(CNN) - Democratic presidential candidate Barack Obama will start advertising for the first time in rival John McCain's home state just days before the November 4 election, Obama campaign manager David Plouffe told reporters Friday.
Plouffe said the campaign will broadcast its positive spot, "Something," in Arizona.
"We're running a positive ad there. It's Sen. McCain's home state. We're cognizant of that," Plouffe said.
All the same, the campaign considers Arizona worth fighting for.
"If someone else had been the Republican nominee, it would have been a core battleground like its neighbor Western states," Plouffe said, adding "Our internal data suggests this could be a very, very close race."
The latest CNN national Poll of Polls, released Friday morning, finds McCain leading by 4 percentage points in Arizona, which he has represented in Congress for 25 years. The poll of polls found the Republican leading Obama 49 percent to 45 percent, with 6 percent of the state's voters undecided.
Thursday's poll of polls showed Obama leading McCain by 5 percentage points, 49 percent to 44 percent, with 7 percent undecided.
A McCain spokesman dismissed Obama's advertising as a "waste of his resources."
"Voters in Arizona won't accept job-killing tax increases, won't accept a trillion dollars in new federal spending and won't accept Barack Obama," Tucker Bounds said.
But Plouffe said Arizona was in play, partly because the Obama campaign was "doing very well" with Hispanic voters and suburban voters.
He said the campaign was going back on the airwaves in Georgia and North Dakota with its negative advertisement, "Rearview Mirror," which ties McCain to President Bush.
CNN's new Georgia poll of polls shows McCain still leading Obama by 6 points, 50 to 44 percent, amid reports of overwhelming early voter turnout. There is no reliable recent North Dakota polling.
On Thursday, MoveOn.org announced it was targeting the Arizona senator with ad buys in each of the state's major media markets. The Obama camp issued a call for volunteers there, citing tightening polls in the state.
Earlier this week, the McCain campaign and the Republican National Committee paid for negative robo-calls in Arizona, telling voters Obama's election "invites a major international crisis he will be unprepared to handle alone."
CNN's electoral map suggests Obama leads McCain 291 to 163 in the Electoral College, with 84 votes there up for grabs. A candidate needs 270 electoral votes to win the presidency.