onight, as the clock edges toward midnight, Senator John McCain and Governor George W. Bush will sharpen their wits and vie for votes in televised campaign forums that are about as far from C-Span as they can get.
McCain will be on NBC's ''The Tonight Show With Jay Leno,'' while Bush will appear via satellite on CBS's '' Late Show With David Letterman.'' They are the latest in a bipartisan parade.
As politics steadily morphs into a branch of popular culture, and as young and undecided voters become harder to reach, leading candidates are jostling more eagerly than ever for a spot on the couch next to Leno, Letterman, and the other barons of wee-hours television.
''These appearances have become mandatory,'' said Steven Redicliffe, editor of TV Guide. ''It's like a comedy primary.''
In that ''primary,'' it is the youth vote that counts. Most late-night shows target viewers who are 18 to 34. A recent survey by the Pew Research Center for the People and the Press found that nearly 1 in 10 Americans said they regularly pick up information about the presidential campaign from Leno, Letterman, and their cohorts.
But of those respondents younger than 30, the percentage was much higher - 47 percent - who said they were informed ''at least occasionally'' by the late-night shows.
In appearing on shows that use politicians like them for monologue fodder, Bush and McCain, the GOP presidential hopefuls, will join a list that has included both Democratic candidates, Vice President Al Gore and former Senator Bill Bradley, and the two candidates for a US Senate seat in New York, first lady Hillary Rodham Clinton and Mayor Rudolph Giuliani.
The candidates are simply going where the voters are. ''If you want to reach nonpolitical people - which is, let's face it, most Americans - then you go on Letterman or Leno,'' said CNN analyst William Schneider. ''Gore knew it, Hillary knew it. It's become part of the political circuit.''
However, it is the rules of the stand-up comedy circuit that apply on these shows, and candidates ignore them at their peril. While the questions tend to be softballs, there are certain hard-and-fast rules political guests must follow to avoid becoming show-biz flops, which Leno spelled out.
''Bring some stories, have some fun,'' advised the Andover-born comedian. ''It's not `Meet the Press.' We tell the candidates to `Avoid the stump-speech answer; people are looking for the other side of you. ... Show a sense of humor, show a lighter side.'''
He added: ''No one wants a candidate to come out and say `Jay, here's my position on the S&L tax credit.' '' Leno groaned at the very thought. ''Shaaaddduuuppp!'' he said to the phantom candidate. ''You're supposed to show you're a regular guy.''
Conveniently, that is exactly what the candidates have in mind. If all goes well, as it did when Hillary Clinton appeared on Letterman's show in January, the one-liners they have assiduously rehearsed will appear spontaneous on national television.
''Hillary did wonders for herself here,'' observed Rob Burnett, executive producer of Letterman's show. Her appearance also resulted in a ratings spike, but Burnett said the idea behind booking Bush and other candidates is to have them ''come face-to-face with Dave, and Dave's sensibility, and see how they respond.''
By venturing into the late-night arena that young people have always embraced as their own, a candidate's goal is to achieve a quick image makeover as hip, fun, iconoclastic, and a good sport - in sum, a figure for whom young people should vote.
''It offers you an opportunity to show you're one of the guys, you can laugh at yourself,'' said TV historian and analyst Steven D. Stark.
Spokesmen for the Bush and McCain campaigns did not return requests for comment. On the Democratic side, Gore spokesman Douglas Hattaway said the late-night shows enable candidates to ''speak to people through the programs they actually like to watch.''
''It's more about showing the personal side of the candidate than people really get through the evening news,'' said Hattaway. ''What's more important than the message is the impression: that they can take a joke, and make a joke.''
Bradley spokesman Josh Galper said his candidate doesn't let the monologue barbs dissuade him from sitting down with the hosts who delivered them.
''You roll with the punches on these things,'' said Galper. ''They're shows where you need to have a sense of humor.'' From the standpoint of the Bradley campaign, the candidate's appearances on ''The Tonight Show'' and ''Late Night With Conan O'Brien'' are ''a great way to make outreach to all sectors of the population, because the demographics are very wide and the audience is very large,'' according to Galper. Leno and Letterman average around 4 million households per night.
Savvy candidates have long known the benefits of appearing on comedy shows. Stark noted that John F. Kennedy appeared on ''The Tonight Show'' when it was hosted by Jack Paar, and that Richard M. Nixon did a memorable stint on ''Laugh-In,'' where he intoned the show's trademark line, ''Sock it to me.''
But it was Bill Clinton who capitalized most fully on the political possibilities of these shows. First, Stark said, Clinton went on ''The Tonight Show'' in 1988 to redeem himself from a disastrously long-winded speech at the Democratic National Convention. Then-host Johnny Carson pretended to time Clinton with an hourglass.
Then, in the fall of 1992, presidential candidate Clinton played the saxophone on ''The Arsenio Hall Show,'' endearing himself to younger voters and beginning a trend that has only accelerated since then.
The candidates are so eager for late-night exposure that they overlook months of scathing treatment at the hands of the hosts. Booking Bush on Letterman's show took ''one phone call,'' according to Burnett. ''Bush and McCain are in a dogfight, so they're doing everything they possibly can,'' Burnett observed.
Likewise, Bush has been skewered relentlessly on ''The Tonight Show'' - Leno cheerfully admitted that ''We've done a lot of jokes about drug use'' and about the high rates of executions approved by the ''compassionate conservative'' - but the Texas governor finally decided that if you can't beat 'em, join 'em. He'll take his chances with Leno on Monday as a ''Tonight Show'' guest.
As for Leno, all he hopes for is a few minutes of good television. As is his policy with all candidates, he sent McCain and Bush a highlight reel of ''all the jokes I've done about them.''
Unlike ''Meet the Press,'' ''The Tonight Show'' isn't looking to break any earth-shattering news. ''You can't hope the whole republic goes in the toilet because you get 20 good minutes,'' laughed Leno. ''You can't operate on that principle.''
