There were two politicians at or near the top of their game on the stage Friday night, and the effect was striking.

In the second campaign debate, President Bush sharpened his performance considerably over his first encounter with Democrat John F. Kerry, the result being rough parity between the candidates on stylistic grounds. That put their differences on substance -- dramatically different governing priorities, and starkly different responses to whether the country is on the right course at home and abroad -- on even more vivid display.

An evening of tough and well-stated questions from undecided Missouri voters in the "town hall" format succeeded in laying bare more clearly than at any time this campaign season the essential choice facing voters on Nov. 2. In impassioned and plain-spoken language, Bush defended his course on Iraq, tax cuts and the right way to improve the economy, and said it deserved validation with a second term. In equally blunt terms, Kerry asked voters to perform a "gut check" and ask themselves if Bush's policies or his words -- which the Democrat labeled "Orwellian" -- held any credibility.

As he did in the first debate, Kerry turned every question into an opportunity for a scathing critique of Bush's policies. In several cases, he used Bush's own words against him, including promises about the right circumstances for sending troops abroad that Bush had uttered in the same auditorium at a debate four years ago. More often this year, it has been Bush who has sought to torture Kerry by summoning up old quotations.

But Bush responded to Kerry's charges this time with answers that were both more vigorous and more conversational than at the first debate, Sept. 30 in Miami.

Answering one question, he said he has no regrets about invading Iraq, rejecting a treaty on global warming, dismissing the Palestinian Authority's Yasser Arafat as a credible leader and negotiating partner -- decisions that raised objections in other countries.

"People love America," Bush said. "Sometimes they don't like the decisions made by America, but I don't think you want a president who tries to become popular and does the wrong thing."

With two debates down and one to go -- the last, on domestic policy, Wednesday in Arizona -- it did not seem likely that this debate will dramatically affect the dynamic of the campaign, in the way that Bush's weak performance in Miami clearly presented an opening for Kerry and tightened the polls to what is now essentially a tie.

The encounter at Washington University here also shattered some conventional wisdom about town hall debates. This had held that they were supposed to be more genteel affairs, because politicians supposedly do not wish to be too aggressive in a more intimate setting before real voters. Not so this evening: At every single question, Bush and Kerry challenged each other sharply, sometimes in caustic language.

Kerry said Bush's failure to plan adequately in Iraq meant "our kids are being killed" because they were inadequately armed and more nations are not contributing troops. He turned nearly every answer into an argument that the country needs to change course.

In his answers, Bush returned to familiar lines of attack: that Kerry is too irresolute a politician, and too liberal on issues involving taxes and support for the military, to be trusted to lead in an age of terrorism.

Both men moved effectively to address what had been potential deficiencies. In an answer about stem cell research and whether it involved taking a life, Kerry talked more personally about his Roman Catholic faith, mentioning his youth as an altar boy, than he typically does in public. Defending his plans to raise taxes -- but only on those with high incomes -- he joked that the only people in the room affected would be Bush, moderator Charles Gibson of ABC News and himself. Whether that line will come off as self-aware wit, or another way of saying that the audience looked like a bunch of schlumps to him, remains to be seen.

In the very first question, Kerry was pressed to answer Bush's most frequent criticism of him, when Cheryl Otis asked him to address the observation of her family and co-workers who believe the Democrat is "too wishy-washy." Kerry dismissed the criticism as a fiction of Bush's campaign, as he has done before, but this time with more specificity. Citing the USA Patriot Act, for instance, he said it is reasonable to have supported the legislation but have objections about how it is being applied, and noted that even prominent Republicans have similar concerns.

Plainly eager to rebut Bush's charge of liberalism, potentially devastating with independent voters, Kerry also accused him of "just trying to scare everybody here with throwing labels around. I mean, 'compassionate conservative,' what does that mean? Cutting 500,000 kids from after-school programs, cutting 365,000 kids from health care, running up the biggest deficits in American history."

Bush, too, made important alterations to his performance. He pushed back just as aggressively as he did in the first debate against Kerry's criticism, but he did so with less of the peevish edge and dismissive facial expressions that even his own aides agreed marred that performance.

After Kerry spoke on Iran, Bush joked, "That answer almost made me want to scowl."

The evening's format was one that posed challenges for which both men had reasons to be wary. In 1992, the town hall debate in Richmond effectively sealed the fate for President George H.W. Bush's troubled reelection candidacy, during an evening when the current president's father interacted awkwardly with questioners and kept glancing at his watch in a way that conveyed unmistakably that he could hardly wait to be somewhere else.

At the same occasion, challenger Bill Clinton displayed the raspy-voiced empathy that was his signature and helped set an new expectation for presidential politics: Candidates should be judged on the ease and persuasiveness with which they can converse in the language of the Middle American kitchen table.

The reality of this year's candidates -- two sons of privileged families, two Yale graduates, two millionaires -- is that they are far removed from that table. At the outset of his presidential campaign, Kerry acknowledged that he can strike people as distant when he joked that he was undergoing surgery to have his "aloof gland" removed. Bush, a natural back-slapper and towel-snapper, is generally credited with winning the "regular guy" derby. In political terms, however, he usually runs behind Kerry in the now-standard poll question of which person "understands the concerns of people like you."

But the St. Louis debate may have reshuffled expectations also for "town hall" debates. The questions voters asked were not parochial, and fit into none of the old conceptions about issues that supposedly concern "soccer moms" or "angry white men." They were the same questions, indeed, that any panel of think-tank experts might have composed. These question also proved that a year of tough campaigning has left the candidates sharper with their answers than ever.

At the conclusion of the second of their three nationally televised debates, the president offers a word to his Democratic challenger.