WILMINGTON - It's been a case of dueling letters.

Proponents and opponents of natural gas drilling - six in all - have recently written appeals to the Delaware River Basin Commission, increasing pressure on the agency that three years ago instituted a moratorium on natural gas development in the basin.

Until rules are adopted, there can be no drilling.

At its Wednesday meeting here, commission chair Michele Siekerka, New Jersey's assistant commissioner of water resources, responded: "We continue to confer in good faith and with forward momentum."

Drilling proponents, including Gov. Corbett, wrote letters accusing the commission of inaction amounting to a de facto ban. The Northern Wayne Property Owners Alliance in Northeastern Pennsylvania threatened litigation if the commission did not move toward adopting regulations - or stepping aside - this week.

The Wayne County, Pa., commissioners wrote that the delay was causing "irreparable economic harm." Sen. Pat Toomey (R., Pa.) called the delay "unacceptable and tremendously unfair" to his Northeastern Pennsylvania constituents.

Opponents are urging the commission to use caution and take its time.

Democrat John Hanger wrote that Corbett, whom he hopes to succeed as governor, has so "weakened" oversight of the gas industry that it cannot be adequately regulated in places where drilling is already occurring.

The Delaware Riverkeeper Network submitted a memorandum arguing against the claim of leaseholders in Northeastern Pennsylvania that the commission's inaction constitutes a violation of their property rights and a taking of their land.

Since November 2011, when a vote on proposed regulations was canceled, DRBC staff and staffs of the commission members "have spent thousands, I do mean thousands, of hours" doing more work, said Siekerka.

She said they were "benchmarking new regulations, best management practices and performance standards adopted by states, federal agencies, and other organizations."

She said the staff also had been conducting water monitoring to establish baseline conditions and had been developing a tool for evaluating the effect of land-based development on water resources.

The commission oversees water quality and quantity in the basin, which provides drinking water for more than 15 million people. It includes land in New Jersey, eastern Pennsylvania, Delaware, and New York state. Each state has a representative, as does Washington.

After the meeting, Delaware Riverkeeper Maya van Rossum said she was "struck at the suggestion that gas drilling happening is sort of a foregone conclusion."

Noting that Northeastern Pennsylvania has productive natural gas wells and is close to major consumer markets, Marcellus Shale Coalition spokesman Patrick Creighton said the commission's inaction is "hampering local economic development."

Contact Sandy Bauers at 215-854-5147, sbauers@phillynews.com, or follow on Twitter @sbauers. Read her blog, GreenSpace, at www.philly.com/greenspace