The Senate narrowly voted Tuesday to advance a bill to extend a powerful government authority to conduct foreign surveillance on U.S. soil, after leading Democrats joined senators opposing the legislation for not providing better protections for Americans.

The 60-to-38 vote barely cleared a procedural threshold for moving the bill toward a vote on final passage later this week, which would send to the president's desk the measure reauthorizing the National Security Agency's ability to collect from U.S. companies the emails and other communications of foreign targets located overseas.

Senate Intelligence Committee Chairman Richard Burr (R-N.C.) referred on Tuesday to the program, known as Section 702 of the Foreign Intelligence Surveillance Amendments Act of 2008, as "the single most important national security tool we have."

But privacy advocates have long railed against the program for putting little or no restrictions on federal law enforcement agencies' ability to query the database of Section 702 communications for information about Americans who may have been in touch with foreigners under surveillance. The bill on offer, which passed the House last week, requires law enforcement to obtain a court order before viewing the content of searches for Americans' information, if they intend to use it as evidence in a criminal case. But privacy advocates believe those steps do not go far enough, and they are pushing instead to require warrants to access the information in question.

Senate Minority Leader Charles E. Schumer (D-N.Y.) appeared to sympathize with the opposition on Tuesday, saying on the Senate floor that the measure "should go somewhat further" in balancing "legitimate concerns about privacy" with "the crucial national security imperatives of the program." He added that the pace with which the bill was slated to proceed through the Senate was "too quick for too much," considering that the measure extends the program for six years, noting "we ought to have some amendments and some discussion."

Senate leaders have not allowed votes on any amendments to the legislation on the Senate floor. Part of that is driven by the fact that Congress is working under a tight deadline: the statutory authority for the program formally expires Friday, though the intelligence community argues that even without an immediate reauthorization, the program can continue operationally until the spring.

Schumer's call left the Senate's vote in unexpected limbo for approximately 90 minutes, as leaders awaited the late arrival of Sens. John Neely Kennedy (R-La.) and Claire McCaskill (D-Mo.) to cast the decisive votes. Both voted in favor of advancing the measure, giving it the 60 votes needed to clear the procedural hurdle. The bill is expected to pass the full Senate late Wednesday or early Thursday and will be then sent to the president's desk.