The battle in the Senate over how to amend the Foreign Intelligence Surveillance Act (FISA) begins on Monday when, over the objections of prominent Democrats, Majority Leader Harry Reid will introduce the White House–supported version of a reform bill approved in October by the Senate Select Committee on Intelligence.

This past Tuesday, fourteen Democratic senators—including presidential contenders Hillary Clinton, Barack Obama, Joseph Biden, and Chris Dodd—signed a letter urging Reid to instead bring to the floor an alternative bill produced in November by the Judiciary Committee. That version of the legislation, which will now be offered as an amendment to the Intelligence Committee's bill, contained a variety of additional restrictions and checks on government wiretaps sought by civil liberties groups. It also, crucially, omitted a provision granting telecom companies retroactive immunity from lawsuits related to their cooperation with the president's extrajudicial eavesdropping program. President Bush has pledged to veto any FISA amendment that failed to provide such immunity—a threat that did not deter the House from passing just such a bill last month. Meanwhile, Senator Dodd, whose attempt to place a "hold" on the Intelligence Committee bill was overridden by Reid, is pledging to filibuster any legislation that does include retroactive immunity.

While Democrats have struggled to counteract a frustrated base's perception of congressional capitulation to the White House, the executive branch has mounted a full court press in favor of its preferred version of the law. In a Los Angeles Times op-ed on Wednesday, Attorney General Michael Mukasey warned that the changes made in the Judiciary Committee's version of the bill "would have the collective effect of weakening the government's ability to effectively surveil intelligence targets abroad." And on Thursday, Mukasey and Director of National Intelligence Mike McConnell made their case directly to the Senate in a closed-door briefing.

With divisions sharp, various attempts to split the difference between the alternatives have fallen flat. Reid had earlier sought, under the Senate's Rule Fourteen, to offer a pair of his own bills mixing and matching provisions from the two committees, a solution that appears to have pleased nobody. And on Thursday, the Judiciary Committee rejected a proposal by Senator Arlen Spector to allow lawsuits against the telecom companies to go forward, but with the government substituted as the defendant. (The groups bringing the suits worry that the government would be able to invoke legal defenses, such as executive privilege and sovereign immunity, that are unavailable to private telecom providers.) Michelle Richardson, a legislative consultant for the American Civil Liberties Union, hopes that this may be a strategic blunder on the administration's part. "A lot of people would probably support giving the government broader authority if they would decouple that issue from the immunity question," says Richardson, "so they're probably shooting themselves in the foot by forcing it to go forward like this."

The current wrangling continues a debate that began this summer with the hasty passage of the Protect America Act in response to a ruling by the FISA court—a ruling which the court has declined to release, but which is purported to have required intelligence agencies to acquire warrants when wiretapping conversations between foreign parties that were routed (and recorded) through US telecom switches. Eavesdropping on purely foreign communications had previously been unrestricted—primarily because, traditionally, the physical tap on foreign-to-foreign calls had occurred overseas, outside US jurisdiction. But the Protect America Act, which is due to expire in February, went beyond merely closing this "intelligence gap" and authorized a broad program of surveillance, under minimal court oversight, that permits Americans' conversations with foreigners to be collected, so long as the American party to the communication was not "targeted" by an investigation. The bills now under consideration seek to establish a more permanent solution: the Intelligence Committee version of the FISA Amendment would remain in effect for six years, while the Judiciary Committee version sunsets in four.

While media attention has focused largely on the question of immunity for telecom firms, the additional limitations on surveillance contained in the Judiciary Committee's version of the bill are, arguably, at least as significant. That bill would explicitly bar "bulk" or "vacuum cleaner" surveillance of international telecom traffic that is not directed at a particular person or telephone number. It would require individualized FISA court review whenever the collection of an American's communications became a "significant purpose" of an investigation, whether or not that person was a "target" of the investigation. And it would provide for a congressional audit of past extrajudicial surveillance by the National Security Agency.

A spokesman for Reid says the majority leader hopes to be able to send a bill to conference before Congress adjourns for winter recess, though some observers find this unlikely, and civil liberties groups are anxious to avoid a repetition of the sort of last-minute legislation that produced the Protect America Act. Meanwhile, some civil libertarians are already casting an eye toward the next battle. "We're going to keep fighting to get the important judicial protections in, the immunity out, but if we can't do those things we're going to get as many no votes on the final product as possible," says the ACLU's Richardson. "We don't want the members owning this bill, owning this program, so that when it finally does sunset we can get meaningful changes."