A three-month investigation by the Senate's top law enforcement officer found a systematic downloading of thousands of Democratic computer files by Republican staffers over the past few years as well as serious flaws in the chamber's computer security system.

The report released yesterday by Senate Sergeant-at-Arms William H. Pickle noted that two former Senate GOP staff members -- including the Republicans' top aide on judicial nomination strategy -- were primarily responsible for accessing and leaking computer memos on Democratic plans for blocking some of President Bush's judicial nominations.

Pickle made no recommendations about whether to pursue criminal prosecutions in the case, but he cited several federal laws that might be considered, including statutes involving false statements and receipt of stolen property.

Pickle and his investigators said forensics analyses indicated that 4,670 files had been downloaded between November 2001 and spring 2003 by one of the aides -- "the majority of which appeared to be from folders belonging to Democratic staff" on the Senate Judiciary Committee. Chairman Orrin G. Hatch (R-Utah) said at least 100 of his computer files were also accessed by the GOP aides.

The report identified the two former staffers as Jason Lundell, a nominations clerk who originally accessed the files, and Manuel Miranda, a more senior staff member and later the top aide to Majority Leader Bill Frist (R-Tenn.) on judicial nominations. Miranda, the report said, advised Lundell and was said by other aides to have been implicated in leaking the documents to friendly journalists or other parties outside the Senate. Miranda had previously denied leaking the materials.

Both men left their Senate jobs during the investigation.

The report highlights a matter that exacerbated tensions on the Judiciary Committee, which was already been bitterly divided over the Democrats' tactics in blocking Bush's most conservative nominees for the federal appeals court bench.

Some Republicans on the committee -- and many conservative groups on the outside -- said the Senate should have probed the contents of the memos, which they contended demonstrated the collusion between Democrats and liberal advocacy groups, rather than how the memos ended up in Republican hands.

But Pickle's report dealt only with how the memos were accessed and leaked, not with their substance.

In addition to faulting the two aides, Pickle's report noted the "systemic flaws" in the Senate Judiciary Committee's computer security practices and recommended steps to improve them. But the report said the flaws did not contribute to the downloading and dissemination of the Democratic files by the two GOP aides.

Although some information about the incident had been reported previously, Pickle's 60-page report was the most exhaustive and authoritative summary to be issued so far.

Several Democrats called for the appointment of a special counsel to look into possible violations of federal law. "It is my view and the view of a few others that the only way to get to the bottom of this is a special counsel with full investigative powers," Sen. Charles E. Schumer (D-N.Y.) said. The Judiciary Committee plans to meet next week to decide what, if any, further steps to take.

Democrats noted that Pickle does not have subpoena powers and said further investigation is needed into whether other people were involved, including White House and Justice Department officials and judicial nominees.

In remarks before the release of the report, both at a committee meeting and a news conference, Hatch and Sen. Patrick J. Leahy (Vt.), the panel's ranking Democrat, praised the report and condemned the two aides' actions.

"Regardless of whether any criminal law was broken, the improper access was wrong and unjustifiable," Hatch said. "It will go down as a sad chapter in the Senate."

"It was wrongdoing by calculation and stealth, not by inadvertence or mistake, and we know it was intentional, repeated, longstanding and . . . systematic and malicious," Leahy said. "It was carried out surreptitiously, because those who did it knew it was wrong."

According to Pickle's report, Lundell learned how to access the files by watching a systems administrator work on his computer. Miranda guided Lundell in his accessing endeavors, the report said. In addition, the probe found "a substantial amount of circumstantial evidence implicating him," the report said.

In a statement e-mailed to reporters, Miranda said the report "fails to find any criminal hacking or credible suggestion of criminal acts," and called on Hatch to investigate the substance of the Democratic memos. He accused Pickle of having "acted improperly toward me from the first day I met with the investigators."

The probe was prompted late last year after 14 memos written by staffers working for Sens. Edward M. Kennedy (D-Mass.) and Richard J. Durbin (D-Ill.) turned up in the Wall Street Journal, the Washington Times and a conservative Web site.

The memos discussed the Democrats' nominations strategy, often in bluntly political terms, including a suggestion that action on a Michigan nominee be held up because of a pending affirmative action case.

Hatch, expressing outrage at the GOP staffers' infiltration of Democratic files, conducted an inquiry of his own and then triggered the sergeant-at-arms probe, for which Pickle used Secret Service agents and General Dynamics Corp. computer experts to trace the Democratic documents. Pickle conducted about 160 interviews and seized the hard drives and backup tapes of several Senate computers, officials said.

Sen. Orrin Hatch (R-Utah), left, and Sen. Patrick J. Leahy (D-Vt.) brief reporters on the probe of the downloading of Democratic computer files.