In a remote cabin on the Pine River in northern Michigan, an obscure congressman spent last week preparing a speech that he calls "a ticket to fame or oblivion."

He is Guy Vander Jagt, chosen to give the keynote speech at the Republicans National Convention. His choice was surprise to most.

No one questioned his oratorial ability. Vander Jagt is a ex-preacher and ex-TV anchorman, a genuine ham who can make a speech about a sewer project in Muskegon sound like the Gettysburg Address.

No one questioned his credentials as a Republican. He is a seven-term congressman, a member of the House Ways and Means Committee, and a contender for the party's top leadership spot in the House -- perhaps even someday Speaker. He has raised millions of dollars for GOP congressional candidates, given scores of speeches all over the place.

But scarcely anyone outside of Congress or his Michigan congressional district had ever heard Guy Vander Jagt until a few weeks ago. And in a year when the GOP is nominating an ex-movie actor for president, and at a time when most young politicians look as if they stepped out of a toothpaste ad, Vander Jagt seems out of place as a party spokesman.

He is paunchy at the belt, sweaty at the brow. There is the unkempt air of the ex-divinity student or backroom pol about him. Vander Jagt is both.

But since Vander Jagt was named keynote speaker, he has become something of a national figure, one of eight persons Ronald Reagan is said to be considering as a vice president running mate.

That's very heady stuff. And the importance isn't lost on Vander Jagt, a man of no little ambition.

"One way or another, it's a ticket to fame or oblivion," he said in an interview. "Many stars have been rising as they went in to give the keynote address, but after they gave it that was the end of their star. They went down in oblivion. Others came from obscurity and so electrified everyone that they went on to fame."

Names rise from the dust of the past for Vander Jagt.

"Douglas MacArthur was at the height of his oratorial power when he was selected in 1952," he says. "He'd given his 'old soldiers never die' speech before a joint session of Congress, and Taft forces had given him the keynote spot in hopes he could stop Eisenhower and lead the charge for Taft or become the nominee himself. But the old soldier bombed. That was sort of the beginning of the end for him. He didn't go up from there. He went down."

Sen. John Glenn, the 1978 Democratic keynoter, suffered a similar fate. He went to the podium one of the favorites to become Jimmy Carter's running mate. But says, Vander Jagt, "by the time he finished he couldn't have been selected to the platform committee."

"On the other side is William Jennings Bryan. He was invited to give the keynote at age 36. Nobody really knew very much about him. He wasn't one of the stars of the hour. But he so electrified the Democratic convention with his 'cross of gold' speech that he became the party nominee."

No Republican keynoter has ever fared quite as well. Most, in fact, quickly faded, and their names are all but forgotten. Who, for instance, remembers Arthur B. Langlie, the 1956 keynoter, Dwight Green from 1948, Simeon D. Fess from 1928, or Julius C. Burrows, the 1908 keynoter and the only other GOP keynoter in this centry from Michigan.

But several Republicans have made impressive marks. Warren Harding, than a senator from Ohio, was keynoter in 1916. Four years later, he won the presidency. Earl Warren, the 1944 keynoter, was the party's vice presidential nominee four years later, and went on to become one of the most influential Supreme Court chief justices in history. And Vander Jagt, ever the practical politician, claims former Rep. Walter Judd of Minnesota "is still living off the keynote he gave in 1960. I think he still gets a $1,000 honorarium every time he talks on the basis of that speech."

Vander Jagt has sifted through the speeches of predecessor keynoters, hoping to find whatever magic separates history's winners from losers. He has found little.

"The chemistry of the hall may be more important than the speech. If it's the right hour, if the delegates are in the right mood and the feeling is electric, I suspect you could give a mundane speech and they'd cheer every line. I also suspect you can give a pretty good speech and if the chemistry isn't right is just isn't going to go."

Television has complicated life for keynoters. They now speak as much, or more so, to the audience at home as to the one in the convention hall. "In some sense you're shooting a single rifle in two directions at once. You have to be hot for the audience in the convention hall and cool for the audience at home."

Vander Jagt isn't sure exactly what he's going to say Tuesday.

His speeches aren't the kind to put into stone. They read badly. They are high on Pollyanna, low on ideas. His office gives a visiting newsman printed copies of five: each contains the same quotation from Alexis de Tocqueville: "America is great because America is good and if America ever ceases to be good, America will cease to be great." He normally speaks without notes or text, and insists he isn't going to change his ways.

He has written every member of Congress asking advice and has been scribbling down lines for weeks. One favorite: "Tonight I'm the luckiest guy in America. I think of poor Mo Udall, who has to be the keynoter for Jimmy Carter and make him look good. That's not hard. That's impossible. My job is easy because I'm speaking about the next president of the United States, Ronald Reagan.

"Carter is such a beautiful target. There is one applause line after another with him. He's a keynoter's dream; he's too good to be true, he's so bad."

But Vander Jagt says he'll only mention him once or twice. Then he wants to get on to what he regards as his most important message. "I want to give American people hope and optimism. I want them to believe in themselves and their future," he says.

And perhaps remember an obscure Michigan congressman, too.