Sen. John McCain's once-comfortable lead in Arizona has all but evaporated, according to a new poll that has the underdog Republican presidential candidate struggling in his own backyard.

With less than a week until Election Day, McCain is leading his Democratic rival, Illinois Sen. Barack Obama, by 2 points, 46 to 44, down from a 7-point lead a month ago and a double-digit lead this summer, according to a poll from Arizona State University.

Factor in the 3-percentage point margin of error, and a race that was once a nearly sure thing for McCain is now a toss-up, pollsters say.

"One would think McCain would still carry Arizona, but anybody who says they can predict the state this time, they can't. It's going to depend on who goes to the polls," said Tara Blanc, associate director of the poll, which was done by ASU's Walter Cronkite School of Journalism and Mass Communication and local PBS affiliate Channel 8 (KAET).

The poll of about 1,000 registered voters indicated about 9 percent are undecided, giving campaigns few people to convince in the next six days.

Working in McCain's favor, the state has 1.1 million registered Republicans, about 96,000 more than Democrats.

In Obama's favor, the state has about 824,000 independent voters who support Obama over McCain 60 percent to 40 percent, according to the poll.

Polls tightening

Into early fall, political experts put Arizona solidly in the GOP column. But the state's polls began to tighten in late September, shortly after the Wall Street crisis and as McCain started to stumble in other states.

Both campaigns operate offices in Arizona, but their focus has been split between Arizona and the crucial neighboring swing state of New Mexico.

Neither candidate has done much personal campaigning in Arizona, instead focusing on swing states.

The ASU poll is one of at least four within the past week that indicate the race here is tightening further.

The national Rasmussen Reports has McCain with 51 percent to Obama's 46. Northern Arizona University has McCain up 49 to 41. The Project New West poll has McCain leading by 4 points, 48 to 44 percent.

RealClearPolitics.com, which tracks the last three polling averages and excludes partisan polls, gives McCain an average 6-point lead over Obama in Arizona. The results don't include the latest ASU poll.

By contrast, Obama has an average 23-point advantage in his home state of Illinois.

Presidential candidates usually win their home states, although Democratic candidate Al Gore lost Tennessee in 2000.

In 2004, Sen. John Edwards, the vice-presidential nominee, failed to secure his home state of North Carolina for the Democratic ticket.

In 1964, Barry Goldwater, McCain's predecessor in the Senate, won Arizona - but just barely. He beat Lyndon Johnson in the state by a single percentage point.

McCain confident

McCain's campaign expressed confidence in victory and suggested that Obama's unprecedented private fundraising, which includes money from donors now under scrutiny, has let him become competitive even in Arizona.

"John McCain has never lost an election in Arizona, and this one will be no different, regardless of Obama's attempt to buy the election with millions of dollars in advertising," spokesman Jeff Sadosky said in an e-mailed statement.

ASU pollsters say McCain is doing well among the state's conservative Democrats, which could give him an edge.

In 16 other states long considered more competitive, Obama has a decided polling advantage in at least eight of them.

Obama has comfortable leads in Colorado, Iowa, Michigan, Minnesota, New Hampshire, New Mexico, Pennsylvania and Wisconsin. He also narrowly but consistently leads in Florida, Nevada, Ohio and Virginia.

McCain is ahead in West Virginia.

In recent polls, both candidates have had slim leads in Indiana, Missouri and North Carolina.

Overall, McCain appears to lead in 21 states, including Arizona. Obama appears to lead in 26 states and Washington, D.C.

Three states - North Carolina, Missouri and Indiana - seem too close to call.

If the election results match those polls, Obama will have at least 338 electoral votes to McCain's 163, with 37 unclear. It takes 270 electoral votes to win.

Obama campaign officials say they are thrilled with the Arizona trend.

"Our plan remains to work as hard as we possibly can and keep the direction headed as positively as it has been," said Kelly Paisley, Obama's Arizona director.

Reporters Ronald J. Hansen, Dan Nowicki and Mary Jo Pitzl contributed to this article.