Congress could vote this week on legislation that would conclude a three-year battle to rewrite the nation’s electronic surveillance rules after congressional leaders and the Bush administration reached an agreement in principle, sources familiar with negotiations said.

Aides and officials worked to fine-tune the details of their rewrite of the Foreign Intelligence Surveillance Act, or FISA (PL 95-511), over the weekend, and did not anticipate a final agreement on the language before this week, when the House and Senate might take up the overhaul.

Past preliminary deals on FISA have fallen through, largely because the parties had agreed on what the law should do but disagreed on whether the specific language would achieve that goal.

In addition, some sources disputed that all sides were as close as others claimed, noting that some key lawmakers had not yet signed off on the compromise.

Since the administration’s secret warrantless surveillance program was revealed in 2005, Congress has been at the center of one of the most contentious post-Sept. 11 battles between national security proponents and civil liberties advocates.

The debate spawned by the program’s disclosure resulted in lawsuits, a massive lobbying war, sharp divisions between Republicans and Democrats, and divisions within the parties themselves.

The prospective deal was hammered out at a June 13 meeting that included House Majority Leader Steny H. Hoyer, D-Md., Senate Intelligence Vice Chairman Christopher S. Bond, R-Mo., panel Chairman John D. Rockefeller IV, D-W.Va., House Minority Whip Roy Blunt, R-Mo., and representatives from the Bush administration.

“A lot of progress was made on a terrorist surveillance bill that enables this critical program to go forward while protecting the privacy rights and civil liberties of Americans,” said Shana Marchio, Bond’s spokesperson, in a June 13 statement.

Absent from the meeting were the top two party leaders in the Senate, Majority Leader Harry Reid, D-Nev., and Minority Leader Mitch McConnell, R-Ky., and the top two party leaders in the House, Speaker Nancy Pelosi, D-Calif., and Minority Leader John A. Boehner, R-Ohio. It was unclear whether they have signed off on the prospective accord.

Under the tentative agreement, a major sticking point until now would be resolved by a compromise that would allow a federal district court — not the secret FISA court — to decide about providing retroactive legal immunity to telecommunications companies being sued for their role in the Bush administration’s warrantless surveillance program.

It was not immediately clear, however, what standard the court would use to determine whether such immunity was justified.

If that standard is too low, immunity opponents maintain, the law will have been written so that companies are virtually guaranteed immunity — devaluing any claim of court scrutiny.

One source said that 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.

A Senate Intelligence Committee report on an earlier version of the legislation detailed how the companies had received such assurances from the Justice Department and the White House.

Sources said that under the prospective deal, 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, and the intelligence community could begin its warrantless surveillance program before the FISA court review in “exigent,” or urgent, circumstances.

The sources declined to discuss other aspects of the compromise, such as when the legislation would sunset.

The fight over FISA began in late 2005, when The New York Times revealed the existence of the administration’s warrantless surveillance program. The Republican-controlled Congress was unable to work out a final FISA bill and send it to Bush’s desk.

The administration began pressing in the spring of 2007 for an update of the law that would expand its surveillance authority under FISA and include retroactive immunity for the sued telecommunications providers.

Approximately 40 lawsuits have sprung up in response to the program.

In August, Democrats reluctantly enacted a temporary law (PL 110-55) that gave Bush more spying powers but sidestepped the retroactive immunity question.

Since then, the House has passed two versions of the legislation (HR 3773), and while Republicans opposed both in favor of a Senate-passed, White House-favored bill, they began negotiating with Democrats in April.

The American Civil Liberties Union, which has been closely following the negotiations over the bill, issued a blistering statement June 13, portraying the compromise as a veiled version of the Senate-passed measure.

“This FISA deal looks like the unconstitutional Senate bill in sheep’s clothing,” said Caroline Fredrickson, director of the ACLU’s Washington legislative office.

“Whatever silk purse Hoyer tries to make of Bond’s sow’s ear, and no matter how they try to sell it, the end result of all this negotiating will be exactly what the administration has wanted from the beginning: FISA rewritten to delete court oversight of surveillance and immunity for its pals at the telephone companies,” Fredrickson said.