George W. Bush praises his rival John McCain as a "war hero," but he doesn't leave it at that. "John is a good man," he tells Newsweek. "I do think his story is compelling. . . . He's a straight talker."

McCain returns the favor when discussing the Texas governor. "I think he's a very fine and decent person who's been a good governor," McCain says.

What happened to the rough and tumble of a presidential campaign? Where are the harsh attacks and the mudslinging? Why are these candidates being so . . . nice?

It's early, to be sure, and the temperature is likely to rise later on. But in a marked departure from the last several presidential campaigns, most of the candidates are consciously trying to stay upbeat, muting their criticism and avoiding personal assaults. With the exception of Vice President Gore, the major contenders have clearly concluded that going positive is a winning strategy.

"Candidates have discovered you can't use attack ads like a sledgehammer or you run into a backlash," said Darrell West, a Brown University political scientist. "It has become a riskier strategy because voters have wised up and are not as likely to be influenced by thermonuclear blasts from one candidate."

Political analysts say there are several reasons for this era of good feeling, however brief it may turn out to be. Candidates who are less well known to the national electorate often feel compelled to establish their own identity before unloading on their rivals. In both parties, there are no dramatic ideological differences between the candidates, draining passion from the race. And in a time of peace and prosperity, voters are less receptive to negative assaults.

Still, it's not easy for candidates to stay positive while being pummeled. In the Democratic race, Gore is wedded to attack-a-day aggression, while Bill Bradley is trying not to be drawn into the boxing ring. "People are fed up with negative politics," he told CNN.

In the last couple of weeks, however, Bradley has increasingly been jabbing at Gore, as he did Monday on campaign finance reform. But he does not frame his criticism in personal terms. Asked yesterday on "Good Morning America" whether Gore's 1996 fund-raising had been unethical, Bradley said: "No, what I am saying is that in '96 there were disgraceful actions by both Republicans and Democrats."

Behind the scenes, where campaigns routinely fax around derogatory information, the game can be a bit rougher. McCain has accused the Bush campaign of spreading stories about his temper but acknowledges that he has no proof. McCain operatives, in turn, were quick to point out instances of Bush eruptions.

"The trick is to attach negative information to your opponent without getting blamed for having gone negative," West said.

Much of the artillery in this campaign has been fired by the media. In a spate of stories and interviews, journalists have questioned Bush's intelligence and possible past drug use, McCain's temperament and acceptance of special-interest money, and Gore's wardrobe, speaking style and choice of consultants.

McCain and Bradley, touted on Newsweek's cover as avatars of "authenticity," have pledged to run positive campaigns. They are running as maverick outsiders--war hero and basketball hero, respectively--who openly disdain negative politics.

"McCain has said from the beginning he's not going to run that kind of campaign, and McCain doesn't have to," said Mike Murphy, a strategist for the Arizona senator. "At this stage of the game, candidates can get a lot further by selling their positives, particularly if they have a story to tell."

Said Anita Dunn, Bradley's communications director: "One of the things Bradley feels very strongly about is that voters are tired of campaigns in which candidates basically seek to make them seem the lesser of two evils."

Nonetheless, Gore has tried to keep the former basketball star playing defense. The vice president has criticized Bradley's support of the drug industry, his backing of ethanol subsidies, his support for Reagan-era budget cuts, his decision to quit the Senate and his health care plan, even charging that the plan would hurt minorities and the disabled.

Bradley aides were particularly surprised when the Gore camp attacked one of their advertising consultants for having headed a firm that had a tobacco company as a client years ago. The Bradley team never raised a peep about Carter Eskew, a top Gore strategist who only last year masterminded a $40 million ad blitz by the tobacco industry against a proposed national settlement of lawsuits against the industry.

"Al Gore feels it's critical that there's a real substantive discussion on competing views," said spokesman Chris Lehane. "He feels his health care plan is the right approach and Bill Bradley's plan is the wrong approach. These aren't questions about someone's personal character. These are questions about a major policy." Bradley's approach, he added, is "cloaked in the fig leaf of a high-road style."

Gore advisers believe that the vice president's two-fisted approach has helped spur his recent rise in New Hampshire polls. "The more people see that contrast, the better Al Gore does," Lehane said. Bradley has complained of Gore's "scare tactics," accusing him last week of using poor people as "political footballs" in the health care debate.

It has been an article of faith among political operatives since Michael S. Dukakis failed to defend himself in the 1988 presidential campaign: When you're hit, you hit back hard, preferably in the same news cycle. The strategy was perfected four years later by Bill Clinton's "rapid response" team, which would call and fax reporters even before the opposing candidate had finished speaking.

Bradley, however, is moving at his own pace. "I know the conventional wisdom says that if we don't respond tit for tat on every attack they choose to unload, we're in danger of becoming a candidacy defined by other people," Dunn said. "But the conventional wisdom has been wrong about this campaign."

Gore strategists are gleeful when they prod Bradley into a testy exchange that they hope will make the former senator look like a typical politician. Gore is already saddled with the label of garden-variety pol, they say, but Bradley would look hypocritical because he espouses a higher standard for himself.

On the GOP side, Bush is also selling his sunny optimism and routinely inveighs against the "politics of personal destruction." That has always been his style, his strategists say, even when he upset a popular incumbent, Ann Richards, for the Texas governorship in 1994.

"It's never been a question of discussion inside the campaign of whether we should proactively go out with some negative, old-style, slash-and-burn campaign," said Stuart Stevens, a Bush media adviser. "He's against that because he believes that has a lot to do with poisoning the atmosphere of politics. It's very different from the sort of negative camp the Clinton-Gore administration has perfected."

Despite the placid atmosphere, campaign aides spend considerable time telling reporters, in a sort of preemptive strike, that a rival is certain to go on the attack.

"The real issue is whether the Bush campaign will go negative against McCain," said Murphy, the McCain adviser. "The Bush campaign is under a lot of pressure to get out the blowtorch and go after McCain. We think Bush would really be punished for that behavior. The minute Bush goes negative is the minute he abandons any pretense of being the front-runner."

In the same vein, the Bush camp has spent months warning of a negative ad blitz by Steve Forbes that has yet to materialize. Forbes has grown more aggressive in criticizing Bush on the stump and in debates and has taped some mildly negative commercials suggesting the Texan is too vague on the issues. But he held off on airing one such commercial after his aides tested a range of ads before focus groups.

Bill Dal Col, Forbes's campaign manager, is well aware that Forbes's 1996 air assault on Robert J. Dole sparked a backlash against the publisher-turned-politician. He says that positive ads on such issues as Social Security and taxes draw an implicit contrast with Bush's lack of specifics. "You've got a front-runner with perceived or actual weaknesses," Dal Col said. "And you can demonstrate those weaknesses by staying positive, in our case sticking to the issues."

When a campaign turns ugly, the contenders generally engage in finger-pointing over who started it. Today, Forbes begins airing his first commercial assailing Bush--and bills it as a response to a spot criticizing him by the Republican Leadership Council, which includes numerous Bush backers.

"George W. Bush says he wants a positive campaign," the Forbes ad says. "Then why are Bush's liberal supporters running this negative ad attacking Steve Forbes?"

CAPTION: Texas Gov. George W. Bush, shown at a campaign stop in Rock Hill, S.C., yesterday, has often spoken against the "politics of personal destruction."