The proposal by his Republican opponent, Sen. John McCain, to temporarily halt the federal gas tax to ease the pain of high fuel costs is "nothing but a Washington gimmick," Obama told about 150 invited guests during a town-hall-style discussion of the economy at Radnor Middle School.

A summer gas-tax holiday would save consumers about 30 cents a day and cause lasting harm by depleting the highway trust fund used for road and bridge construction, Obama said, adding that McCain had been silent on true energy reform.

Since clinching the Democratic presidential delegate race on June 3, Obama has embarked on a tour of battleground states to highlight solutions to economic miseries of the middle class, from rising gas prices to uncertain retirements and the rapidly rising cost of college.

He made no new proposals during the stop in Radnor Township, a prosperous Main Line suburb. Rather, he emphasized earlier ideas aimed at easing what he called the Bush administration's skew toward the wealthy.

His proposals include a $1,000 tax cut for most working families; imposing the Social Security payroll tax, now levied only on the first $102,000 of yearly income, on incomes above $250,000; a "windfall profits" tax on oil companies; and an end to income taxes for elderly people making less than $50,000 a year.

Kelly Sweeney of Hatfield, a mother of three, introduced Obama, talking about how the price of gasoline and the rapidly increasing price of groceries had squeezed her family as her husband's commission-based income dropped.

"I have watched politics as usual benefit the top 2 percent. I have stood by and watched corporate America get richer and richer while the people in my neighborhood struggle more every day," Sweeney said.

Gas prices have risen more than 33 cents in Pennsylvania in the last month, to more than $4, Obama said. "It isn't an accident," he said. "It's because Washington failed to deal with the challenge of alternative energy when it had the chance. Instead we've had an energy policy that's been written by and for the big oil and gas companies."

He said that the problem went deeper than the Bush administration - to the oil price shocks in the 1970s - but that oil and gas companies had been able to use "campaign dollars and corporate lobbyists to block reform."

Obama promised to invest $150 billion over 10 years to establish a "green energy sector" that would develop solar, wind, and biodiesel energy.

"Only Barack Obama would rail against the very lobby-driven energy bill that he himself voted for," said Tucker Bounds, a spokesman for the McCain campaign. Obama said he voted for that "far from perfect" 2005 bill because it included incentives for renewable energy.

While taking audience questions, Obama praised Thursday's Supreme Court decision to allow foreigners detained at Guantanamo Bay on suspicion of terrorism to challenge their imprisonment in federal court. Enforcing habeas corpus rights, he said, is the "essence of who we are."

Even Nazi war criminals were given due-process rights at the Nuremberg trials, Obama said. "That taught the entire world about who we are but also about the basic principles of the rule of law," he said.

On a visit to New Jersey Friday, McCain said the decision would hurt the war on terrorism, calling it one of the Supreme Court's worst rulings.

Obama said McCain would be likely to appoint Supreme Court nominees who would allow states to outlaw abortion. "You're just one justice away from that," he said, alluding to the court's narrowly divided ideology.

Obama was headed to Quincy, Ill., to help fill sandbags in a flood zone, and he is scheduled to make a speech about fatherhood in Chicago today, which is Father's Day.

Friday night, Jimmy Kimmel interviewed Obama by satellite from a conference room in Center City for a program to air today after the NBA Finals, asking how his two daughters celebrate Father's Day.

"We usually have some experiment with waffles or pancakes, and there's a lot of cleanup afterwards," Obama said. "They come with stuff we wouldn't normally put on pancakes like whipped cream. . . . Then we go to church."