Three judges expressed concerns about privacy and potential abuse Tuesday as a Manhattan federal appeals court heard arguments on the legality of the government's bulk collection of phone data revealed by ex-NSA worker Edward Snowden last year.

A federal judge in New York earlier this year ruled the program was constitutional, but a judge in the District of Columbia has ruled it "almost certainly" is not. The 2nd U.S. Circuit Court of Appeals hearing Tuesday marked the first appellate consideration of the issue.

Judge Gerard Lynch complained to Justice Department lawyer Stuart Delery that despite assurances the data were used for carefully reviewed terrorism investigations, if it's "sitting there" it could be subject to Nixon-era abuses.

"We don't know what happens if some future inhabitant of the White House has a plumbers unit and decides to give them access to the data," Lynch said, referring to former President Richard Nixon's secret unit, which conducted break-ins in the name of national security.

Judge Robert Sack asked Delery how the judges could rule with confidence when the government declassified program information only after Snowden leaked documents about it.

"How do we know what you have not told us?" he asked.

The judges worried that the authority the government claims for collecting phone data to provide rapid-response ability in terror crises could be used to seize credit card and other records -- "every American's everything," Lynch said.

"Couldn't the government argue it needs to aggregate bank records to get at the same type of questions?" Judge Vernon Broderick asked.

Under the program, the government has been collecting and storing so-called "meta data" -- time, duration and dialing and receiving numbers -- for all landline and some cell numbers. The program lets the government map relationships of suspected terrorists by their calls as well as calls to and from their contacts.

The government says it does not store content and collects email under different rules.

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Delery told the judges rules on when the database can be queried about a person harmonized an effective anti-terror tool with privacy protections.

The Supreme Court has said police collection of individual phone records was not unconstitutional. Critics say storing and analyzing millions of records with sophisticated software raises new privacy issues. President Obama has proposed that phone companies store call records.

Until an alternative is in place, Sack said, he would likely stay any ruling striking down the program, so as to give Congress and the Supreme Court time to react.

"Suppose we're wrong," he said, "and someone blows up a subway train?"