Sen. Mark R. Warner (D-Va.), the top Democrat on the Senate Intelligence Committee, speaks to reporters last week on Capitol Hill. (Zach Gibson/Bloomberg News)

The Senate Intelligence Committee this week advanced a bill that renews a powerful surveillance authority enabling the government to collect foreign intelligence on U.S. soil.

The 12-to-3 vote reflected divisions on the panel over whether and how to strengthen privacy protections in the law, known as Section 702 of the FISA Amendments Act. And it shows that a path to renewing the authority, which expires at the end of the year, is anything but clear in the Senate.

The National Security Agency calls the law its most important operational statute. The intelligence community would like to see it renewed without change. But that is unlikely to happen given strong opposition in the House.

Section 702 enables the NSA to collect from U.S. companies the emails and other communications of foreign targets overseas for intelligence purposes. Some of those communications may be with Americans, and civil-liberties advocates are concerned because the law does not require a warrant to search within the data for Americans’ information.

In an apparent attempt to address that concern, the Senate committee on Tuesday, during a closed session, agreed unanimously to impose a new procedural hurdle for the FBI to review and use Americans’ emails and other communications collected under the authority. But the measure, proposed by Sen. Mark R. Warner (D-Va.), the panel’s ranking Democrat, does not go as far as civil liberties advocates say is necessary.

It does not require the FBI to obtain a warrant before searching for Americans’ communications. Nor does it require the court to demonstrate that those Americans may be engaged in criminal activity or acting as agents of a foreign power.

Instead, it specifies that if an FBI query turns up information on “a known United States person,” it has one business day to submit a request to the Foreign Intelligence Surveillance Court, which hears applications for foreign surveillance in the United States. The court then has two business days to rule on the request’s legality, according to several people familiar with the measure.

Any request for a foreign intelligence or law enforcement purpose is legal under the secret court’s rulings. That means that virtually all requests would be approved, analysts said.

If the court rules against the request, investigators are barred from using the information “in any court proceeding.” But the provision applies only to queries that turn up data on “known” U.S. persons. There is no requirement to run queries that yield data on possible U.S. persons or about foreigner citizens.

“This is not reform,” said Elizabeth Goitein, co-director of the Liberty and National Security Program at the Brennan Center for Justice. “This is window dressing.”

Moreover, she said, the measure would greatly add to the surveillance court’s workload without any meaningful enhancement for Americans’ privacy.

A spokeswoman for Warner declined to comment.

The committee bill, which has not been made public, stands in contrast to a House Judiciary Committee proposal to renew Section 702 that would instead require the FBI to obtain a warrant, based on probable cause, to review any communications turned up in a query seeking evidence of a crime. It would not apply to queries for counterterrorism, counterproliferation or counterespionage purposes.

Before adopting Warner’s amendment, the committee rejected a measure from two California Democrats — Sens. Dianne Feinstein and Kamala D. Harris — that would have required the FBI to obtain a warrant before accessing the content of Americans’ emails. The move is noteworthy because Feinstein has been a staunch advocate of robust surveillance capabilities. Feinstein’s decision to join forces with Harris comes barely two weeks after Feinstein announced her intention to run for reelection to a fifth full Senate term.

FBI Director Christopher A. Wray was in Feinstein’s office Monday asking her not to offer the amendment. Intelligence officials have said that they do not think such a requirement is necessary or advisable.

Wray has said that the FBI receives information on 4.3 percent of the targets under NSA Section 702 collection. That translates to some 4,500 foreign targets. That is part of the data pool the FBI taps when doing its queries.

Sen. Ron Wyden (D-Ore.), a committee member and one of the Senate’s most vocal privacy advocates, has filed a bill with Sen. Rand Paul (R-Ky.) that would require the FBI to obtain a warrant before querying Section 702 data when investigators are looking specifically for Americans’ communications.

Wyden was one of three senators who voted against the overall bill on privacy grounds. Joining him were Harris and Sen. Martin Heinrich (D-N.M.).

A spokeswoman for Senate Majority Leader Mitch McConnell (R-Ky.) said that no scheduling decisions about the legislation have been made. Given the controversy, she said, the FISA bill is not expected to be sent to the Senate floor before senators outside the committee have a chance to weigh in.

Senate Judiciary Committee Chairman Charles E. Grassley (R-Iowa), for his part, said he was not expecting to take up the intelligence panel’s bill.

Should the legislation clear the Senate, it is unlikely to make it through the House, where a coalition of liberal Democrats and conservative Republicans — including many members of the Freedom Caucus — support stronger privacy protections in Section 702.