The Obama administration is warning that the FBI will lose legal tools critical to national security investigations at a time of heightened threats of terrorism if Congress fails to renew key USA Patriot Act provisions by midnight Sunday.

“What you’re doing essentially is you’re just playing national security Russian roulette,” a senior administration official said at a press briefing Wednesday. “That’s a game that you can play. But we urge Congress not to play that game with these uncontroversial authorities.”

Attorney General Loretta E. Lynch said Wednesday that a failure to act would cause “a serious lapse in our ability to protect the American people.”

The appeal came with four days to go before the expiration of three legal authorities, one of which — Section 215 of the Patriot Act — has been used to justify a controversial National Security Agency collection program that President Obama wants Congress to replace.

The administration is making a big push to try to sway public opinion as Sen. Rand Paul (R-Ky.), a presidential candidate, appears intent on taking a stand against mass surveillance that could well take Congress past a June 1 deadline to renew the authorities.

Sen. Rand Paul (R-Ky.), a presidential candidate, appears intent on taking a stand against mass surveillance that could well take Congress past a June 1 deadline to renew key USA Patriot Act provisions . (Carolyn Kaster/AP)

Paul in particular is opposed to the NSA program that collects large troves of “metadata” on Americans’ phone calls — numbers, times and durations — from phone companies for later search by intelligence analysts.

Obama also wants the NSA to end its mass data collection, but Paul wants to go further than the administration and says the bill that the White House has endorsed — the USA Freedom Act — lacks sufficient reforms. That bill passed the House this month by an overwhelming 338-to-88 margin. But the Senate on Saturday did not reach the 60 votes necessary to proceed to debate on the bill, and Majority Leader Mitch McConnell (R-Ky.) ordered members to come back from their Memorial Day recess a day early – this Sunday — to act on the issue just hours ahead of the midnight deadline.

The USA Freedom Act, a second senior administration official said, is “the only clear path” to end bulk collection, secure surveillance reforms and preserve the three authorities that national security officials say are crucial to terrorism and spy probes.

Lost in the public debate, the administration says, is the “noncontroversial” use of Section 215, to gather records on individuals, officials said. It is used in about 200 terrorism and spy investigations a year, they said. A second tool is the “roving wiretap,” which enables the FBI to use one warrant to wiretap a spy or terrorist suspect who is constantly switching cellphones. Those two in particular are of “tremendous value,” the first official said.

A third tool allows the FBI to surveil a “lone wolf” suspect who cannot be tied to a foreign terrorist group such as al-Qaeda. It has never been used, but officials said it is a valuable authority they do not want to lose.

The USA Freedom Act includes a six-month transition period during which collection would continue. After that, the idea is that the phone companies would push records to the NSA that are linked to individual terrorist suspects and the NSA bulk collection would end.

But even if Congress passes USA Freedom on Sunday, it is likely that a temporary lapse of collection will occur, the officials said. That is because the Justice Department will need to apply to a special surveillance court for a new order to collect data and that could take several days. The government would ask the Foreign Intelligence Surveillance Court to act quickly, the first official said. “But I think it’s reasonable to assume that at least you’re talking a three-to-four-day period to get this thing” authorized.

It is possible that the order could involve retroactive collection to cover the gap, the second official said.

If the Senate does not pass USA Freedom on Sunday, the NSA collection will shut down. It will take the agency eight hours to turn off servers that receive the metadata, a third senior official said.

The companies for their part will have to power off the systems that send the data, the official said.

The administration said that even if the authorities lapse, they will continue to push for passage of USA Freedom. “We think it’s the right compromise,” the second official said.

Officials expressed uncertainty about whether they could use a grandfather clause in the law to renew orders for existing national security investigations under individual Section 215 orders and using the roving wiretap authority. “I think we’re going to do an assessment, see where we are when they expire and then work to make appropriate arguments,” the first official said.

“What my colleague is illustrating here is that there’s doubt about that now,” the second official said. “There’s unnecessary risk that’s being put on these ongoing investigations because of the failure of Congress to act.”

Mike DeBonis contributed to this report.