PHOENIX — A new poll suggests that John McCain may need to spend a little more time campaigning in his home state if he wants to chalk up a win here.

 The survey shows Democrat Barack Obama now within 5 points of the Phoenix resident and presumptive Republican nominee in Maricopa County. Jim Haynes, president of the Behavior Research Center which conducted the poll, said that close a race in the state’s largest county, where Republicans outnumber Democrats by a margin of close to 3-2, means the state’s senior senator needs to pay attention.

 “I think its a sign that Arizona’s in play. McCain’s going t have to spend some time shoring up the home front,’’ he said.

 More than half of all registered voters are in Maricopa County.

 Haynes noted that much of the shift comes among male voters.

 In May 2007, he said, McCain had a 23 point edge over Obama amon this segment, a figure that actually rose to 26 points this past May. But by the fourth week of July, when the survey of 401 voters was conducted, McCain’s lead among men had shrunk to jus 4 points.

 Some of that, said Haynes, may have been expected. He pointed out that the polling was conducted while Obama was in the Middle East and Europe.

 “He was the subject of pretty intense media coverage,’’ Hayne said. More to the point, he said that Obama was getting a lot o publicity “with respect to his ability to deal with world leader and that kind of thing which I think most people believe is one of the areas where he’s tended to be on the weak side.’’

 McCain also lost ground among Hispanics. He was the choice of 2 percent of Latinos in May 2007; that has now dropped to just 9 percent.

 Obama’s gains among those groups, however, appears to have been offset somewhat by other voters, notably women. But that also appears to be true for McCain, as Haynes said the number of women who went from supporting one of the candidates to undecided has swollen.

 And independents are virtually evenly split between the pair.

 That left Obama the choice of 38 percent of Maricopa County residents, the same figure he was at more than a year earlier. B contrast, McCain’s support among voters in the county went from 53 percent in May to 43 percent in July.

 Calls to the McCain campaign were not immediately returned.

 At this point Ralph Nader does not appear to be much of a factor: He is the choice of only 3 percent of those asked.

 The survey has a margin of error of 5 percent.