Charlie Reidy couldn't bear to just watch the presidential election from the sidelines of Seattle. So he typed his name on the Internet site of Sen. Barack Obama, and two weeks later, landed three time zones away in Mt. Lebanon.

"This is where the action is," said the volunteer, working the phones from numbers on his laptop data base.

Mr. Reidy is not a Red Bull-chugging, 20-something Obama backer getting his first heady taste of presidential politics.

He is a 57-year-old retired software developer who dipped into his investments to fly across the country and spend five weeks canvassing in a state where he knows no one.

The out-of-state ground troops have landed in Pennsylvania.

This weekend, more reinforcements arrived by busload and caravan, trying to get out the vote for both Mr. Obama and his Republican Sen. John McCain.

Some were skeptical when Obama announced his 50-state strategy early in his campaign, but pundits now say he has the clear edge in the ground game.

The thousands of Obama volunteers wading into this pivotal state are not only the mainstay young, but also retirees and middle-aged professionals willing to take a leave from their jobs and sleep in someone's living room.

"Obama has created a potentially huge ground game for Nov. 4," said Terry Madonna, director of the Center for Politics and Public Affairs at Franklin & Marshall College in Lancaster. "He has more than 80 field offices in the state, probably the largest number of field operations ever in the state put into place in a presidential election.

"The reaction of volunteers and activists to help them is greater than anything I have seen in a long, long time, probably since Kennedy. I have not seen similar operations for Republicans at this point."

Bill Whalen, a research fellow at the Hoover Institution at Stanford University, said Mr. Obama's campaign has attracted a big army of volunteers, but he is not sure that they have the razor-focus of the one organized by Karl Rove in 2004, when thousands of Republican volunteers knocked on doors in the final 72 hours to get out the vote for President Bush.

Volunteers who have traveled for both candidates talk about this being the campaign of a lifetime.

"Every year, we are told this is the most important election we have ever heard of," said Megan Ritter, 22, a McCain supporter who had driven from her home in eastern Maryland to knock on doors in Delaware County. "This is the time in my life it may actually be true. We have two choices and one will mean substantial change and not in a good way and not in a way that our founding fathers would recognize. The other choice will preserve basic liberties."

The diverse group of Obama supporters in the Mt. Lebanon office has the same sense of urgency. Detailed maps in hand, they spread out into a hilly suburb that's split between Obama-Biden and McCain-Palin signs.

Kevin Kwan, a 34-year-old writer and creative director, and David Sangalli, a 33-year-old paralegal, drove in from New York City to stay in the Scott home of Jim France, Mr. Sangalli's friend. They were sleeping in his 11-year-old son's bedroom.

As graduates of "Camp Obama," a two-day training session in September, Mr. Kwan and Mr. Sangalli have knocked on at least 250 doors and have helped train other volunteers.

The lists they carried targeted swing voters. Only a few times did they go up to a house with a McCain sign planted in the lawn, and sometimes, they went up to homes with both signs in the front, a mixed political marriage. "In New York, people get a little rabid. People here tend to be respectful," said Mr. Sangalli.

They don't read off a script.

"At Camp Obama, we are trained to speak from our heart and tell our story," Mr. Kwan said. "For the first time in my life, I feel energized by the political process. My little puny effort is making a difference."

That same sense of purpose and passion was felt across town at the North Hills office of the McCain-Palin campaign.

Chip Howell, a 38-year-old training consultant, had flown in from the tiny town of Morgans Point Resort, Texas, to a state that counted. Texas was a sure Republican bet. The North Hills office was buzzing with about 30 volunteers, mostly local ones, working the phones.

"I chose Pennsylvania because I believe this is where we are going to win it," Mr. Howell said. "It's going to be decided right here in Pennsylvania, maybe here in Allegheny County."

He is sleeping at the house of a friend who is going to law school. His boss at Dale Carnegie, where he is a training consultant, let him take time off.

"This is the first time in my life I have left the state for a presidential campaign," he said. "I said, 'I have to go.' The stakes are so high."

College Republicans had also been turning out in Pennsylvania for McCain. But the youth organization said the group pulled back its field troops from this state after the embarrassment of the Ashley Todd incident, the 20-year-old student accused of fabricating about a man robbing and assaulting her because he disliked her McCain bumper sticker.

But other young people were coming in to get out for votes for McCain-Palin.

"My vote doesn't mean squat in Maryland," said Ms. Ritter, the 22-year-old from Maryland.

Conversely, Mr. Reidy, the retiree from Seattle, can afford time to spend on an out-of-state race. And in Mr. Obama, he has found the first truly inspiring Democratic candidate since the 1960s. He typed his name into the volunteer Web sites of Pennsylvania and Ohio, and heard back from Pennsylvania organizers first.

Mr. Reidy had planned to spend his money on a trip to Europe this fall. But his travel plans changed when Mr. McCain named Alaska Gov. Sarah Palin his vice presidential candidate.

So instead of Rome and Prague, he traveled to the less touristy streets of Mt. Lebanon to do battle for Mr. Obama.