Mr. Hale said the provision, which is recorded in federal statute books as a “transition procedures” note accompanying the main text of the law, makes it “very clear” that “any existing order will continue in effect for a short time even if Congress doesn’t act to reauthorize the law in a timely fashion.”

Given that conclusion, the government is making no plans to immediately turn off the program on New Year’s Day, no matter what happens in Congress, according to a United States official familiar with the Section 702 program who spoke on the condition of anonymity to discuss a sensitive topic.

The disclosure has significant ramifications for the debate over the program.

Congressional leaders have discussed including an extension of the program in other must-pass legislation, like a spending bill to keep the government from shutting down. But lawmakers will face less pressure to jam through such a move, short-circuiting a full and open debate over reform proposals, if the alternative is not an immediate termination of the collecting of intelligence authorized by the law.

Little consensus exists in Congress about what, if any, changes to make to the law as part of extending it. Lawmakers have submitted legislation spanning the gamut from making the law permanent without changes to imposing significant new limits to safeguard the privacy rights of Americans whose communications get swept up in the program, as well as a range of intermediary proposals.

One key disagreement centers on what limits, if any, to impose on how government officials may search for, gain access to or use in court information about Americans that gets swept into the warrantless surveillance program. Some lawmakers want to impose a broad provision forcing officials to get a warrant before they may query the repository about an American. Some want a more limited requirement that officials get a court’s permission to gain access to the results of such a query if it is for a criminal investigation but not a national security one. Some want to impose no new constraints.

Another major issue confronting lawmakers is what to say, if anything, about the N.S.A.’s old practice of collecting, from network switches on the internet’s backbone, international emails and other such messages that mention a foreigner who is a target of surveillance but are neither to nor from that person. The N.S.A. recently halted that practice but wants to retain the flexibility to turn it back on; some bills would codify a ban on it, and some would not.

The question of a Section 702 overhaul, and trade-offs between national security powers and privacy protections, has scrambled the usual party lines. Representative Robert W. Goodlatte of Virginia, the Republican chairman of the Judiciary Committee, has warned that legislation whose changes fall short of a compromise bill that he worked out with Democrats on his committee is unlikely to pass the House.