Dianne Feinstein, the chair of the US Senate committee charged with holding the intelligence establishment to account, declared on Monday that the National Security Agency’s mass collection of phone records is “not surveillance” and should be maintained as an essential tool to combat terrorism.

Feinstein made the case for retaining the program, which routinely collects and stores the phone records millions of Americans, in an op-ed for USA Today, in which she wrote that the NSA’s work had been “effective in helping to prevent terrorist plots against the US and our allies”.

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Feinstein, a Democrat from California, is introducing legislation that would make superficial alterations to the NSA and the secret courts that are supposed to provide judicial oversight.

But her bill stops short of making any substantial changes to the way the agency conducts its work, despite the string of revelations based on disclosures by the former NSA contractor Edward Snowden.

A host of rival bills being introduced in Washington go much further, including one from Democratic senator Patrick Leahy, who chairs the Senate judiciary committee. Leahy is proposing an end to the bulk collection of phone records, which is authorised under an interpretation of section 215 of the Patriot Act.

Leahy’s bill, which is viewed as the main rival to Feinstein’s, will be introduced simultaneously in the House by Republican Jim Sensenbrenner, the author of the Patriot Act. He has said the law was never intended for this kind of data collection, a program he now intends to put “out of business”.

Senior intelligence officials are lobbying hard on Capitol Hill to protect the program, and Feinstein has been one of their strongest supporters in Congress. In her op-ed, Feinstein repeated the testimony of NSA and other intelligence leaders, which many critics argue has been misleading.

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“The call-records program is not surveillance. It does not collect the content of any communication, nor do the records include names or locations,” Feinstein wrote. “The NSA only collects the type of information found on a telephone bill: phone numbers of calls placed and received, the time of the calls and duration.”

Several experts independent of the intelligence committee have testified, including to Feinstein’s committee, that the collection of phone metadata can provide a detailed and intrusive window into an individual’s life, particularly when matched with other data. A person’s name, for instance, can easily be derived from their telephone number.

However, Feinstein said that it was necessary for the agency to obtain “the haystack” of phone records in order to find the terrorist “needle”.

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“To be effective, the NSA must be able to conduct these queries quickly, without regard to which phone carrier a terrorist or conspirator uses,” she said. “And the records must be available for a few years – longer than phone companies need them for billing purposes.”

Feinstein also advanced another controversial claim that has been repeatedly challenged by other senators, including Leahy, when she said the phone record collection program had “played a role in stopping roughly a dozen terror plots”.

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In their committee roles, Leahy and Feinstein have been given privileged access to classified information about the cases when the program has been used. Leahy has argued that the usefulness of the program has been exaggerated by the intelligence community.

“The American people are getting left with inaccurate reflection of the NSA’s programs,” he said during a committee hearing earlier this month. Under questioning from Leahy during that session, the director of the NSA, Keith Alexander, admitted there were only “one or possibly two” cases of terrorist activity that would not have been prevented “but for” section 215 of the Patriot Act.

In July, an amendment introduced in the House of Representatives to end the dragnet collection of phone records was narrowly defeated, falling just 12 votes short of passage. Justin Amash, the Republican who co-authored that measure, recently told the Guardian that opposition to the program has “solidified” in recent months.

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Amash attributed the hardening of opposition to members of Congress returning to their districts, where they heard complaints from constituents angry about their records were being stored, and to the succession of revelations, published in the Guardian, the Washington Post and the New York Times, that have “completely discredited those who said nothing improper was going on within the NSA”.

guardian.co.uk © Guardian News and Media 2013