President Barack Obama is expected to order the National Security Agency (NSA) to stop storing data from Americans’ phones, after a series of leaks about intelligence operations.
Reports suggest Mr Obama will ask Congress to arrange how the data is stored, and how agencies can access it.
The president is due to announce a number of changes to the spying system.
Former intelligence worker Edward Snowden has leaked an array of details about the NSA’s spying programme.
He is wanted for espionage in the US and now lives in exile in Russia.
The latest revelations claim that US agencies have collected and stored almost 200 million text messages every day across the globe.
An NSA programme called Dishfire extracted and stored data from the SMS messages to gather location information, contacts and financial data, according to the Guardian newspaper and Channel 4 News.
The information was shared with the UK’s spy agency, GCHQ.
Both agencies have defended their activities, saying they operate within the constraints of the law.
FISC shakeup
While he initially defended US surveillance practices, Mr Obama said in August that the US “can and must be more transparent” about its intelligence gathering.
In Friday’s speech, scheduled to take place at the Department of Justice at 11:00 (16:00 GMT), he is expected to approve a number of recommendations made by a panel that the White House commissioned last year.
Senior officials said the centrepiece of the reforms, if approved, will be the order to stop the NSA from storing information about Americans’ phone calls.
Storage of the data will instead fall to firms or another third party where it can be queried under limited conditions.
It will be a programme that “preserves the capabilities we need without the government holding this bulk metadata”, one official told AFP news agency.
Mr Obama is expected to leave the decision as to how that is implemented to Congress and the intelligence community.
Another proposal likely to be approved is the creation of a public advocate position at the Foreign Intelligence Surveillance Court (FISC), where government agencies request permission for mass spying programmes.
Currently, only the US government is represented in front of FISC judges.
Mr Obama is also expected to extend some privacy protections for foreigners, increase oversight of how the US monitors foreign leaders, and limit how long some data can be stored.
In late 2012 it was revealed that the US had spied on the communications of several foreign allies, including monitoring the personal mobile phone of German Chancellor Angela Merkel.
‘More confidence’
It is unclear whether Mr Obama’s speech will make any reference to Mr Snowden, who is hailed as a hero who should be pardoned by civil liberties groups, but whose actions many believe put lives in danger.
White House spokesman Jay Carney said on Thursday the aim was to make intelligence activities “more transparent”.
He said this would “give the public more confidence about the problems and the oversight of the programmes”.
The White House also said Mr Obama had briefed UK Prime Minister David Cameron on the review of NSA activities.
