The furor over President Bush's National Guard records and a suspected forgery ensnaring CBS News is one of those unpredictable episodes that buffet presidential campaigns with near-perfect predictability.

This controversy, according to media analysts and veteran political operatives, has some distinctive details but is almost routine in its main elements: allegations of political dirty tricks, a whodunit mystery, a flood of news coverage, and its timing in the last weeks of summer and the beginning of fall.

September -- after the conventions but before the presidential debates -- has proved repeatedly to be a fertile moment for sensational scandals that can temporarily dominate the campaign, even as they rarely are consequential to the outcome and recede rapidly in memory once the election is over.

During this same period in the 1992 campaign, there was a fracas over Democrat Bill Clinton's trips to Moscow as a young man two decades earlier, what he had done at war protests in England, and whether the George H.W. Bush administration had improperly rummaged through Clinton's passport records looking for political dirt.

In September 2000, there was a hubbub that dominated campaign debate for several days over "RATS." Aides to Democrat Al Gore, after conducting frame-by-frame analysis of George W. Bush's television spots, noted that the R-word briefly flashed across the screen in what they said was intended as a subliminal smear. Bush aides denied it and suggested that Gore's side had come unhinged.

Campaign observers independent of Bush and Democratic nominee John F. Kerry have competing views on these drenching September storms.

Some regard them as unwelcome detours, especially as the controversies often center on long-ago events in candidates' lives or the tactics of political pot-stirrers -- the National Guard-CBS story involves both -- rather than contemporary issues confronting the electorate. For a few days this month, the controversy had political journalists and campaign operatives alike consumed with such questions as whether IBM Selectric typewriters of the early 1970s could type superscript of the sort found on the purported Guard memos.

Don Baer, a former magazine journalist and communications director in Clinton's White House, noted the "paradoxical situation" of an election during a time of war when "the stakes are manifestly so high" being diverted by "essentially trivial things."

Others take a more relaxed attitude. Voters, according to this view, can learn useful information about how would-be presidents react to unplanned campaign controversies. Republican media consultant Roger Stone, in e-mail comments to a reporter, said he subscribes to the adage that "if you want to see what kind of leader someone will be, watch how they conduct themselves in the fire of a campaign."

Stone, who has worked for Republicans as far back as Richard M. Nixon, said it is no surprise that there is media and voter curiosity about such questions as whether Kerry's Vietnam War service was as heroic as he and his supporters portray it, or whether Bush is hiding a scandal about his National Guard service. "Our politicians are celebrities, and we want to know their secrets as much as we want to know Brad Pitt's or J. Lo's," he said.

This comment suggests another way in which the 2004 campaign may be riper than ever for furors about the candidates' personal histories and campaign tactics. Increasingly, the contest is being waged over personal attributes -- Bush saying Kerry is too weak and indecisive to be president, Kerry saying Bush lacks credibility. An election waged over character puts a premium on stories that suggest evidence of hypocrisy.

"It's through the prism of character that we best understand candidates' positions on issues; it's the most accessible way we come to understand whether they are right or wrong on the economy or defense," said Paul Taylor, a former Washington Post reporter who is vice president of the Pew Research Center. "In a rough and rugged way, this campaign is getting the big issues before the public."

Mark Halperin, political director of ABC News, cautioned that people in the media may overestimate how much most voters care about controversies that journalists and political operatives find riveting.

"The dominant narrative of a campaign is written by people who care about politics" in the context of strategy and tactical maneuver, rather than how it affects, for instance, the cost of college tuition, he said. "The easiest stories for major newspapers or networks to do are media stories or 'controversy' stories. . . . They are the ones that feel the most immediate and buzz-creating to people in a newsroom who sit around all day reading the Internet and watching cable TV, and even if people know the audience for these [outlets] is small, they are hypnotically lured into the notion that these stories are creating the water-cooler buzz, and they do not want to miss the hot story."

A Gallup Poll released this past week showed that public confidence in the news media is waning. Forty-four percent of Americans said they had "trust and confidence" in the mass media -- 9 percent said they had a "great deal," and 35 percent a "fair amount." This was down from 54 percent who reported confidence in the same survey a year earlier. The survey was taken in the days after questions were raised about the "60 Minutes" broadcast on Bush's National Guard service but before CBS News apologized for not adequately checking its reporting.

While the episode was a black eye for one of the most storied names in journalism, media analysts and political strategists say the larger reality that this year's campaign has highlighted is the deterioration of mass media's dominance.

Twenty or even 10 years ago, presidential campaigns and major media organizations tussled over control of the agenda -- pitting the candidates' pronouncements against other issues that reporters and producers thought worthy of attention.

This year, other forces -- a proliferation of ideologically motivated Web sites and independent political organizations such as the anti-Kerry Swift Boat Veterans for Truth or the liberal Media Fund -- have entered the fray. Control of the election agenda is less a tug of war than a barroom free-for-all.

"It's everybody, and nobody" who gets a say in setting the agenda, Baer said.

Traditional news organizations, Taylor agreed, "have this gate-keeping role in a world where it's very difficult to have gates, because anybody can come crashing in."

Those who do not like this, he added, can take heart in the probability that the phase of the campaign dominated by fights over the candidates' pasts is in all likelihood at an end, with three nationally televised presidential debates looming. "The public wants to make a grown-up decision," Taylor said. "That's not to say that people are not interested in these whodunits, but in the end, voters do care about issues."

Disagreements over episodes from long ago, in this case the National Guard service of Republican George W. Bush, can pop up at inopportune times, from a candidate's point of view.For Democrat John F. Kerry, his service record in the Vietnam War was challenged. Some experts sees these late summer diversions as valid tests of the candidates under fire.