If the House of Representatives passes a stringent new surveillance bill tomorrow as expected, it may be in part thanks to a whistle-blower.

Late last week, conventional wisdom said that the House wouldn’t stand firm against an effort by big telecommunications companies and the Bush administration to forgive the telcos for any violations of law they committed while assisting with a top secret domestic surveillance program.

But that apparently changed after the whistle-blower group Government Accountability Project made public the assertion by security expert Babak Pasdar that he had once discovered a high-speed data line that may have been a part of a domestic spying program.

Dubbed the “Quantico Circuit,” the line was capable of piping massive quantities of Americans’ conversations and messages to an unknown recipient from a telecommuncations hub in New Jersey.

Neither the identity of the telco nor of the destination of the line have been confirmed. Pasdar would not identify the telco in question, but a 2006 lawsuit whose allegations match his claims named the carrier as Verizon. The company has declined comment on the allegation. In a court filing, it asked a judge to transfer the 2006 suit and combine it with a host of others filed against it and other telcos for their alleged involvement in government spying. The judge agreed.

Pasdar’s claims prompted a strong call for greater oversight from a powerful senior House Democrat.

“[O]ur attempts to verify and investigate” Pasdar’s claims have been “blocked at every turn by this administration,” charged House Energy and Commerce Committee Chairman John Dingell, D-Mich., in a letter to other lawmakers. Dingell, whose committee oversees the telecommunications industry, urged his colleagues not to vote “before they have sufficient facts.”

That letter “made people very leery of giving people blanket immunity when we don’t even know what they’re doing,” said Lisa Graves of the Center for National Security Studies, a Washington, D.C.-based civil liberties watchdog which has followed the legislation closely.

Since then, the tide appears to have turned in the House, and observers believe Democrats now have the votes to pass the bill as it stands — without language that would retroactively immunize telcos for cooperating in what the White House has called the Terrorist Surveillance Program.

Phone companies have sought such protections because they face dozens of civil suits from people who believe the phone companies assisted government domestic surveillance efforts. Last month the Senate passed a bill which included retroactive immunity. The Bush administration has called the bill “unacceptable,” and charged that it “would not provide the Intelligence Community the critical tools needed to protect the country.”

The House bill includes language its sponsors believe would encourage those suits to move forward, by allowing the telco defendants to share highly-classified evidence with the judge hearing the cases.

The bill also requires an audit of domestic surveillance efforts that would result in a public report late next year, as well as a congressional commission to investigate the same programs.

“This bill has some substantial steps towards…finding out what happened,” said the American Civil Liberties Union’s Michelle Richardson. Her organization has been supportive of the House bill.