Former CIA Director Michael Morell is seen November 28, 2012 in the Senate Visitors Center of the US Capitol in Washington

Telephone "metadata" controversially scooped up by a US intelligence agency should not be destroyed but stored by private telecom giants, a former CIA chief said Tuesday days before President Barack Obama announces new reforms.

Former Central Intelligence Agency acting director Michael Morell testified before the US Senate with the four other members of a committee Obama appointed to propose reforms.

Their report, published in December, recommended 46 changes.

"The program only has to be successful once to be invaluable," Morell told lawmakers, adding that the National Security Agency's deeply divisive program "does carry the potential going forward to prevent a catastrophic attack on the United States."

Last month, experts called for the program, which allows the NSA to store five years of data on all US calls—including numbers dialed and time and duration of calls, but not content of conversations—to be amended to improve transparency and prevent future abuse.

According to the experts, the storage of such data should be held by telecommunication operators and not on NSA servers.

Under such reforms, the NSA would have access to the data only after validation by a judge.

Women use their cellphones on January 7, 2014 in Los Angeles, California

"The concerns of our constitutional history is that government can do far more harm if it abuses the info in its possession than the private entities can," said Geoffrey Stone, a law professor and constitutional expert at the University of Chicago.

Should government maintain the data, "there's always the possibility of someone coming along, down the road, seeing this as a great opportunity to get political dirt on individuals, on their activities, their organizations, their associations," Stone said.

"That's a danger we want to avoid."

The Obama administration, like that of president George W. Bush before it, believes the metadata storage is not a violation of privacy since conversations are not recorded.

But Morell said the boundary "between metadata and content" remains tenuous.

"When you have the records of the phone calls that a particular individual made, you can learn an awful lot about that person," he told lawmakers.

Obama is set to make a speech Friday outlining his paths to reform the surveillance programs, which were the subject of months of international criticism after fugitive intelligence contractor Edward Snowden revealed the depths of the programs in June.

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© 2014 AFP