A presidential advisory panel says telephone information collected in bulk by the National Security Agency and used in terror investigations "was not essential to preventing attacks" and has proposed sweeping changes to US government surveillance programmes.
Under the proposals, court orders would be also required before the information could be searched.
In a 300-page report, the five-member panel also proposed greater scrutiny of decisions to spy on friendly foreign leaders, a practice that has outraged US allies around the world.
While the panel's 46 recommendations broadly call for more oversight of the government's vast spying network, few programmes would be ended. There is also no guarantee that the most stringent recommendations will be adopted by President Barack Obama, who authorised the panel but is not obliged to act on its findings.
The task force said it sought to balance America's security with the public's privacy rights and insisted the country would not be put at risk if more oversight was put in place.
"We're not saying the struggle against terrorism is over or that we can dismantle the mechanisms that we have put in place to safeguard the country," said Richard Clarke, a task force member and former government counter-terrorism official. "What we are saying is those mechanisms can be more transparent."
The review group was set up amid the White House's response to leaks from former NSA contractor Edward Snowden about the scope of the government surveillance programmes.
Mr Snowden is now a fugitive from US authorities and was granted temporary asylum by Russia. The White House is conducting its own intelligence review, and Mr Obama is expected to announce his decisions in January.
The White House planned to release the panel's report next month, but officials said they decided to make it public now to avoid inaccurate reporting about its content.
It coincided with increased political pressure on Mr Obama following a blistering ruling from federal judge Richard Leon , who declared on Monday that the NSA's vast phone data collection was probably unconstitutional.
The judge called the NSA's operation "Orwellian" in scale and said there was little evidence that its gargantuan inventory of phone records from American users had prevented a terrorist attack. But he stopped his ruling from taking effect, pending a likely government appeal.
The panel's most sweeping proposal would terminate the NSA's ability to store the telephone data and instead require it to be held by the phone companies or a third party. Access to the data would then be permitted only through an order from the Foreign Intelligence Surveillance Court.
"With regard to the bulk metadata of phone calls, we think there should be judicial review before that information is accessed, and we don't think the government should retain it," Mr Clarke said.
If both recommendations were enacted, it is likely that they would slow down the intelligence collection process. The panel's recommendations allow for exceptions "in emergencies", leaving open the possibility of intelligence agencies scanning the information quickly and asking for permission later if they suspect imminent attack.
The task force did not say how long the phone companies would be required to hold the private data. The companies' retention policies vary markedly, according to information recently provided to the Senate Commerce Committee, ranging from one year at Verizon and US Cellular to five years at AT&T and seven to 10 years at T-Mobile.
AT&T and Verizon declined to comment on the report and its recommendations and T-Mobile said it would look closely at the proposals.
Another major shift recommended by the task force would tighten the use of so-called national security letters, which give the government sweeping authority to demand financial and phone records without prior court approval in national security cases.
The task force recommended that authorities should be required to obtain a prior "judicial finding" showing "reasonable grounds" that the information sought was relevant to terrorism or other intelligence activities.
The panel also tackled the diplomatic furor over NSA spying on the leaders of allied nations, including Germany. The group recommended that such spying be approved by the highest levels of government and that the decisions be based in part on whether the United States shares "fundamental values and interests" with the leaders of those nations.
The UN General Assembly unanimously adopted a resolution yesterday aimed at protecting the right to privacy against unlawful surveillance. Germany and Brazil introduced the resolution, which is legally non-binding, following a series of reports of US eavesdropping abroad, including on Brazilian president Dilma Rousseff and German chancellor Angela Merkel.
The report was issued a day after a group of top executives from leading technology companies met Mr Obama at the White House to discuss NSA surveillance and other issues. Several of the companies, including Facebook, Yahoo, Apple, Twitter and Microsoft, have joined to urge Obama to curb the surveillance programmes.
In a joint statement the companies praised the "thoughtful and transparent" approach taken by the White House panel in the report. "We look forward to a continued dialogue with the White House as we advocate for meaningful reform of government surveillance practices," they said.