The growing voter focus on Iraq and the continued weakness of President Bush in Philadelphia suburbs such as this one are tilting the key battleground of Pennsylvania toward Democratic challenger John F. Kerry.

Bush has made 39 trips to Pennsylvania as president in an effort to swing its 21 electoral votes, which Al Gore won by five percentage points in 2000, into the Republican column -- a feat that his strategists say would almost guarantee a second term. But he has run up against a seemingly immovable barrier in voters such as Marshall Liss.

The bearded martial arts instructor has decided that the reasons the administration has given for going to war with Iraq are "ridiculous," and because of that, he regards Bush as "a complete failure." He is no enthusiast for Kerry, saying that "I thought he was clueless until I saw the [first] debate," but he has decided to "give Kerry a chance to straighten out this mess."

It is voters like Liss who are responsible for the small lead Kerry enjoyed in three independent Pennsylvania polls released this week. The most highly regarded of the trio, Franklin and Marshall College's Keystone Poll, put the Massachusetts senator ahead 49 percent to 43 percent, reversing a statistically insignificant lead Bush had a month earlier.

G. Terry Madonna, the poll's director, said Kerry's gain is directly attributable to the near-doubling -- from 12 percent to 23 percent -- during the previous month of the percentage of likely Pennsylvania voters naming Iraq as the most important issue. It is slightly ahead of the economy and tied with terrorism/homeland security in importance. Six out of 10 of those who are voting on Iraq or the economy support Kerry, more than offsetting Bush's support from four out of five voters focused on the broader national security issues.

That poll, like the others, found Kerry matching Gore's strength in the Philadelphia suburbs. In four historically Republican bedroom counties, enough Republicans and independents sympathetic to Democratic positions on abortion and the environment swung to Gore in 2000 to give him a 54,000-vote edge. Added to the 350,000-vote Democratic margin in Philadelphia and a 94,000-vote edge in Allegheny County (Pittsburgh), that advantage gave Gore a statewide 204,000-vote victory.

The Bush campaign has centered its effort on building his margin in central and western Pennsylvania, where dislike for Democrats' position on guns and abortion add to the support Bush enjoys as commander in chief.

Rep. John E. Peterson (R), whose central Pennsylvania district gave Bush almost 60 percent of its votes in 2000, said: "We have the best organization in this presidential campaign I've ever seen. We have a very tough economy, but our people like Bush."

As in other battleground states, the outer-ring suburbs and formerly rural areas in Pennsylvania that are attracting new residents are also important to GOP hopes. Lancaster County, for example, which gave Bush 115,000 votes last time, is targeted for an increase of at least 10,000 votes this year. But Madonna said that without a better showing in the Philadelphia suburbs, "it is hard for Bush to find another place to make up the votes."

Sen. Rick Santorum (R-Pa.) said the surveys he has seen in suburban Bucks County find Bush gaining support among security-minded women. Though she lives in another suburban enclave, Nan Dominick, a restaurant owner, fits the description. A regular viewer of Fox News, she said: "Bush and Cheney have been strong and consistent on fighting terrorism. Kerry is just wishy-washy."

But conversations with other voters -- and with legislators from Pennsylvania's many swing districts -- turned up a number of cross-pressures.

Gov. Edward G. Rendell (D) said that Kerry is helped by the fact that in western Pennsylvania, where Bush has strong social-issue support, "the economy is in the hopper," while in the Philadelphia suburbs, where jobs are plentiful, Bush's conservative positions on social issues weaken him, especially among women.

Rep. Phil English (R), who represents a district surrounding Erie in northwestern Pennsylvania where Bush won 51 percent of the vote last time, said the weakness of the economy makes his district "one of the toughest nuts for Bush to crack."

"My constituents -- including a lot of Republicans -- are angry about the war and about jobs, but many of them are also very hostile to Kerry," English said.

Two other Republicans, whose Pittsburgh area districts gave Bush 52 percent of the vote, see security concerns vying with worries about the economy. Reps. Melissa Hart and Tim Murphy both mentioned the anxiety about the future of bankrupt US Airways, which has thousands of jobs in the area, as a damper on optimism.

But Hart said: "On the war on terror, people know there are still people out there intending us harm, and they feel comfortable with the president safeguarding their families."

Murphy, from a neighboring district, said he finds "strong feelings on both sides of the Iraq issue, but the worry is we may be stuck there."

"People say, 'Let's work on getting out of there soon,' " Murphy added.

Here in the Philadelphia area, the battle is intense. Rep. Robert A. Brady, the city's Democratic chairman, and Rep. Chaka Fattah (D), a leading African American politician, said a successful registration campaign last year for the mayoral race set the stage for a similar effort this year that could boost Kerry's margin above Gore's. "There are two drivers for the Kerry vote," Fattah said. "There's a strong anti-Bush sentiment in the Democratic base, and health care is a critical issue."

Rep. Curt Weldon (R), whose suburban district went narrowly for Gore, said the Bush campaign has mounted "the most effective, targeted voter-identification system I've ever seen."

"They've made thousands of phone calls using marketing information on things like magazine subscriptions to develop extensive lists of people who, based on other parameters, fit the profile of the voters we need," Weldon said.

But after a wobble in early September, Kerry strategists and Rendell now see the Democratic nominee with at least a modest lead. Santorum said that he thinks "it's probably a two-point race" and that, with a healthy turnout in the Lehigh Valley and southwestern Pennsylvania, Bush might eke out a win.

For some politicians, the conflict their constituents feel is echoed at home. Retiring Rep. James C. Greenwood (R), whose suburban district went 51 percent for Gore, said his polling has found that "national security and medical malpractice reform -- we have a disaster with doctors leaving -- are strong suits for Bush."

"Even those who are pro-choice may be swayed by security concerns," he said. "My wife is a perfect example. She is a pro-choice social worker, but she says to her friends, 'My number one issue is security from terrorism, and I don't trust John Kerry on that.' "

Political researcher Brian Faler in Washington contributed to this report.