Seizing a chance to portray himself as the populist in the governor's race, Democrat Dan Onorato has been pounding away at GOP rival Tom Corbett in recent days on whether to tax the extraction of natural gas from Pennsylvania's Marcellus Shale.

In contrast to Corbett, Onorato favors creating such a tax and using its revenue exclusively for environmental purposes.

Onorato said Thursday at City Hall that Corbett was in the pocket of the gas industry and would prefer to have taxpayers pick up the tab for environmental damage caused by drilling than to have drillers themselves pay the cost.

Corbett has said that if elected governor Nov. 2, he will oppose all new taxes. He said that funding to protect the environment could be found by transferring money from other areas of state government. He said new taxes would only cause drillers to scale back their Pennsylvania operations, costing jobs.

"Tom Corbett thinks the taxpayers should foot the bill to clean up and protect the environment. I think the drillers should pay for it," Onorato said while accepting an endorsement from Conservation Voters of Pennsylvania.

"I am running for governor of Pennsylvania to represent the taxpayers," he said. "Tom Corbett is just representing the gas drillers."

Kevin Harley, campaign spokesman for Corbett, replied by saying Onorato's whole approach to governing was to "tax, tax, tax."

The issue of a shale tax has been bubbling in Harrisburg. As part of the agreement approving the state budget in July, legislators said they would take up by October a shale-tax proposal, including what its rate would be and how its revenue would be disbursed.

Under an agreement between Gov. Rendell and Senate Republicans, the two parties have pledged to enact a gas tax by October.

Rendell said Wednesday that he had begun to think the deal would fall through. He reiterated that Thursday in Harrisburg.

"I've been here for almost eight years. I've learned not to be confident about anything," he told reporters.

But he said a deal was possible if lawmakers sent him a serious proposal.

"Of course, it's doable," he said. "The Lord created the Earth in seven days. We have how many more days? We've got 21."

Just as Corbett disagrees with some in his party by opposing any tax, Onorato emphasized that he had not committed himself to the Rendell approach on its use and size.

Onorato said that, unlike Rendell, he would not allocate any of the revenue to help balance the budget. He said the money would go into environmental causes, including greater funding for the Department of Environmental Protection.

Rendell also wants to impose a severance tax, charging drillers 5 percent on the sale of extracted gas, plus 4.7 cents for every 1,000 cubic feet of gas produced.

Onorato said that, as governor, he expected to negotiate a tax rate with legislators.

In another campaign issue, Onorato on Thursday disputed the stance of the state Attorney General's Office that it has no authority to investigate allegations of election fraud resulting from an internal struggle this spring in the Philadelphia GOP.

Onorato had said Wednesday that Corbett, as attorney general, was playing favorites in deciding which election-fraud cases to look at and which to ignore. He said again Thursday that Corbett had "plenty of authority" to look at the Philadelphia case.

But Nils Frederiksen, a spokesman for the Attorney General's Office, reiterated that Corbett would have jurisdiction only if Philadelphia District Attorney Seth Williams referred the case to his office.

Williams' spokeswoman said he was looking into the allegations and had not asked Corbett's office to get involved.

Contact staff writer Tom Infield

at 610-313-8205 or tinfield@phillynews.com.

Inquirer staff writer Angela Couloumbis contributed to this article.