Democratic Party Chairman Howard Dean said Monday that Vice President Cheney should resign if he ordered a top aide to leak classified information to the media to defend the invasion of Iraq.

Speaking on a cable news network, Dean repeated calls he first made Sunday, saying Cheney may have broken the law if he ordered his former chief of staff, I. Lewis "Scooter" Libby, to share secret information with reporters in 2003.

"If Vice President Cheney has, in fact, ordered the leaking of political information -- of intelligence information, that means he has to step aside," Dean said. "We don't know if it's true, but he has been accused of it. If it's true, he has to step aside."

On Sunday, Democratic and Republican senators said Special Counsel Patrick Fitzgerald should investigate Cheney and others in the CIA leak probe if they authorized Libby to give secret information to reporters.

Sen. Jack Reed, D-R.I., called the leak of intelligence information "inappropriate" if it is true, and said, "I think he (Fitzgerald) has to look closely at their behavior."

Sen. George Allen, R-Va., said a full investigation is necessary. "I don't think anybody should be releasing classified information, period, whether in the Congress, executive branch or some underling in some bureaucracy," said Allen, who appeared with Reed on "FOX News Sunday."

According to a published report last week, Libby told a federal grand jury that he disclosed in July 2003 the contents of a classified National Intelligence Estimate as part of the Bush administration's defense of intelligence used to justify invading Iraq.

Fitzgerald said in the documents it was his understanding that "Mr. Libby testified that he was authorized to disclose information about the NIE to the press by his superiors."

The White House has refused to comment on the case.

Libby, 55, was indicted last year on charges that he lied to FBI agents and the grand jury about how he learned CIA operative Valerie Plame's identity and when he told reporters. He is not charged with leaking classified information.

Dean initially called for Cheney's resignation when he appeared on CBS' "Face the Nation" on Sunday. "I don't think the vice president has any credibility on national security whatsoever, and I think he's in deep trouble," Dean said on CBS.

Court documents do not identify Libby's superiors. But Dean said on Monday, "You only have one superior if you're the chief of staff and that's the vice president."

Dean said releasing classified information is "against the law ... There's a process you have to go through to declassify information. And you certainly don't release it to discredit you political opponents."