By Tim Starks, CQ Staff

Congressional leaders and the Bush administration have reached an agreement in principle on an overhaul of surveillance rules, sources familiar with negotiations said Friday.

Aides and officials were still fine-tuning the details of their rewrite of the Foreign Intelligence Surveillance Act (FISA, PL 95-511) and did not expect a final agreement on the language before next week, when the House and Senate are now likely to vote on the overhaul.

Past deals on FISA have fallen through when the parties agreed on what the law should do, but disagreed on whether the specific language achieved that goal.

According to sources familiar with the negotiations, the compromise would be very similar to the last proposal by Sen. Christopher S. Bond , R-Mo., to House Majority Leader Steny H. Hoyer , D-Md.

Sources said the major change is that a federal district court, not the secret FISA court itself, would make an assessment about whether to provide retroactive legal immunity to telecommunications companies being sued for their alleged role in the Bush administration’s warrantless surveillance program.

It was not immediately clear, however, what standard the court would use to determine whether retroactive legal immunity was justified. If that standard is too low, civil liberties advocates maintain, the law will have been written so that companies are almost assured of being granted immunity, and any claim of court scrutiny is a mirage. One source said the court would review whether there was “substantial evidence” that the companies had received assurances from the government that the administration’s program was legal.

Under the last version of the Bond proposal, the FISA court would get to review, in advance, the process by which the administration chooses foreign surveillance targets who may be communicating with people in the United States. No warrants would be needed in such cases, though, and the executive branch could begin its warrantless surveillance program before the FISA court review in “exigent,” or urgent circumstances.

One House Democratic aide familiar with negotiations said there were other major changes made to the Bond proposal.

Caroline Fredrickson, the Washington director of the American Civil Liberties Union, said that sources told the ACLU the deal would sunset after six years unless Congress renewed it.

The House Democratic aide said the sunset timetable was not six years, but declined to specify the length of time the law would remain in effect.

The deal was hammered out Thursday night at a meeting that included Hoyer, Bond, Senate Intelligence Committee Chairman John D. Rockefeller IV , D-W.Va., House Minority Whip Roy Blunt , R-Mo., and representatives from the Bush administration.