"The choice in this election is stark and simple," McCain, the presumptive Republican nominee, told a town-hall meeting in Denver. "Sen. Obama will raise your taxes. I won't. I will cut them where I can."

Obama, the presumptive Democratic nominee, countered by challenging McCain and promising he would not raise taxes on anyone earning less than $250,000 a year.

"If Sen. McCain wants a debate about taxes in this campaign," Obama told supporters in Charlotte, N.C., "that's a debate I'm happy to have." Obama spoke via a telephone hookup after his Charlotte-bound plane was grounded in St. Louis because of mechanical trouble.

Neither candidate's address contained new proposals. McCain's chief purpose was not only to shift his campaign's focus squarely to the economy, but also to reignite his White House bid after weeks of organizational trouble and muddled messages.

Carly Fiorina, a senior McCain adviser, described the new phase as "a little bit like a start-up company becoming a multimillion-dollar corporation."

McCain tried to put some distance between himself and his party, criticizing Congress and the Bush administration for having "failed to meet their responsibilities to manage the government."

McCain has been a senator since 1987, however, and Obama charged that "he's launching a new economic tour today with politics that are very much the same as those we have seen from the Bush administration."

Many of McCain's ideas are similar or identical to President Bush's, notably his support for continuing key elements of the 2001 and 2003 tax cuts, which are scheduled to expire during the next administration.

Asked to list three ways Bush and McCain differed on the economy, Fiorina struggled and listed only one: better job training for displaced workers.

Obama says he would restore higher, Clinton-era income-tax rates on people earning more than $250,000. The top rates before 2001 were 39.5 percent and 36 percent; now, they are 35 percent and 33 percent.

One to 2 percent of all wage-earners make more than $250,000. Obama said he would not raise taxes on anyone else.

"If you're a family making less than $250,000, my plan will not raise your taxes: not your income taxes, not your payroll taxes, not your capital-gains taxes, not any of your taxes," he said yesterday.

McCain, who did not discuss how his tax plan could avoid worsening the federal budget deficit, countered that repealing the Bush cuts as Obama has proposed would have a ripple effect and be more widely felt. One reason is that the tax on dividends and capital gains, now 15 percent, is slated to rise in 2011.

Because of that, McCain insisted, "If you have an investment in your child's education or own a mutual fund or a stock in a retirement plan, he is going to raise your taxes."

McCain, who also wants to lower the corporate tax rate, would retain current dividend and capital-gains tax rates, saying: "When you raise taxes in a bad economy, you eliminate jobs. I'm not going to let that happen."

Obama suggested that keeping such rates low would be a boon only to big business and wealthy taxpayers.