Civil rights campaigners voiced dismay on Friday over the US Senate's re-authorization of the government's warrantless surveillance program, and the defeat of two amendments that would have provided for basic oversight of the eavesdropping.

The Senate voted 73-23 to extend the law, called the Foreign Intelligence Surveillance Act Amendments Act, for five years. The House of Representatives has already passed the measure, which President Obama has said he will sign.

But while the program was extended as expected, campaigners saw a silver lining in that the vote was closer than when the legislation was first introduced in 2008.

"We're incredibly disappointed, not just that it passed, but that they rejected some very moderate amendments that wouldn't have interfered with the collection of intelligence," said Michelle Richardson, an ACLU expert on surveillance issues.

An amendment by senator Jeff Merkley of Oregon would have required the secret court that oversees surveillance requests to disclose "important rulings of law." It failed 37-54. An amendment by Merkley's fellow Oregon Democrat Ron Wyden would have required the government to estimate the number of US citizens it had spied on. It fell by a narrower margin, 43-52.

"We're actually pleased that so many [Senate] members today want more transparency," Richardson said, pointing to the 43 votes for Wyden. "There were more members voting for transparency and accountability than there were in 2008. The amendments did better this time."

The amended FISA Act was passed in 2008 to retroactively cover Bush-era domestic surveillance. The law permits the National Security Agency to track communication between foreign targets and people inside the United States without obtaining a warrant. Critics say it violates fourth amendment protections against unreasonable searches and seizures. NSA whistleblower Bill Binney has estimated that the agency, under protection of the law, has "assembled" 20 trillion transactions between US citizens.

Intelligence Committee chairwoman Dianne Feinstein, a Democrat from California, said in debate on the Senate floor that the surveillance program provides useful intelligence and does not target US citizens. She opposed both oversight amendments but agreed in principle to release unclassified summaries of actions taken by the secret court.

The Obama administration has already begun reviewing FISA court decisions to see what can be released, Richardson said.

"I think we have a long and slow fight on this, but we'll eventually get there," Richardson said.