Democratic leaders of the House Energy and Commerce panel, citing new domestic spying claims, are urging careful examination of surveillance overhaul legislation that may delay progress on the measure.

Retroactive legal immunity to telecommunications companies being sued for helping with a government spying program is the major sticking point on legislation overhauling the Foreign Intelligence Surveillance Act currently in negotiations between the House and Senate.

In a letter to lawmakers Thursday, panel Chairman John D. Dingell of Michigan, and two subcommittee chairmen, Edward J. Markey of Massachusetts and Bart Stupak of Michigan, said claims by the chief of security at an unnamed wireless carrier that the company may have given a government entity access to all of its customers’ communications, justified further delay in considering the legislation.

“Because legislators should not vote before they have sufficient facts, we continue to insist that all House members be given access to the necessary information, including the relevant documents underlying this matter, to make an informed decision on their vote,” the trio wrote.

Babak Pasdar, chief executive of a security firm who was hired to upgrade security at the unnamed telecommunications company, said he discovered a third-party security breach traced to a governmental office in Quantico, Va., home to a U.S Marine Corps base and the FBI Academy, the letter said.

Pasdar’s allegations are similar to those of Mark Klein, a former AT&T technician whose claims support a lawsuit against the company being advanced by the Electronic Frontier Foundation, an internet privacy advocacy group.

Republicans have been pressing the White House-backed Senate version of the bill, which passed Feb. 12. The Senate version effectively authorizes warrantless surveillance with additional court oversight and grants retroactive immunity to private companies that cooperated.

The House version passed in November does not grant retroactive immunity and imposes tighter controls on surveillance. House leaders have refused to take up the Senate version, and the extent of the Bush administration’s surveillance initiatives has been a major concern in their decision.