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With just one week to go, the two men vying for the White House fought for votes Tuesday in battleground Pennsylvania - a solidly democratic state in the past four elections where Barack Obama holds an almost 10-point lead.

Republican candidate John McCain is fighting to turn the state red from blue as he faces a daunting seven to eight-point deficit nationally behind Obama.

"I'm not afraid of the fight, I'm ready for it," McCain told supporters at a rally in Hershey, Pa., a Republican region in the southeastern corner of the state, home to the world's largest chocolate factory.

McCain appeared with his vice-presidential running mate Sarah Palin, who said it would be a "hard-fought contest" in Pennsylvania. "It's going to come down to the wire here."

Should McCain fail to win Pennsylvania's 21 electoral votes, it may be almost impossible for him to win the presidency. The reason is Obama is expected to win several of the states that helped re-elect President George Bush four years ago. McCain needs one of the Democratic states to make up for expected losses in the Republican ones.

Michael Berkman, a political science professor at Penn State University, said the McCain camp is holding onto hope in the state for a few reasons: "There's no early voting, so it's not like any votes are already locked in for Barack Obama," he said. "And Barack Obama did not run well here against Hillary Clinton, so I think that probably gives the McCain camp some hope."

The Obama camp, although confident it will win the state, still sent the candidate to the Philadelphia suburbs on Tuesday after rallying supporters Monday night in Pittsburgh.

"I just want all of you to know that if we see this kind of dedication on election day, there is no way that we're not going to bring change to America," Obama told a group of about 9,000 supporters in the rain at Widener University on Tuesday.

Obama repeated that a vote for McCain would be a vote for a third George Bush term.

"John McCain has ridden shotgun as George Bush has driven our economy toward a cliff, and now he wants to take the wheel and step on the gas," Obama said.

McCain, meanwhile, continued to try to convince voters that Obama is a risk, painting him as a traditional liberal Democrat who wants to redistribute wealth -- and who's even willing to disturb a World Series baseball game on Wednesday night with a 30-minute commercial.

"No one will delay a World Series game with an infomercial when I'm president," McCain said.

McCain said Obama's promise not to raise taxes on people making less than US$250,000 can't be trusted. He pointed out that Obama's running mate, Senator Joe Biden, told local television station WNEP that tax relief should only go to "middle-class people -- people making under $150,000 a year."

"At this rate, it won't be long before Sen. Obama is right back to his vote that Americans making just $42,000 a year should get a tax increase," McCain said.

The numbers

A national poll by the Pew Research Center found Obama with a 16-point lead among registered voters. The survey said Obama had 52 per cent and McCain 36 per cent, with independent voters supporting the Democrat by a 48-31 margin.

A Zogby poll shows a tightening of the race, with Obama leading only by 4.3 per cent - down from 12 points last week.

But Zogby communications director Fritz Wentzel said the "real" story is in the battleground state numbers.

"If you look at some of the key battleground states, Obama has a fairly dramatic advantage," Wentzel told Â鶹´«Ã½net's Mike Duffy Live on Tuesday. He added, however, that it isn't yet a "slam dunk" for Obama, since he's still within the margin of error in many of those states.

Wentzel said almost all of the states that are being contested are former Republican states -- good news for Obama, especially since he's leading in three key ones, including:

• Virginia -- a Republican state with 13 electoral college votes. The state is tilting blue because of a change in demographics resulting in new Democratic voters.
• Florida -- Obama has a significant lead for those who have voted in advance. It's tied between those who have not yet voted. "So if Obama can hold his tie," said Wentzel, "that state very well may go democratic blue."
• Ohio -- among those who've already voted, Obama has a huge lead -- 68 per cent versus 23 per cent for McCain. Among the other 83 per cent who haven't voted, McCain has a five-point lead. "But he's got to increase that lead by about another four points for him to overtake Obama overall," said Wentzel.

"So if he loses any one of those three states, it would be very troublesome for McCain to win the presidency," he added.

With reports from CTV Washington Bureau Chief Tom Clark and The Associated Press