President Bush invoked executive privilege for the first time yesterday, rejecting a congressional subpoena for prosecutors' records related to a 30-year-old Boston mob case and the Clinton administration campaign finance probe.

The flexing of executive muscle outraged lawmakers of both parties, who called it an unprecedented effort to deny Congress access to records that in the past had been routinely disclosed, and launched a fresh clash between the executive and legislative branches.

But it drew approval from some GOP legal experts who lauded Bush's attempt to restore early in his tenure the notion of executive privilege, badly eroded during the Clinton administration.

Disclosure, Bush wrote in a memo instructing Attorney General John D. Ashcroft not to release the documents, would "inhibit the candor necessary" to the deliberative process in the executive branch and would be "contrary to the national interest."

"This is not a monarchy," said Rep. Dan Burton, (R-Ind.), who chairs the House Government Reform Committee, at a hearing yesterday focusing on the Boston case. "The legislative branch has oversight responsibility to make sure there is no corruption in the executive branch."

Burton hinted he might try for a floor vote authorizing the committee to sue in federal court for the documents.

His committee had subpoenaed documents regarding the FBI's handling of mob informants in Boston dating to the 1960s, specifically excluding those relating to open cases. The panel had also subpoenaed records dealing with former attorney general Janet Reno's decision not to appoint a special counsel to investigate alleged campaign finance abuses by then-Vice President Al Gore.

Burton is particularly incensed about the now-closed case of Joe Salvati, a man the FBI knew was innocent when he went to prison for 30 years on murder charges. Burton said Salvati was convicted on the basis of lies told on the stand by Joe "The Animal" Barboza, a prized FBI informant who had a grudge against Salvati.

The committee had also subpoenaed Ashcroft himself. The attorney general had been scheduled to appear on Sept. 13, but the hearing was postponed until yesterday because of the Sept. 11 terrorist attacks. Michael E. Horowitz, chief of staff for the Justice Department's criminal division, appeared in his stead.

Horowitz acknowledged Congress's oversight role and said the department has provided the panel more than 3,500 pages of documents concerning the FBI's handling of informants in Boston. What Justice has not released are "internal deliberative memoranda" that outline advice to decision-makers by line attorneys and memos that reveal confidential advice to the attorney general, Horowitz said, on the grounds that doing so "would undermine the integrity of the core executive branch decision-making function."

Joseph diGenova, a former U.S. attorney who has also served as Burton's personal attorney, praised Bush's move as one that begins to restore the principle of executive privilege after its "profligate use" by former president Bill Clinton, who asserted it at least 13 times.

"The president has done the right thing here because he is invoking the privilege early on in two historic areas of executive power: the power to conduct investigations and to keep information secret, and the decision-making process about when to initiate prosecutions," diGenova said.

But Mark Rozell, author of the 1994 book "Executive Privilege," said he thought the White House had picked poor cases for establishing the principle. A better argument would involve protecting national security, he said. "I think what the administration is doing is trying to expand the scope of executive privilege, which will serve both the governing and the political interest of the administration over the next several years, if they succeed," Rozell said.

Rozell and diGenova said Clinton had abused executive privilege by invoking it in inappropriate cases, for instance, to conceal wrongdoing or matters unrelated to the conduct of government business, such as an affair with a White House intern. But even Clinton did not assert executive privilege over the types of prosecutorial records the panel is seeking, Burton said.

Rep. Henry A. Waxman (Calif.), the panel's ranking Democrat, who has frequently clashed with Burton, yesterday agreed with his GOP colleague and called Bush's invocation of executive privilege a "reach." He put it in the context of a string of acts that he considers an abuse of executive power, including the White House's refusal to release data on its energy task force. "What we're seeing emerge from this administration is a pattern of secrecy," he said.

House Government Reform Committee Chairman Dan Burton, pointing, during a meeting on Capitol HIll angrily denounced President Bush's claim of executive privilege to Justice Department staffers Carl Thorsen, second from right, and Michael E. Horowitz.