Members of a government task force continued to walk a fine line yesterday on the issue of state-versus-federal regulation of shale gas drilling and hydraulic fracturing.

The panelists testifying yesterday at a Senate Energy and Natural Resources Committee hearing offered high praise for state regulators' current efforts to police the rapidly growing shale gas drilling industry, but they stopped short of backing either state or federal regulation for shale drilling.

"I think there's a gap in perception" about "the idea that oil and gas activities are not regulated at the state level," energy consultant and author Daniel Yergin said at yesterday's hearing. "We were all impressed by the focus of the states."

Yergin is a member of the group tasked by Energy Secretary Steven Chu to recommend ways that shale gas can be exploited while maintaining environmental safety.

"State regulators successfully regulate shale gas development and production," said another panelist, Kathleen McGinty, senior vice president of Weston Solutions and the former head of Pennsylvania's Department of Environmental Protection and the White House Council on Environmental Quality during the Clinton administration. "We didn't come to any conclusion that the deck chairs need to be shuffled around."

The group released an interim report in August that drew criticism from both industry and environmental groups for its conclusions that many of the environmental and health concerns that have been raised about shale gas drilling are valid and that regulators lack "effective control" over the drilling process.

The group is planning to expand on its recommendations and conclusions in a more detailed report due out in about six weeks.

The report and hearing come amid growing concerns about the hydraulic fracturing production technique that is used to extract hydrocarbons from compact rock formations by blasting them with a mixture of sand, water and chemicals. Environmentalists have raised concerns that the process, which industry has used for decades and says is safe, could taint water supplies.

But the panelists testifying yesterday said other aspects of the shale gas drilling boom -- like surface leaks and spills and well blowouts -- deserve further scrutiny as well.

"Hydraulic fracturing has become a bumper sticker," Stanford University geophysicist Mark Zoback told the committee. "There are significant environmental impacts to shale development, but none of them have anything to do with hydraulic fracturing."

Sen. Jeff Bingaman (D-N.M.), the committee's chairman, also stressed the importance of tracking greenhouse gas emissions from shale drilling activities now that some researchers have claimed shale gas could have a heavier climate footprint than other fossil fuels because of high levels of methane emissions at well sites.

"Some experts have claimed that fugitive emissions from natural gas extraction are routinely high enough that switching to natural gas could actually be worse than continuing to use coal," Bingaman said. "If natural gas is to be used as a lower carbon alternative to other fossil fuels, the issue of fugitive emissions is one that we must quantify, understand more fully and address appropriately."

The DOE panel largely dismissed those concerns in the August report, noting that the researchers' conclusion is "not widely accepted" and that more data are needed.