When the Department of Homeland Security wants advice on how to guard against terrorist attacks at chemical plants, it relies heavily on a special agency panel focused on the topic.

There's just one problem, critics say: The committee is stacked with more than a dozen chemical corporation lobbyists and other industry representatives, who have worked to water down agency standards and oppose tougher security requirements.

The Chemical Sector Committee, which also includes government officials, does most of its business in secret and is not covered by White House ethics rules aimed at curbing the influence of lobbyists in government.

"These are the same people that are lobbying on the Hill to kill stronger regulations," said Rick Hind, legislative director for the Greenpeace Toxics Campaign, which has asked DHS to broaden the committee's membership. "It's a very monopolistic lobbying opportunity."

The arrangement underscores the ongoing efforts of the chemical industry to limit oversight by DHS,which has struggled to enact security regulations for petroleum plants, chlorine factories and other facilities at risk for terrorist attacks.

The debate comes amid growing concerns over the ability of al-Qaeda and other terrorist groups to exploit gaps in the nation's security apparatus. Earlier this month, DHS tightened security for cargo shipments from abroad after the discovery of a Yemen-based plot to send bombs in shipped packages; the air-cargo industry had resisted such steps for years.

With chemical plants, critics complain that DHS has bowed to industry pressure on numerous fronts, ranging from which facilities can be inspected to what they can be required to do. DHS officials defend their record and say cooperation with industry groups is vital in order to make security plans work.

DHS spokesman Chris Ortman said the agency's assessment program "has already been effective in bringing about security improvements." About 7,000 chemical sites have been identified as high-risk, and more than 2,000 have taken steps to reduce risk factors, he said.

Rand Beers, undersecretary for the National Protection and Programs Directorate, wrote in a Nov. 2 letter to Greenpeace that the goal of such panels is to "help facilitate unfettered communication and coordination," and that the agency would work to include environmental groups and others in deliberations.

The issue of chemical-plant safety is under debate in Congress, where lawmakers are weighing whether to renew funding for the DHS reporting-and-inspection program. The House has voted to give regulators the power to require safer practices at chemical plants, but the idea has foundered amid industry opposition in the Senate.

Chemical industry groups argue that additional oversight is unnecessary and will cost jobs at a time of economic distress. The sector has spent nearly $40 million on lobbying since 2009, according to disclosure records.

"We are longtime advocates for chemical security regulations, but of course there is disagreement and debate about how that gets done," said Scott Jensen, spokesman for the American Chemistry Council, the industry's main lobbying group. "There's a lot at stake for our industry and our members."