Sarah Palin on the Road in Pennsylvania

Sarah Palin has arrived in Philadelphia on day three of a mystery bus tour that is swamping US media coverage of the Republican race for the White House, leaving her rivals struggling to win attention.

Palin, who began her road trip in Washington, is refusing to provide an itinerary for the media, in what is being interpreted as payback for the hostility she faced in the 2008 election.

"It's not really an intention to play cat and mouse," she said. But the tactic has worked spectacularly to her advantage, with reporters gleefully turning her tour into a chase and guessing game about her next stop.

Reporters are enjoying the novelty so much that there is even a Twitter hashtag, #wheressarah, logging sightings and speculating on her next venue.

When reporters do catch her, the inevitable question is whether she intends to join other Republicans in seeking the nomination to take on Barack Obama in 2012. She insists she has not made up her mind. "I don't know, I honestly don't know," she says.

The 2008 Republican vice-presidential candidate may be engaged in an elaborate tease but, after a few months in which she largely dropped out of public view, the bus tour has renewed speculation that she is contemplating joining the contest.

She even admitted to reporters she had been thinking about what kind of campaign she might run, saying it would be non-traditional and unconventional – a bit like her bus trip.

She spent Tuesday at a hotel near the site of the battle of Gettysburg, in Maryland. Journalists gathered in the morning outside her bus but she had slipped out earlier to view the battlefield in peace.

The media then followed her bus to Philadelphia, where she visited the sites associated with the 1776 declaration of independence.

Her trip, accompanied by husband Todd and the rest of the family, has included the capital, George Washington's home at Mount Vernon and Fort McHenry in Baltimore, where the British laid siege in 1814.

She will almost certainly go to Boston, scene of the Tea Party. But there is speculation, too, that she will go to New Hampshire, where the second round of the Republican nomination contest will be held, a sign that political ambition rather than a historical lesson is at the forefront of her mind.

She is also planning to visit Iowa, where the first round will be held and where she is to attend the premiere of a documentary about her time as Alaska's governor.

Replying to reporters' questions about whether she will stand, she said: "It's still a matter of looking at the field and considering much. There truly is a lot to consider before you throw yourself out there in the name of service to the public because it is so all-consuming."

She has given only one interview, to Fox's Greta Van Susteren, the only reporter allowed on the bus.

Asked why she was not providing reporters with an itinerary, Palin, who has an intense dislike of much of the media, said: "They want, kind of, the conventional idea of, 'we want a schedule, we want to follow you, we want you to bring us along with you'. I want them to have to do a little bit of work on a tour like this, and that would include not necessarily telling them beforehand where every stop is going to be. The media can figure out where we're going if they do their investigative work."

The game partly explains the renewed media interest in Palin. But the attention also reflects the lack of excitement about the present Republican field.

Mitt Romney, the former governor of Massachusetts and Republican frontrunner, is due to announce his candidacy formally in New Hampshire on Thursday.

A Gallup poll of Republicans and Republican-leaning independents published on Tuesday put Romney on 17%, with Palin in second place on 15%, followed by Ron Paul on 10%, Newt Gingrich on 9%, Herman Cain on 8%, Tim Pawlenty on 6%, Michele Bachmann on 5%, and Jon Huntsman, Rick Santorum and Gary Johnson all on 2%.

These candidates have had a hard time getting on air and when they do they are almost inevitably asked about Palin.

Bachmann, who is to declare within the month, was invited on to ABC and asked how she differed from Palin. Bachmann deflected the question, saying they were friends.

Pawlenty was interviewed at the weekend and showed signs of irritation when asked about Palin.

Palin described the field as quite strong but predicted "there will be more strong candidates jumping in" and wondered about the Texas governor, Rick Perry, and others coming in. She added: "The field isn't set yet, not by a long shot." GUARDIAN