Even if lawmakers reach an agreement, the program will lapse until legislation is approved by both the House and the Senate next week -- something administration officials said could pose a grave threat to Americans' safety.
A gap in the programs amounts to playing "national security Russian roulette," according to one official.
Unless reauthorized by Congress, the National Security Agency will have to shutter, at least temporarily, its bulk phone data collection program, which provides the intelligence community clues as to who potential terrorists are calling.
Another program that allows government surveillance of so-called "lone wolf" terrorists -- those not associated with a particular terrorist group -- would also be forced to stop operations.
Officials said Wednesday the "lone wolf" tracking provision has never before been used, but nonetheless provides an important option for monitoring suspected terrorists.
In addition, the government would not be permitted to get a roaming wiretap to track a terrorism suspect who regularly switches phones to avoid detection, a measure used less than 100 times per year, according to the officials.
"Without action from the Senate, we will experience a serious lapse in our ability to protect the American people," Attorney General Loretta Lynch warned on Wednesday.
"Today, I join the President in urging the Senate to work through the current recess in order to make sure that we can continue to appropriately safeguard this country and protect its citizens," she said.
It's too soon to know if a compromise can be brokered before Sunday, when the Senate returns from a one-week recess to work to try to pass something to keep the NSA and other programs from expiring.
The unusual Sunday session was needed after Sen. Rand Paul, R-Kentucky, Sen. Ron Wyden, D-Oregon, and Sen. Martin Heinrich, D-New Mexico, abruptly refused to allow even short-term extensions of the current law to pass.
Senate Republican leaders -- who pride themselves as being hawkish on national security -- are facing the reality that even if they come up with a broadly acceptable compromise that could pass each chamber, Paul and other opponents likely will use procedural hurdles to delay its passage. That means the programs could go dark for several days.
The authorities expire when the clock strikes midnight on Sunday night into Monday, June 1.
The Obama administration says it will need to begin winding down the surveillance programs before that time, beginning at 4 p.m. ET on Sunday when it will inform telephone companies to begin shutting down their bulk collection programs.
The NSA would also begin turning off its servers and reconfiguring software to comply with the lapse. By 8 p.m. ET on Sunday, the NSA would be unable to reverse the shutdown. Restarting the surveillance programs would take about a day, officials said.
Senate Majority Leader Mitch McConnell and Senate Intelligence Committee Chairman Richard Burr, R-North Carolina, are leading the effort to find a compromise on Capitol Hill. Both opposed the USA Freedom Act, which would modify current programs, that passed the House with overwhelming bipartisan support two weeks ago, but failed in the Senate by three votes. McConnell and Burr instead support a clean reauthorization of current data collection policies.
Backed by a broad coalition of civil liberties-minded liberal Democrats and conservative Republicans, the USA Freedom Act ends the government's authority to gather and hold massive amounts of data about phone calls placed by Americans every day. But it preserves the ability of intelligence officials who are pursuing a terrorism suspect to get a warrant from the U.S. Foreign Intelligence Surveillance Court to search the phone records that are held by the individual phone companies.
With lawmakers out of Washington and just days before the deadline at the end of the month, McConnell and Burr are talking individually and in conference calls with other senators. They are also emailing back and forth as they search for ways to tweak the House-passed bill to make it more acceptable to Republican senators who opposed it last week.
Others involved in the discussions include Sen. Chuck Grassley, R-Iowa, the chairman of the Judiciary Committee, and other members of the judiciary and intelligence committees, according to a GOP leadership aide.
"We'll be in on Sunday and we're endeavoring to get this done," said Don Stewart, top McConnell aide.
A bill introduced by Burr is similar to the USA Freedom Act but includes a longer transition time -- two years instead of 6 months -- for the government to stop collecting the bulk data and rely on the phone companies to hold the records instead. Burr says that is designed to ensure the technology the phone companies will use to store the data will work.
Despite the efforts of GOP leaders to broker a compromise, Senate supporters of the USA Freedom Act stressed this week that their bill is already a bipartisan compromise and has the best chance of being approved right away in the Senate.
They believe at least three more senators might vote for it now that the program faces extinction. The supporters are pouring over potential vote changers, including a batch of Republican senators up for re-election in 2016 from swing states such as Sen. Pat Toomey of Pennsylvania, Sen. Mark Kirk of Illinois, Sen. Roy Blunt of Missouri, Sen. Kelly Ayotte of New Hampshire, and Sen. Johnny Isakson of Georgia. They also consider Sen. Angus King, an independent of Maine who caucuses with the Democrats, as a potential new vote for the bill.
King, a member of the Intelligence Committee, has said he supports the thrust of the USA Freedom Act but wants some changes as it relates to retention of call records by the phone companies. He has co-sponsored a bill with Sen. Dianne Feinstein of California, the top Democrat on the Intelligence Committee, to do just that.
The House returns to work Monday, the first full day after the law lapses. House GOP leadership aides insist the ball is in the Senate's court to come up with a plan that can avoid a major shutdown of the NSA programs and pass muster in the House. There are no plans for the House to come back early.