HARRISBURG — Five Republican state senators have written to their caucus leader, asking him to revive the stalled negotiations over imposing a new tax on natural gas extraction that Gov. Ed Rendell has said were killed by their party.

The five southeastern Pennsylvania lawmakers wrote to Senate President Joe Scarnati late last week, urging him to work toward enacting a tax on the state's booming Marcellus Shale gas exploration before this year's legislative session ends.

They disagreed with the Democratic governor's claim that Republicans have not bargained in good faith, but said the state cannot miss the chance to establish a reliable source of tax revenue.

"We also believe that any agreed-to legislation should include a regulatory scheme that will provide enhanced environmental and safety protections to prevent damage to our environment while ensuring that we have a sustainable natural gas industry," they wrote.

Sens. Ted Erickson of Delaware County, Stewart Greenleaf and Bob Mensch of Montgomery County, and Chuck McIlhinney and Robert Tomlinson of Bucks County sent the letter.

Rendell on Thursday declared the tax dead, saying Republicans had not budged in negotiations or demonstrated any interest in compromise with Democrats.

"Their clear unwillingness to change their previous proposal or to resolve differences with the House Democrats and with my administration makes it obvious that they have killed the severance tax in this legislative session," Rendell said.

At a news conference Tuesday in Philadelphia, where he signed an executive order to prevent any additional leasing of state forest land for drilling, Rendell called the five state senators who wrote the letter "all decent men, but they're all running for election."

"If these five had said, 'Let us vote on the governor's compromise,' you know what would have happened? The compromise would have passed," he said.

"Unless you can get your caucus to list it for a vote, then being for it is easy. It doesn't mean a single bloody thing."

Rendell also urged both gubernatorial candidates to sustain his moratorium on leasing more forest land for gas drilling, which he said is needed to protect the state's tourism and lumber industries.

Republican Tom Corbett would rescind the moratorium and Democrat Dan Onorato would keep it, spokesmen for their campaigns said. Rendell is leaving office in January.

Tomlinson said the shale tax has not been a major issue in his campaign.

"I'm not feeling any particular pressure here from my race, and I've stated publicly that I'm for a Marcellus Shale tax," he said.