NEW YORK - Belittling John McCain as a relic of the disco age, Democrat Barack Obama pushed his campaign Friday to a new level of counter-punching "on the issues that matter" and directed his running mate to be tougher on their Republican opponents.

The changes come as national polls find McCain and his running mate, Alaska Gov. Sarah Palin, pulling ahead of Obama and Joe Biden, prompting some jittery Democrats to implore them to fight back harder, and Obama's camp to pledge "speed and ferocity" in that effort.

"You know, I'm not going to be making up lies about John McCain," Obama told undecided voters in Dover. But he dipped into history, citing the oft-repeated phrase: "If you don't stop lying about me, I'm going to have to start telling the truth about you."

"That's what we're going to do," Obama said.

Dover resident Glenn Grasso asked Obama, "when and how are you going to start fighting back against attack ads and the smear campaigns?"

"Our ads have been pretty tough," Obama replied. "I'm going to respond with the truth."

Obama has called Palin a "phenomenon" and acknowledged she's given her ticket a boost. But his aides say McCain is vulnerable to new criticisms because he has stretched the truth in recent comments and ads, and because Palin was shaky on foreign policy in an ABC News interview.

"Today is the first day of the rest of the campaign," Obama campaign manager David Plouffe said in a statement Friday. "We will respond with speed and ferocity to John McCain's attacks and we will take the fight to him, but we will do it on the big issues that matter to the American people."

Plouffe said Biden "will be integral to that effort, both in pushing back on the lies that we'll continue to see from our opponents, and in keeping the debate focused on delivering for everyday Americans."

Vice-presidential candidates often play the role of attacker. But many Democrats feel their party's last two nominees for that job, John Edwards and Joe Lieberman, were too passive.

The newest Obama TV ad gets personal and makes a none-too-subtle dig at McCain's age. It shows McCain at a hearing in the early 1980s, wearing giant glasses and an out-of-style suit. Other images include a disco ball, clunky phone, outdated computer and Rubik's Cube. "Things have changed in the last 26 years," the announcer says, "but McCain hasn't."

"He admits he still doesn't know how to use a computer, can't send an email, still doesn't understand the economy, and favours $200 billion in new tax cuts for corporations, but almost nothing for the middle class," the commercial says. McCain has said he relies on his wife and staff to work the computer for him and that he doesn't use email.

The non-partisan Tax Policy Center says McCain's proposed corporate tax cuts would total about $231 billion over four years. It says McCain's proposals for individual tax rates "would primarily benefit those with very high incomes." It says many fewer households "at the bottom of the income distribution would get tax cuts, and those tax cuts would be small as a share of after-tax income."

The Obama ad closes with a photo of McCain standing with President George W. Bush. "After one president who was out of touch," the announcer says, "we just can't afford more of the same."

Another new Obama ad repeats criticisms of McCain for having current and former prominent lobbyists on his campaign staff. A third new ad is more positive, highlighting Obama's change message and saying he will provide better health care and tax breaks.

Republican National Committee spokesman Alex Conant said Obama is "trying to destroy" McCain and Palin with personal attacks.

McCain, meanwhile, released a new ad saying Obama has been "disrespectful" in his treatment of Palin, who seems to be making inroads among female voters in several states.

Democrats said Senator Hillary Rodham Clinton, who narrowly lost the nomination to Obama, will campaign for him at two stops Sunday in Ohio.

In Dover on Friday, Obama rebutted McCain's claims that he would raise taxes on working-class families. "I pledge that under my plan, no one making less than $250,000 a year will see any type of tax increase," he said. "Not income tax, not capital gains taxes, not any kind of tax."

He also criticized McCain for recently saying the economy is making progress under Bush. "We can't afford four more years of what George Bush and John McCain consider progress," Obama said.

When some in the audience shouted that Republicans have lied about him, Obama said, "Lies, that's the word I was looking for."

"We have been hitting back hard, but we're hitting back on the issues that matter to families," he said.

The Democrats' 2004 nominee, Senator John Kerry, said in a new fundraising letter for Senate candidates: "This is what I learned in 2004. When Republicans go on the attack with their lies and innuendo, Democrats need to hit them back twice as hard."

Some independent analysts say McCain's flurry of claims and criticisms this week seemed to catch Obama off guard.

Kathleen Hall Jamieson, a University of Pennsylvania authority on political communications, said Obama erred by focusing on one dubious McCain assertion -- that Obama had indirectly insulted Palin by using a phrase about putting lipstick on a pig -- while the Republicans hit him with a more damaging claim misrepresenting his position on sex education for kindergartners.

"When someone says you want to teach kids about sex, you should counterattack immediately, and they didn't," Jamieson said. "They said they were outraged, but the outrage was lost among the outrage about lipstick. The Obama campaign didn't pivot fast enough when that ad went up."

Friday's message from the Obama camp seemed to be: Don't worry, we're firing on all cylinders from now on.