At 11 a.m. Wednesday, right after President Bush charged in a speech that John F. Kerry would "weaken America and make the world more dangerous," the speakerphone crackled in the Kerry war room on McPherson Square.

Senior adviser Joe Lockhart told rapid-response chief Joel Johnson and media man Bill Knapp from Chicago that the candidate would make no public comment but that they should crank out a commercial in response. Within three hours, Knapp and his team had cut an ad accusing Bush of "desperately attacking" Kerry, secured approval from the campaign brass, picked the markets for airing the spot and transmitted it by satellite to television stations. At 4:33, the script and a video link were e-mailed to hundreds of reporters.

"You're fighting for the network news that night and for the postgame cable cycle that evening," said Johnson, who had landed at 3:30 that morning from the vice presidential debate in Cleveland and was operating on little sleep.

Sleep is a precious commodity in the homestretch of a campaign that has moved faster with each week until it is practically a blur, especially for those engaged in the hour-by-hour combat. Several times in recent weeks, the Kerry campaign has churned out what it calls "crash ads" in an attempt to leave no Bush charge unanswered.

"We need to show the other side we have the will and capacity to respond," senior adviser Tad Devine said. "When I was a kid, we used to call it playing chicken."

The Bush campaign, of course, has its own war room in Arlington, where it makes ads just as quickly and bombards journalists with e-mail attacks on Kerry. The impact of all this instant warfare is unclear, especially since the response ads tend to fade quickly.

"A lot of these responses are geared to the press as opposed to the voters," said Brown University advertising expert Darrell M. West. "They're designed to make sure reporters understand the campaign is fighting back."

The Kerry camp's aggressiveness is a departure from the spring and summer, when the Democrat almost never parried Bush attacks on the airwaves, and it reflects the addition of Lockhart, Johnson, Michael McCurry and other Clinton White House veterans.

The intensity of the effort was underscored Sept. 22, when the Bush team unveiled a mocking ad that showed Kerry windsurfing in opposite directions, charging that his positions change "whichever way the wind blows."

The counterattack, finished in just over an hour, is known at Kerry headquarters as the "miracle spot." Set against an American flag, the ad decried U.S. casualties, kidnappings and beheadings in Iraq; called the war a "quagmire"; and declared: "George Bush's answer is to run a juvenile and tasteless attack ad."

Said Knapp: "In a world of 24-hour news cycles, we can't let these things just hang out there. They want to fuel their right-wing chatter networks."

The following Saturday, the Kerry team got word that an independent conservative group called Progress for America was using pictures of Osama bin Laden, Mohamed Atta and the World Trade Center to assail the Massachusetts senator as weak on "fanatic killers."

Knapp quickly cut an ad using an editorial from that morning's New York Times, accusing the Bush campaign of "un-American" and "despicable politics" -- even though the president had nothing to do with the unusually graphic spot. Kerry aides began calling reporters that Saturday night to alert them.

After the first presidential debate in Florida, Bush struck first with an ad seizing on one of Kerry's answers: "John Kerry said America must pass a 'global test' before we protect ourselves." Kerry's response ad was anything but subtle -- "George Bush lost the debate. Now he's lying about it" -- and it repeated Kerry's debate line about a president always having "the right for preemptive strike." Kerry aired the commercial only in Philadelphia and Detroit and on cable networks to match the Bush buy.

Kerry advisers sometimes decline to pull the trigger, depending on how widely aired a Bush ad is, what else is in the news and their strategic needs. Last week, with Iraq in the headlines, they passed on responding to a Bush spot blaming Kerry for a medical malpractice crisis. "The question is whether the response is advertising our message or whether we're falling into a trap," Devine said.

Research director Michael Gehrke maintains large computer files on foreign and domestic issues that Knapp or media strategist Michael Donilon can tap for writing the quickie ads. When a Bush spot accused Kerry of supporting higher gasoline taxes, a Gehrke staffer going through old issues of Congressional Quarterly found that Vice President Cheney had once voted to boost such taxes as a House member. The campaign also relies on Gehrke's 24-hour television monitoring and taping system for early warnings on Bush attacks.

For last Wednesday's ad accusing Bush of "desperately" attacking, Knapp drafted the script, showed it to war-room denizens Johnson and Chad Clanton for suggestions, and notified spokeswoman Debra DeShong. Knapp sent the script to one of the producers he has on call in Washington and New York, who work on Avid Technology digital editing machines. For time reasons, the visuals were kept simple. There was generic footage of people watching television (while a narrator accused Cheney of "not telling the truth" at his debate the night before), a shot of Bush and large type ("Iraq," "Bush-Cheney Failures") on the screen.

The ad was quickly approved by the brain trust: campaign manager Mary Beth Cahill, comptroller Karen Hancox, general counsel Mark Elias, Gehrke and chief speechwriter Miles Lackey.

The process moves too quickly to test the ads with focus groups. But Knapp and Donilon sometimes insert partial messages that have been tested, or order a focus group after the ad starts airing to gauge whether to stick with that message.

The ad wars often turn on dueling statistics. At 9:30 a.m. Friday, someone e-mailed Gehrke the script of a new Bush ad boasting -- after an employment report had been released an hour earlier -- that nearly 2 million jobs were created in the past year. After a conference call with Cahill, Johnson, McCurry and others, Gehrke scrutinized the report and Knapp started writing a script at 10 a.m. Five hours later, the Kerry camp announced a new spot charging that "George Bush's wrong choices have resulted in 2.7 million lost manufacturing jobs."

Why respond to an ad that wasn't an attack on Kerry? "You need to win every hour these days," Johnson said.