He is on the list of possible running mates with Ronald Reagan, but Rep. Jack Kemp of New York modestly dismisses all that talk. He says he'd rather be known right now as a "wildcatter for a bold and radical idea."

That idea is something Kemp calls "incentive economics," which in simpler language means a hefty tax cut for the American people. After a remarkable metamorphosis from quarterback for the Buffalo Bills into the Galileo of Republican economics, Kemp is wildcatting the idea with considerable enthusiasm -- and promoting his own political future at the same time.

Kemp is one of the few members of Congress not in a leadership position who has a political action committee (PAC) behind him, which will finance his activities and allow him to build up political credits for the future.

The PAC, called The Committee to Rebuild American Incentive, has languished somewhat while Kemp has devoted himself to campaigning for Reagan. But Kemp adviser Charles Black, a consultant to the PAC and a former aide to Reagan, said that is about to change.

"I've just closed a deal . . . to do an aggressive direct mail campaign," he said. "It could certainly become one of the top PACs on the Republican side. Some are multimillion-dollar operations. This could be a million-dollar operation."

Using Kemp's name as honorary chairman, Black said, he hopes to raise several hundred thousand dollars between now and November, to be contributed to candidates who support the controversial economic approach espoused in the Kemp-Roth bill, which Kemp has cosponsored with Sen. William V. Roth Jr. (R-Del.).

"The guys he works closely with" -- Reps. Trent Lott of Mississippi, David A. Stockman of Michigan, Newt Gingrich of Georgia and others -- would also go out and make speeches for favored candidates, Black said.

The philosophy contained in Kemp-Roth is a cornerstone of Reagan's campaign, a fact that sets the former California governor apart from all other Republican presidential aspirants this year. The tax cut side of the bill calls for a 30 percent reduction over three years.

Kemp says it would revive the stagnant U.S. economy. Opponents have branded it "snake oil," "voodoo," "Silly Putty," and generally irresponsible economics.

Writer-professor Irving Kristol, one of Kemp's neoconservative gurus, told the Wall Street journal the other day that what is at stake in this battle of conflicting theories "is the self-definition of the Republican Party and the vision of the Republican future."

Kemp, of course, is very much part of that future, viewed in some quarters as one of the "new breed" of young Republicans attempting with some success to reposition the party, to broaden its appeal -- a conservative politician willing to consort with academics and eggheads in the pursuit of ideas.

As for the vice presidential slot, Kemp has said he would accept it if it was offered but "I don't expect it to happen. . ."

Indeed, he and his supporters agree that he played his cards all wrong if it was the vice presidential position he was after. He knew when he became actively involved in Reagan's effort last fall that it would diminish his chances, they say.

Kemp has formally discouraged the efforts of an independent group called Republicans for Victory in 1980, which has been gearing up for three months to promote him as Reagan's running mate. In a May 2 letter dissociating himself from the group, Kemp expressed concern "that the committee is diverting money, talent and other resources away from our main goal -- the nomination and election of Ronald Reagan."

Jim Roberts, former executive director of the American Conservative Union, is directing the draft-Kemp movement. Although he agrees that Kemp's activity as Reagan's economic point man hurts him as a possible running mate, Roberts said Kemp still is "the strongest running mate" Reagan could pick.

In Kemp's favor are his age, 44, his northeastern political base and his proven appeal to blue collar, ethnic and other traditionally Democratic voters of the sort that "the Republicans need desperately to win," Roberts said.

Kemp also fills Reagan's requirement that his running mate be philosophically compatible. Party regulars view him as conservative but not really "hard right," said Kemp adviser and political consultant Roger Stone, who is Reagan's Northeast coordinator.

But on the minus side others believe he is too conservative to broaden the Reagan ticket. And despite the impact of his idea on the party he, like Reagan, carries a lingering stigma as a lightweight.

Reagan needs a better-known figure of national stature, said Alan Baron, political analyst and writer. Baron said: "You raise serious questions when you nominate an actor and then add a football star . . .

Kemp's shrugs at the vice presidency are not necessarily an act of strategic coyness.

If Reagan is elected, Kemp is a natural for a top job in the new administration. Having rejected a run for a Senate seat in New York this time, Kemp mused recently that the 1982 New York governor's race "looks kind of interesting."

If Reagan loses, Kemp "would be one of the few who could mount a serious campaign for the presidency from the House" in 1964, Black said.

Meanwhile, Kemp has introduced another economic gambit. Based on an idea borrowed from two British economists, he has offered a bill designed to halt urban decay by creating "enterprise zones" in the most depressed areas to lure small businesses. Within these zones, safety regulations, most business and property taxes and other "inhibitors" would be temporarily suspended.

"I'm really excited about that bill," Kemp said, adding pointedly that it has drawn support from beyond the neoconservative movement, from some urban officials such as Rep. Robert Garcia (D-N.Y.) of the Bronx.

Kemp's name was a "red flag" at first, said a Garcia aide. But after a while they stopped using Kemp's name when they asked urban specialists, economists, and others to evaluate the idea and now, he added, "we're pretty well satisfied that it's a good thing."

Kemp, for his part, was chuckling over the news he had just received in an intelligence report that Chinese leaders are suggesting a plan very much like his "enterprise zone" bill. "I'm going to send (them) a copy of my bill," he said.

Reagan sent him a note, Kemp said, saying that he "loves it," too.