“The House has acted; it’s time for the Senate to act,” Speaker John A. Boehner (R-Ohio) said Thursday. (Susan Walsh/AP)

The legal authority for a controversial National Security Agency surveillance program remained Thursday on a path to expiration, with key senators still divided on how to move forward as the Obama administration stepped up its lobbying for revisions to the program.

If the House and Senate do not act in concert by midnight May 31, the NSA’s bulk collection of telephone “metadata” from private companies will end, at least temporarily. The House passed a White House-backed bill last week reworking the program, keeping the records in private hands but allowing authorities to seek discrete records with a court order, but top Senate Republicans have balked, saying the changes­ could hamper counterterrorism efforts.

One of those Republicans, Intelligence Committee Chairman Richard Burr, floated a compromise late Thursday that would extend the transition to private storage to two years. But NSA Director Michael S. Rogers told Senate leaders that the six-month transition period in the House bill is adequate.

“We are aware of no technical or security reasons why this cannot be tested and brought on line within the 180-day period,” Rogers said in a letter obtained by The Washington Post.

Sen. Rand Paul (R-Ky.) took to the floor Wednesday afternoon to "filibuster" the renewal of the Patriot Act. Paul claims it gives government too much access to citizens’ private cell phone records. (C-SPAN)

In a further complication, the House took its final votes for the week early Thursday afternoon, with members jetting out of town soon afterward — some of them overseas on official delegations. With both chambers scheduled to recess until midday June 1, hours after current law is set to expire, options to prevent a lapse in surveillance authority have dwindled.

“The House has acted; it’s time for the Senate to act,” Speaker John A. Boehner (R-Ohio) said Thursday, repeating a week-old refrain on the subject.

Senate Majority Leader Mitch McConnell (R-Ky.) on Thursday started the process of closing debate on two bills related to the surveillance program: the House bill, known as the USA Freedom Act, and an extension of the current legal authority through July 31.

McConnell’s moves set up votes no later than Saturday on the two bills, but enough senators might oppose either the short-term extension or the House-passed reforms to leave matters in limbo.

Burr (N.C.), who has been an outspoken advocate for continuing the current authority, said he expected both test votes, requiring a 60-vote majority, to fail. He suggested that the Senate could pass a stopgap measure as short as five days to give both chambers time to act on his compromise bill and said he was not concerned that the House is now out of session.

“The biggest mistake you can make is to take somebody at face value up here,” he said. “If the best we can work out this weekend is . . . a short-term extension, I think the House would go along with that in an effort to try to get a win-win.”

Boehner left the door slightly ajar for further House action on surveillance, saying he would “certainly look at what [senators] do and make a decision about how to proceed.”

Senior administration officials have been briefing and calling senators this week and last week urging them to pass USA Freedom to avoid legal uncertainty around the NSA program and to ensure the government does not lose critical intelligence-gathering tools at a time of renewed fears of terrorist attacks.

Several senators attended a White House meeting Thursday with President Obama’s top homeland security adviser, Lisa Monaco.

“We’re concerned that people don’t understand the risk of doing anything other than passing the USA Freedom Act,” said a senior administration official not authorized to speak for the record in a conference call with reporters.

The administration’s full-court press also includes the directors of the NSA and FBI as well as senior officials from the Justice Department and Office of the Director of National Intelligence. “There’s been no dearth of effort to try and provide folks information and answer their questions,” the official said.

While the Senate floor remained tied up with complex and contentious trade legislation Thursday, most of Wednesday’s floor time was spent on surveillance, thanks to a 10 1/2 -hour floor speech by Sen. Rand Paul (R-Ky.), a presidential candidate and fierce critic of the NSA program disclosed in 2013 by former agency contractor Edward Snowden.

Paul, who believes the House bill does not go far enough to check potential government invasions of privacy, said he wanted an extended debate on the surveillance program and the opportunity to amend any legislation extending it.

Sen. John Thune (S.D.), the third-ranking Republican leader, said Thursday that it was possible that “maybe a couple” of amendments might be considered to the House bill, which might persuade skeptics to move forward with the legislation before Saturday.

But one of the sponsors of the Senate companion to the House bill, Patrick J. Leahy (Vt.), said he did not favor amendments. “I don’t support anything short of what the House passed,” the top Judiciary Committee Democrat said. “The choice is very simple: You take the House bill, or, because of the time running out, you end the whole Patriot Act.”