The fists were flying this week among Democrats running for governor, with Allegheny County Executive Dan Onorato and Montgomery County Commissioner Joe Hoeffel sparring and state Sen. Anthony Hardy Williams caught in the middle.

The first punch came Tuesday from Onorato's side, when five voters in Pittsburgh challenged in Commonwealth Court Hoeffel's nominating petitions for the May 18 primary-election ballot.

Hoeffel struck back, labeling the challenge a "cowardly act" from "persons acting on behalf of Onorato."

One of the voters is an Onorato appointee to an Allegheny County board. The attorney who filed the challenge has done legal work for Onorato's campaigns.

Onorato responded yesterday with this statement: "Based on the obvious motive and opportunity for one particular candidate to remove the only other candidate who shares his base, one of my supporters filed a legitimate challenge. Since no other challenges were filed as were anticipated, we are pleased that the challenge has been withdrawn and that the candidate field hasn't changed."

That's an apparent reference to rumors that Hoeffel was planning to challenge the nominating petitions of state Sen. Anthony Hardy Williams, of Philadelphia, a late entry to the Democratic race for governor. Onorato's campaign did not respond to Daily News requests to explain his statement yesterday.

Hoeffel called the Onorato statement a "lame-ass" excuse and evidence that the western Pennsylvania candidate wants two competitors from southeastern Pennsylvania in the race to split the vote.

"That is the most cynical and lame effort to play around with the Democratic process," Hoeffel said. "That is the old politics. And it shows how scared Onorato is."

Williams said yesterday that he had heard rumors that Hoeffel might challenge his petitions but that he had no contact with any other campaign on that subject.

"We certainly didn't talk to Dan Onorato about challenging Joe Hoeffel's petitions," he added.

Hoeffel's campaign submitted 7,632 petition signatures last week.

A candidate for governor needs at least 2,000 signatures, with at least 100 gathered from each of at least 10 counties in the state.