The Senate was expected to begin debating whether to proceed to an overhaul of electronic surveillance rules Thursday, but a vote on the measure before the July Fourth recess remained uncertain.

Senators agreed Wednesday to limit debate on a motion to proceed to the legislation, meaning that for the next 30 legislative hours, the Senate will be debating the bill unless everyone agrees otherwise.

Despite the 80-15 vote to limit debate, Senate clearance of an overhaul of electronic surveillance rules could slip until after the recess as the chamber juggles other priorities and procedural snarls.

Late Wednesday, Senate Majority Leader Harry Reid, D-Nev., threatened to keep senators in through the weekend to work on several bills, including the spying legislation (HR 6304). Reid has often issued threats to keep senators through the weekend but rarely followed through on them.

Earlier in the day, Reid said clearing the legislation this week was less important than housing (HR 3221) and Medicare (HR 6331) legislation. The spying bill would rewrite the Foreign Intelligence Surveillance Act (FISA, PL 95-511).

Reid said Republicans have been holding up the housing bill, delaying final action on FISA legislation that the Bush administration favors. Reid appeared to be putting pressure on Republicans to cooperate on the housing bill if they wanted to clear the FISA legislation they support. But by the end of the day, Reid said the Senate could push consideration of the housing legislation into July.

Reid said that he still planned to move the FISA bill this week — even though he opposed it — because he has an “obligation” to act on a measure that has the support of the majority of senators. But Reid left open the possibility that the FISA vote could be delayed until July.

“I’m going to try to do that,” he said. “The only reason why I wouldn’t is . . . if we’re stuck on the housing thing and I can’t get to that.”

Reid said June 24 that his priorities before the recess were action on the housing and Medicare bills.

“We don’t have to do FISA and we don’t have to do the supplemental” spending measure for the wars in Iraq and Afghanistan (HR2642), he said.

Minority Leader Mitch McConnell, R-Ky., has said he is eager to “get all of those things done in the next few days.”

Senate liberals oppose the FISA bill because it would effectively grant retroactive legal immunity to telecommunications companies being sued for aiding the Bush administration’s warrantless surveillance program. They also argue that its court and congressional oversight provisions are not robust enough to defend the privacy of U.S. citizens whose communications with foreign spying targets may be monitored without a warrant under the legislation.

Democrats Russ Feingold of Wisconsin and Christopher J. Dodd of Connecticut said they intend to force procedural votes to delay the measure. Together with Sen. Barack Obama of Illinois, the presumed Democratic presidential nominee, they advocate for a vote on an amendment to remove the bill’s retroactive legal immunity provision. As of late Wednesday, there still was no agreement on what amendments would be considered.

Kathleen Hunter and Greg Vadala contributed to this story.