REFILE-Republican McCain girding for battle with Obama

(Refiling, correcting to "on" from "one" in paragraph 9)

By Steve Holland

WASHINGTON, May 9 (Reuters) - Now that Democrat Hillary Clinton is fading, Republican John McCain's U.S. presidential campaign is girding for a tough election battle against Barack Obama and McCain aides believe he has weaknesses to exploit.

In a difficult political environment for Republicans, given the weak U.S. economy, the ongoing Iraq war and Republican President George W. Bush's unpopularity, McCain will enter the general election campaign as a decided underdog.

McCain's advisers say they believe that once Democrats coalesce around their candidate, the Arizona senator's poll numbers could drop perhaps as much as 10 percentage points as the Democrat gets a bounce.

Current polls show McCain either equal to or slightly behind either Obama or Clinton in hypothetical matchups for the November presidential election.

McCain's goal is to keep the race between eight and 10 percentage points from the July 4 period to when the Republicans hold their nominating convention in early September, aides said.

If that happens, "we believe we have an opportunity to come out of the gate fast and hard and really bring a strong contrast at the time when the country is paying attention," said a top McCain adviser, speaking on condition of anonymity.

Republicans see Obama, a first-term Illinois senator, as a blank canvas -- compared with Clinton's long period in the public eye as a former first lady and now New York senator -- and thus consider Obama a difficult foe to define.