He is so familiar, this man Ronald Wilson Reagan, who has played so many roles for so many years on the American scene.

The Secret Service calls him "Rawhide." His imagemakers have created posters that show his lopsided grin and crinkly gaze peering out from under a white cowboy hat.

Rugged, comfortable, saddleworn, a 20th century cowboy.

Ronald Reagan, the man of so many seasons: sportscaster, actor, pitchman (for General Electric refrigerators and 20 Mule Team Borax), governor, Mr. Conservative and, for much of the last dozen years, candidate for president.

The image, like all political images, is partly fact, mostly fancy. It bears only passing resemblance to the man who has spent much of the last quarter century on the rubber-chicken circuit, with a well-worn set of 3x5 cards, extolling conservative causes before groups like the Turkey Owners Association of America.

Reagan the politician is first and foremost a symbol of that same conservatism. His nomination tonight was an affirmation that the same tides that sent Barry Goldwater drifting hopelessly to sea in 1964 now form a main current of American politics. "It's not so much he [Reagan] has changed as we've changed," William Agee, chairman of the Bendix Corp., said a few weeks ago."

That same realization -- however overstated -- permeated Joe Louis Arena this week. When an aging and slightly infirm Goldwater came to the podium Tuesday night, an ambitious border state officeholder who has spent much of his career battling Goldwater forces jumped to his feet in applause. "A fella could get hurt not cheering for Barry Goldwater in this crowd," he said sheepishly. "My mom didn't raise no fool children."

Asked how he could feel comfortable in a party that had just adopted a platform far more conservative than he is, Iowa's moderate Gov. Bob Ray said, "It sure feels good being with a winner."

A 30-minute television spot done by Reagan for Goldwater in the last, hopeless days of the 1964 race brought the Californian into politics. It was a humdinger of a show, containing many of the elements that make up "The Speech" that still delights Reagan's audiences. He railed against big government, the communist menace and creeping socialism. He called urban renewal "an assault on freedom," social security "a welfare program."

If that appeal was a successful match of show business and politics, Reagan's nomination tonight was the ultimate blending of the two. Politics has become show business, show business has become politics.

Never before has an actor been nominated for president. Never before have politics and show business been so synonymous.

Many in the Reagan camp resent dwelling on Reagan's days as a movie actor. It diminishes his eight-year term as governor of California, the nation's most populous state, and his years as a compelling spokesman for conservative causes, they insist.

But it was through movies and television that Reagan first came to prominence. If he had not been a Hollywood actor he might never have been in a position to become his party's nominee.

Reagan's roots, like those of many presidential nominees, and political philosophy are a product of smalltown mid-America. In his case it was the small town of Tampico and the Illinois countryside of the 1920's, a time of Fourth of July parades, church-going, Rotary Club meetings, flag-waving and unswerving optimism.

He was born Feb. 6, 1911, in a four-room flat on Tampico's Main Street, the second shot of Jack and Nelle Reagan. His shoe-salesman father, a hard-drinking Irish-Catholic, was an outspoken Democrat in a Republian area.

"Dutch," a nickname he preferred because he thought "Ronnie" sissified, was an all-American boy, more interested in football than books. The pictures of him in his Dixon, Ill., high school yearbook show him looking remarkably like the 69-year-old politician he is today. There is the same lean, broad-shouldered build, the same appealing twinkle in the eyes.

He worked his way through Eureka College, 60 miles from his home, by washing dishes and working as a lifeguard in the summer. He was a big man on a small campus, a football player, fraternity man (Tau Kappa Epsilon) and actor in school plays.

Reagan has traveled a long way since graduating from Eureka in 1932 with a degree in sociology and economics. Although he has changed from a New Deal Democrat to a conservative Republican his view of life has remained constant.

"There are simple answers, just not easy ones," he is fond of saying.

Reagan's career, has all the elements of a Hollywood script. For five years, he was a sportscaster, most notably on WHO in Des Moines, one of the largest radio stations in the Midwest, and he broadcast Big 10 football and Chicago Cubs baseball games. At age 26, he took a screen test. The casting director at Warner Brothers saw him as "another Robert Taylor" and signed him to a six-month contract.

Over the next 27 years, Reagan made 54 movies, including several forgettable B-grade flicks such as "Bedtime for Bonzo," in which he played opposite a chimp to the everlasting amusement of reporters assigned to his campaigns.

Reagan never was nominated for an Oscar, nor was he ever big at the box office. But he was a good, journeyman actor. He frequently has complained that he would have been better off if his career "hadn't been interrupted" by World War II. He spent the war narrating training movies.

Reagan now describes himself a "B-Grade Errol Flynn" who was most offten cast in "Mr. Nice Guy" roles in which he always got the girl.He met his first wife, actress Jane Wyman, while filming the movie "Brother Rat," and his second, Nancy Davis, while doing "Hellcats of the Navy."

As president of the Screen Actors Guild and a liberal Democrat, Reagan was twice urged to run for political office. But it was not until 1966, when he ran for governor and beat Gov. Edmund G. (Pat) Brown by 1 million votes, that he formally entered politics.

But that time, he was an archconservative Republican. Some people speculate that the transformation was due to his association with General Electric executives, for whom he worked during the 1950s, or wealthy California businessmen who befriended him. Others say he was influenced heavily by his wife, Nancy, and father-in-law, Dr. Loyal Davis, a Chicago neurosurgeon of outspoken beliefs.

The way Reagan tells it, his term in Sacramento was the golden era of government in America. He regales audiences with stories of rooting out waste, reforming welfare, restoring a bankrupted government and rebating state surpluses.

Reagan is remembered with respect and even some affection as a surprisingly reasonable governor. But nearly every major state tax rose substantially during Reagan's eight years as governor. He signed the nation's most liberal abortion law. And he was regarded as a 9-to-5 chief executive.

But reality seldom catches up with rhetoric in politics, and almost from the moment he became governor, Reagan -- not content with a B-grade part -- began looking for a national role.

Tonight he has the lead in the biggest drame of all.