As required by law, the NSA will end its wide-ranging surveillance programme by 11:59pm EST Saturday (4:59am GMT Sunday or 10:29am IST) and expects to have the new, scaled-back system in place by then, the White House said.
The transition is a long-awaited victory for privacy advocates and tech companies wary of broad government surveillance at a time when national security concerns are heightened in the wake of the Paris attacks earlier this month.
It comes two and a half years after the controversial programme was exposed by former NSA contractor Edward Snowden. The move, mandated by a law passed six months ago, represents the greatest reduction of US spying capabilities since they expanded dramatically after the September 11, 2001 attacks.
Under the Freedom Act, the NSA and law enforcement agencies can no longer collect telephone calling records in bulk in an effort to sniff out suspicious activity. Such records, known as "metadata," reveal which numbers Americans are calling and what time they place those calls, but not the content of the conversations.
Instead analysts must now get a court order to ask telecommunications companies like Verizon Communications to enable monitoring of call records of specific people or groups for up to six months.
"The act struck a reasonable compromise which allows us to continue to protect the country while implementing various reforms," National Security Council spokesman Ned Price said.
Some Republican lawmakers want to preserve bulk collection until 2017, citing the Nov. 13 Paris attacks in which 130 people died. The Islamic State has claimed responsibility for the killings.
But any new surveillance measures are unlikely to become law ahead of the November 2016 presidential elections.
A presidential review committee concluded the surveillance regime did not lead to a single clear counterterrorism breakthrough that could be directly attributed to the programme.
Metadata collected by the NSA over the past five years will be preserved for "data integrity purposes" through February 29, the White House said.
After that the NSA will purge all of its historic records once pending litigation is resolved.
© Thomson Reuters 2015