Sen. Barack Obama launched his closing Pennsylvania blitz yesterday by traveling from one corner of the state to the other, starting in Erie and closing with a massive outdoor rally on the streets of Philadelphia.

On a warm and clear spring evening, in front of a crowd estimated at 35,000, the Democratic presidential candidate told supporters that they have the opportunity to send a powerful message to the rest of the country in the primary on Tuesday.

"In four days, you get the chance to help bring about the change that we need right now," Obama said. "Here in the city and the state that gave birth to our democracy, we can declare our independence from the politics that's shut us out, let us down, and told us to settle."

And he blasted Sen. Hillary Rodham Clinton, his rival for the party's nomination, even as he called her "a tenacious opponent and a committed public servant." She is the front-runner in Pennsylvania, as Obama acknowledged last night, even though he leads her nationally.

"She's taken different positions at different times on issues as fundamental as trade and even war to suit the politics of the moment," Obama said. "And in the last few months, she's launched what her campaign calls a 'kitchen sink' strategy of negative attacks, which she defends by telling us that this is what the Republicans would do."

The crowd - the estimate of 35,000 came from officials at the Independence Visitors Center - began assembling early, filling Independence Mall and spilling into the surrounding streets. They waited with relative patience, chanting "O-ba-ma" whenever the music stopped, until 8:45, when the rally finally started. They gave him a thunderous greeting and cheered often throughout a speech that was crafted with the setting in mind.

With Independence Hall and the Liberty Bell to his right and the National Constitution Center to his left, the Illinois senator draped his familiar message in the local historical trappings.

In an obvious reference to some of his recent difficulties, he said that it was time to declare independence from "the politics that feeds on fake controversy."

Said Obama: "That may make for good headlines and good television, but it doesn't make for good government - it doesn't bring down the price of your gas or your premiums; it doesn't help you pay for college or bring your loved one home from Iraq any faster."

Earlier, in Erie, Obama held a town-hall meeting for about 2,200 people in the gymnasium at the Penn State campus.

There, he took a shot at recent comments about the economy by Sen. John McCain, the presumptive Republican nominee.

On Thursday in a television interview, McCain said: ". . . you could make an argument that there's been great progress economically over that period of time [the Bush years]. But that's no comfort. That's no comfort to families now that are facing these tremendous economic challenges."

Obama jumped on the first part of those comments.

"I see that John McCain now says that we've made great progress economically over the last seven years," he said. "How can someone who's been traveling around the country think there's been great progress?"

Obama then ticked off what he described as some of the economic indicators that have worsened even as the economy has expanded - more people without health care, people losing jobs, more people in poverty, real wages declining, and prices rising.

"Only someone who's spent two decades in Washington could make a statement that's so disconnected from the hard times that people are facing all across America," Obama said.

McCain's spokesman, Tucker Bounds, replied: "Obama is guilty of deliberately distorting John McCain's comments for pure political gain" and of being "recklessly dishonest."

During the Erie forum, one of Obama's questioners told him not to worry about the validity of his controversial comments about the attitudes of small-town Pennsylvanians, which came to light a week ago.

Said the questioner: "You can go ahead and tell people that we here in Erie are bitter about what's happened the last eight years."

Later, at Lycoming College in Williamsport, he received a similar message, this time from a teacher.

"I am a Christian, my husband is a Christian, and my husband owns guns," the woman told him. "We are not bitter about your statement. However, we are bitter about how your opponent is spinning your statement."

Today, Obama embarks on a daylong, whistle-stop train ride, starting at Wynnewood and ending with a nighttime rally on the steps of the Capitol in Harrisburg. At some stations, the candidate is expected to speak from the train as it rolls by at slow speed.

Most recent polls show Clinton leading in Pennsylvania by about 5 percentage points with the primary on Tuesday.