House Government Reform Committee Chairman Dan Burton on Wednesday renewed his criticism of the Bush administration for refusing to turn over documents about the FBI's handling of Boston mob informants in the 1960s.

Burton, R-Ind., is trying to build a case that previous administrations have regularly turned over the kinds of prosecutorial documents that Bush ordered Attorney General John Ashcroft to withhold from the committee in December, citing "executive privilege."

"If we can't see the Boston documents, then isn't it fair for us to conclude ... that Congress will never get deliberative documents from the Justice Department? Unfortunately, I'm beginning to come to that conclusion," he said at the start of a hearing at which a Justice Department attorney was to explain the reason for withholding the material.

Burton has amassed a list of instances where Congress has accessed such documents, dating back to the anticommunist Palmer raids and Teapot Dome scandal of the early 1920s. Among those scheduled to testify Wednesday were Mark Rozell, a political science professor at Catholic University who has written a book on executive privilege.

California Rep. Henry Waxman, the ranking Democrat on the committee, said the Bush administration has used executive privilege to block access to documents on issues such as the census.

"There can be no accountability when the government chooses to operate in secrecy," he said.

Executive privilege is a doctrine recognized by the courts that ensures presidents can get candid advice in private without fear it will become public.

The Constitution doesn't mention it; its meaning has been defined over the years by presidents, judges and government policies. But since George Washington, presidents have used a form of privilege to keep information from Congress or the courts.

Bush argued that he was worried about chilling prosecutors' private deliberations in criminal cases in invoking privilege in the Boston mob case and the Clinton-era fund-raising investigation of the 1990s. Wednesday's hearing is focused only on the Boston case.

Angry lawmakers accused Bush of trying to create an "imperial presidency" by thwarting Congress' ability to oversee the executive branch. Burton, who subpoenaed the records, threatened to take him to court.

The case is emblematic of the struggle between the White House and Congress over how much information the administration is willing to share with lawmakers.

Senators recently complained that Bush didn't consult them before deciding some terrorism defendants could be tried by secret military tribunals.

Other lawmakers have been frustrated by their inability to get information about the administration's deliberation on a national energy policy, and Congress' investigatory arm is considering suing the White House over energy meeting records.

The Boston case stems from revelations that Joseph Salvati of Boston spent 30 years in prison for a murder he did not commit even though the FBI had evidence of his innocence.

Salvati's conviction was overturned in January after a judge concluded that FBI agents hid testimony that would have cleared Salvati because they wanted to protect an informant. Salvati had been paroled in 1997.