Shortly before undergoing successful open-heart surgery this summer, a man who knows something about debating an incumbent president named Bush was asked how John Kerry should conduct tonight's televised encounter with George W.

Be respectful of the office while pressing fact after fact into responses to questions, Bill Clinton replied. "Facts are not attacks." But Kerry must gird for a tougher battle than Clinton faced against Bush in 1992: "This Bush won't be looking at his watch" as the debate rolls or creeps along, the ex-president said.

It turns out to be worse than that for Kerry. Even if Bush should glance away in boredom or disdain, the nation's viewers won't see that or any other telling, spontaneous gesture. The 32 pages of rules negotiated by the two campaigns limit the cameras to showing the candidate who is speaking.

Between the filigreed lines of these rules lurk two asymmetric portraits of the fears that each campaign entertains about the other and, more significantly, about itself.

The rules constrain Kerry more than Bush. Unless the challenger is prepared to "cheat" Thursday night -- to go up to and even across the lines of prescribed and proscribed behavior -- the devil in these details will tilt the first debate into an exchange of stump speeches.

That prospect delights the Bush camp.

"We've got the better campaign speech and the only candidate who is good at delivering one," says a Bush campaign insider. An internal study by the Kerry campaign echoes this view. It found that in 2000, Bush took 18 lines from his standard speech and repeated at least one of them 59 times in three debates against Al Gore. "We have to deal with the fact he stays on message," says a Kerry strategist.

The precautions the Bush camp has taken suggest that its fears in the first debate center on Kerry's prosecutorial experience and debate techniques. James Baker, Bush's chief negotiator, seeks to protect his client's flanks with rules that prevent the two candidates from asking each other direct questions or addressing each other with proposals. And they may not roam, Clinton-style, from their podiums, when the debates move into a town hall setting.

Baker and Karl Rove clearly feel that the first debate will be decisive and in Bush's favor. They gave in without visible pain to Kerry's demand that there be a closing third debate centered on domestic and economic policy.

The challenger paid heavily for that safety-net option. He may be able to correct mistakes from rounds one and two in the closer, which will feature job losses and Roe v. Wade. But the GOP is betting that the smaller number of viewers that a third debate historically attracts will have already settled on a candidate. Opening is everything for Rove.

That leaves Kerry with both a dilemma and an opportunity in the first debate. If he displays a disciplined and polite defiance of the rules -- a defiance that communicates that those rules are being used to keep important information and impressions from the viewing audience -- he could acquire in one night the image of boldness and leadership that has escaped him on the campaign trail.

Kerry has to walk a fine line in judging how the public will view "cheating" in those circumstances. Viewers will see red lights come on in a visual reprimand to the debater who goes beyond the tight time constraints contained in the Bush-Kerry memorandum of understanding.

Each candidate gets 90 seconds to answer a minimum of 16 questions and 30 seconds to comment on his foe's answer. This two-minute limit would seem to help the "on-message" Bush and penalize Kerry's much-remarked-upon prolixity. Unless, as Kerry advisers hope, this becomes their Trojan horse: "Kerry in fact needs the verbal discipline the time limit imposes."

But the larger question remains: What will Kerry use that time to say about Iraq and foreign policy? Compressing his answers will inevitably make Kerry sound more like an all-out antiwar candidate than he has been willing to be on the stump.

In any event, Kerry made that position the only coherent one left to him by calling into question last week the credibility of both Iraq's interim prime minister, Ayad Allawi, and the elections in Iraq that the United Nations is helping to organize for January.

In 90 minutes tonight, Kerry must not only overcome Bush but also slip Houdini-like from the straitjacket of rules that Kerry willingly donned for this joust. We will know a lot more about his judgment at the end of this first, defining debate.