The program, authorised under Section 702 of the Foreign Intelligence Surveillance Act, allows US spy agencies to eavesdrop on and store vast amounts of digital communications from foreign suspects living outside the United States. It will expire on December 31 if Congress does not act.
"We have personally reported to our Presidents - Republican and Democratic - and to the Congress details of plots disrupted based on information from Section 702," the former intelligence chiefs said in letters to congressional leaders that were seen by Reuters.
"We strongly urge the Congress to reauthorize the program and continue allowing the intelligence community to protect our country," they wrote.
The letter's signatories include former directors of US national intelligence, the CIA and the National Security Agency; and a former attorney general.
Rights groups, including the American Civil Liberties Union, oppose the law in its current form because it sometimes incidentally collects communications of Americans. Those communications can then be subject to searches without a warrant by the Federal Bureau of Investigation for criminal and national security investigations.
The Senate Intelligence Committee is expected to privately vote on Tuesday on a bill to reauthorize Section 702 that privacy advocates say will largely lack their reform priorities.
Senator Ron Wyden, a Democratic member of the panel, sent a letter on Monday urging committee leaders to allow a vote to take place publicly, saying the bill "will have enormous impact on the security, liberty, and constitutional rights of the American people" and should be debated in the open.
A bipartisan group of lawmakers in the House of Representatives earlier this month introduced legislation intended to install new privacy protections for 702 surveillance, including a partial restriction on the FBI's ability to access American data that would require agents obtain a warrant when seeking evidence of a crime.
The former spy chiefs' letter was sent to the Republican and Democratic leaders of the Senate and House, and heads of the Senate and House Intelligence and Judiciary committees.
Implementation of the Section 702 program, they wrote, has received positive reviews from the independent Privacy and Civil Liberties Oversight Board.
The letter was signed by former directors of national intelligence Dennis Blair, James Clapper and Mike McConnell; former attorney general Michael Mukasey; former CIA director John Brennan; former NSA chief Keith Alexander; and Michael Hayden, who led both the CIA and the NSA.
(Reporting by Warren Strobel and Dustin Volz; editing by Grant McCool)