WASHINGTON - Barring a last-minute deal in Congress, three post-Sept. 11 surveillance laws used against suspected spies and terrorists are set to expire as Sunday turns into Monday.

Will that make Americans less secure?

Absolutely, Obama administration officials say.

Nonsense, counter civil liberties activists.

Even if senators set to meet in an unusual Sunday session agree to advance a House-passed bill that extends the programs, one lawmaker said he will use his right to delay a final vote and let the powers lapse once midnight arrives.

"We do not need to give up who we are to defeat" terrorists, said GOP Sen. Rand Paul of Kentucky, a 2016 presidential candidate. "There has to be another way," he said Saturday in a statement and on Twitter, pledging to force the expiration of an "illegal spy program."

While there are compelling arguments on both sides, failure to pass legislation would mean new barriers for the government in domestic national security investigations, at a time when intelligence officials say the threat at home is growing.

"If these provisions expire, counterterrorism investigators are going to have greater restrictions on them than ordinary law enforcement investigators," said Nathan Sales, a Syracuse University law professor and former Justice Department official in the George W. Bush administration.

Until now, much of the debate has focused on the National Security Agency's collection of Americans' telephone calling records. This collection was authorized under one of the expiring provisions, Section 215 of the Patriot Act. Independent evaluations have cast doubt on that program's importance, and even law enforcement officials say in private that losing this ability would not carry severe consequences.

Yet the fight over those records has jeopardized other surveillance programs that have broad, bipartisan support and could fall victim to congressional gridlock.

The FBI uses Section 215 to collect other business records tied to specific terrorism investigations. A separate section in the Patriot Act allows the FBI to eavesdrop, via wiretaps, on suspected terrorists or spies who discard phones to dodge surveillance. A third provision, targeting "lone wolf" attackers, has never been used and thus may not be missed if it lapses.

Government and law enforcement officials, including Attorney General Loretta Lynch and Director of National Intelligence James Clapper, have said in recent days that letting the wiretap and business records provisions expire would undercut the FBI's ability to investigate terrorism and espionage.

Lynch said it would mean "a serious lapse in our ability to protect the American people." Clapper said in a statement Friday that prompt passage by the Senate of the House bill "is the best way to minimize any possible disruption of our ability to protect the American people."

Obama used his weekly radio and Internet address Saturday to accuse opponents of hijacking the debate for political reasons. "Terrorists like al-Qaida and ISIL aren't suddenly going to stop plotting against us at midnight tomorrow, and we shouldn't surrender the tools that help keep us safe," he said, using an acronym for the Islamic State group.

Civil liberties activists say the pre-Sept. 11 law gives the FBI enough authority to do its job. To bolster their case, they cite a newly released and heavily blacked out report by the Justice Department's internal watchdog that examined the FBI's use up to 2009 of business record collection under Section 215.

"The government has numerous other tools, including administrative and grand jury subpoenas, which would enable it to gather necessary information," in terrorism investigations, the American Civil Liberties Union said in a statement.

Section 215 allows the FBI to serve a secret order requiring a business to hand over records relevant to a terrorism or espionage investigation. The FBI uses the authority "fewer than 200 times a year," Director James Comey said last week.

The inspector general's report said it was used in "investigations of groups comprised of unknown members and to obtain information in bulk concerning persons who are not the subjects of or associated with an authorized FBI investigation."

But from 2007 to 2009, the report said, none of that material had cracked a specific terrorism case.

"The agents we interviewed did not identify any major case developments that resulted from use of the records obtained in response to Section 215 orders," the report said.

The report analyzed several cases, but most of the details are blacked out. In some cases, the FBI agent pronounced the 215 authority "useful" or "effective," but the context and detail were censored.

In 2011, Bob Litt, the general counsel for the director of national intelligence, testified before Congress that the business records provision was used to obtain information "essential" in the investigation of Khalid Aldawsari, a 20-year-old Saudi-born resident of Lubbock, Texas, who was sentenced to life in prison for plotting to bomb American targets in 2011.

In another case, Litt said, "hotel records that we obtained under a business records order showed that over a number of years, a suspected spy had arranged lodging for other suspected intelligence officers." Those records gave the FBI the information it needed to get a secret national security eavesdropping warrant, he said.

Sunday's Senate session became necessary after the chamber failed to act before leaving town early on May 23 for a holiday break. The USA Freedom Act, which passed the House passed overwhelmingly, fell three votes short of the 60 needed to proceed in the Senate, and efforts to extend the current law also failed.

If the USA Freedom Act were to become law, the business records provision and the roving wiretap authority would return immediately. The NSA would resume collecting American telephone records for a six-month period while shifting to a system of searching phone company records case by case.

If no agreement is reached, all the provisions will expire.

A third possibility is a temporary extension of current law while lawmakers work out a deal, but House members have expressed opposition.