After a week spent trading barbs with the Bush administration over his explanation of his votes on the conflict in Iraq and his approach to the war on terrorism, John F. Kerry took a new tack Thursday.

He changed the subject.

With a morning conference call led by policy aides and a speech in the Los Angeles area, Kerry launched what advisers say will be a two-week-long focus on the economy, which aides said has emerged in polling as the top issue in the November election.

Kerry proposed a revamping of the Bush administration's tax policy that he said would ease the tax burden on middle-class Americans.

"Middle-class families can't afford four more years of a tax plan that drives up unemployment, drives up the deficit, and drives up their tax burden and the costs of health care, child care and college tuition," he told a crowd of about 500, in a theater on the campus of California State University at Dominguez Hills.

The Democrat accused President Bush of failing to advance a viable economic plan during his tenure. "There's a very simple reason that we've gone four years without a real plan to fix [the economy]; no one in the White House thought anything was broken," he said. "And they still don't. They're just fine with the same old failed policies of the past."

Kerry said he was looking instead to some of the successful policies of the past, namely those of former president Bill Clinton. He said Clinton's advisers were helping devise his economic plan and that he would be "a champion for the middle class" by cutting their taxes and lowering the deficit. "They will go back to paying the same taxes they paid when Bill Clinton was president," Kerry said. "That was a time when every American got richer."

Clinton administration deputy Treasury secretary Roger Altman said in the call to reporters that Kerry planned $419 billion in new tax cuts aimed at the middle class, for businesses that create jobs in the United States, for college tuition, for child care and for expanding broadband Internet access, among others. He criticized a plan floated by Bush this week for a nationwide sales tax. "If you spent a year, you couldn't come up with a more regressive proposal than that," Altman said.

The cuts would be paid for mostly by repealing tax cuts given by Bush to those earning more than $200,000 a year and closing various tax loopholes, according to a chart provided by the Kerry campaign.

A Bush spokesman said that Kerry's numbers do not add up. "He has spent his tax hike more times than anyone can keep track of," Steve Schmidt said. "And his own director of economic policy has said that the Kerry tax plan isn't paid for."

Kerry advisers said that emphasis on economic issues was in part a response to recent polls that voters considered them key to the election. It is also an area in which they believe the president is vulnerable. Recent economic data, including job creation numbers released earlier this month, have challenged administration claims that the economy is turning the corner.

And a Pew Research Center poll released Thursday showed that 52 percent of the 1,512 adults polled believed Kerry could best improve the economy, compared with 37 percent for Bush.

While Kerry avoided in his remarks here any mention of Iraq and the increasingly personal attacks by Vice President Cheney on his credentials to fight the war on terrorism, he did respond to a reporter's question about them. "It's sad that they can only be negative. {grv}They have nothing to say about the future vision of America," Kerry said backstage as he waited to give his speech.

Kerry aides said the administration attacks were an effort to distract the public from economic issues.

In Carson, Kerry joked about the state's GOP governor, Arnold Schwarzenegger, saying that he was similar to the action star-turned-politician, who replaced Democrat Gray Davis after a recall election last year, because "Arnold has massive biceps, and I have massive hair."

Kerry's speech met with raucous applause and chants from an audience that included students and faculty, and a host of politicians, including Davis, seated in the front row of a theater.

Kerry's plan to reward companies that keep jobs in the United States impressed Greg Mitre, 46, a longshoreman from the San Pedro section of Los Angeles. "In my business, we benefit from jobs going oversees, 'cause it usually means more trade, but I'm still against it," Mitre said. "We've lost too many jobs in the L.A. area already."

At an evening rally on a fair ground in Center Point, Ore., Kerry took a swipe at Bush's lack of service in the Vietnam War. "I defended our country as a young man, when others chose not to," Kerry said, in an oblique reference to the president. "And I will defend it as president of the United States."

Sen. John F. Kerry said he would ease the tax burden on the middle class.