not enough time with her. Reagan was by now playing in films like the 1951 nonclassic "Bedtime for Bonzo" in which the hero is a chimpanzee.

By that time Reagan had established what was, in effect, a new career.

As leader of the Screen Actors Guild and six times its president, Reagan had become embroiled in the economic and emotional issues that shook Hollywood after the war.

If Main Street represented the climax of American civilization in the 1920s, Hollywood was at the time the undisputed capital of American mass culture. Sensational accusations that the industry was honeycombed with communists, disclosures that a key union was operated by gangsters, the emergence of foreign films as a major competitor, and taxation-induced "runaway" of American studios to other countries -- all these were front-page stories at the time.

Reagan was in the midst of these battles. During the communist-hunting days which Hollywood now recalls with embarrassment and some shame, Reagan opposed communists but also disputed the basic thesis of the House Committee on Un-American Activities in these words: "I do not believe the communists have ever at any time been able to use the motion picture screen as a sounding board for their philosophy or ideology."

Reagan fully pleased neither side with his stand. What no one seemed to have noticed at the time was that he emerged from a battle, which tarnished almost every participant, as an effective and adroit political leader who kept his union intact.

Reagan's personal life and political views were now changing. In 1952 he married Nancy Davis, adopted daughter of conservative wealthy Chicago surgeon, Loyal Davis. In 1954 he became host for "General Electric Theater," a new half-hour television series sponsored by GE.

Reagan was the sole recommendation of the late Taft Schreiver for the $125,000-a-year job at GE. The contract, which might be said to have launched Reagan's political career, gave him an opportunity to be seen each week on television, and to talk to GE employes and executives all over the country.

While some old Hollywood friends ascribe Reagan's increasing conservatism of this period to Nancy, it is probable that General Electric had much more to do with it than she did. Reagan and his friends were in higher tax brackets, and Reagan's business-minded audiences were concerned about taxation and government regulations.

Because of family loyalties, and the influence of the Depression, Reagan had remained a Democrat longer than most of his Hollywood friends. Most of the social friends of the Reagans were Republicans by now. Reagan had voted for Roosevelt four times and for Harry Truman for president in 1948. He considered himself a New Dealer and thought that Roosevelt had saved capitalism.

But he was on his way to becoming a millionaire, taxes were beginning to hurt, and Reagan was beginning to turn against the government that his idol Roosevelt had created during the Depression.

At the outset, Reagan's message had been patriotic, anti-communist, pro-Hollywood. GE Board Chairman Ralph Cordiner suggested to Reagan that, "you work out a philosophy for yourself." Increasingly, that philosophy became pro-business, anti-government conservatism.

Reagan, a Democrat who had supported Helen Gahagan Douglas against Richard M. Nixon for the U.S. Senate in 1950 became a Democrat for Nixon in 1960. Two years later, when Reagan was supporting Nixon in his race for governor of California, a woman in the audience asked Reagan whether he was a registered Republican. Reagan said he wasn't, and the woman, a volunteer register, signed him up for the GOP on the spot.

Reagan is a person who learns by doing, a practical man, whose strength is as a popularizer, not an original thinker. He tends to see most issues in terms of his own experience.

When Reagan wants to understand the effect of high tax rates on productivity, he invariably draws upon his Hollywood experience.

When Reagan wants to understand a social issue, such as race relations, he retreats to a fragment of a movie where a black corpsman in the segregated World War II U.S. Navy emerges on the deck of a burning ship. Cradling a machine gun in his hands, "which is not an easy thing to do," the corpsman starts firing at Japanese planes. As Reagan explained it to a baffled press corps during the 1976 campaign, it was this event rather than President Truman's postwar executive order that ended segregation in the armed forces.

Reagan also remembers a race riot that started at a card game in Dixon. In its ugly aftermath, whites advanced upon the black section of town and hurled frightened black children on to freight-laden box cars which carried them hundreds of miles from their homes.

Reagan is no bigot. As governor, he named more minority persons to state government posts than any of his predecessors. But he does not think that government has a responsibility to help minorities as minorities and he said during the 1968 urban disorders: "The greatest proof of how far we've advanced in race relations is that the white community hasn't lifted its hand against the Negro."

This view would probably have been shared by the many citizens of Main street, the selective crucible in which Reagan's basic attitudes were formed. Reagan still lives, it would seem, in a world where businessmen care for their customers, local government looks after its own community, people are good to one another, and the federal government stands up for American citizens abroad.

For Reagan, this year's likely Republican nominee in the nuclear age, the basic verities of his youth remain the guiding principle of his politics.

He is, in his own words and without exaggeration, "a Main Street Republican."