WASHINGTON (AP) _ Two days of congressional hearings shed little light on the origin of what has become known as The List _ the document used by the White House to improperly ask for and obtain 407 FBI files on former employees.

Senate testimony by a Secret Service official Thursday failed to resolve the mystery of the FBI background files, which has become politically explosive because most of the former White House employees worked for the Reagan and Bush administrations.

Richard Miller, assistant director for protective operations at the Secret Service, said that agency keeps its list of White House passholders up to date and has no idea how the file fiasco occurred.

``I have no idea where that list came from,'' Miller told the Senate Judiciary Committee.

The White House also expressed puzzlement, with press secretary Mike McCurry saying of Miller's testimony, ``Frankly, that has left us even more confused.''

The Clinton administration had embraced an explanation that Army detailee Anthony Marceca was relying on an outdated Secret Service list when he made his request to the FBI. But Miller said the agency updates at least monthly its computerized list of 24,000 names, which clearly indicates which people still have access to the White House and which no longer do.

The lists Marceca said he relied on have not turned up.

Marceca was brought to the White House by former security chief Craig Livingstone, who was put on paid administrative leave this week because of the controversy over the files.

According to a police report provided to The Associated Press, Livingstone was investigated two years ago for threatening to ``beat in'' a neighbor's face in a dispute over a barking dog.

Adding to the White House's discomfort, Miller's statements came a day after a former White House security office employee, Nancy Gemmell, testified before a House committee that she never left behind any list of old presidential employees for her successors in the Clinton administration.

FBI general counsel Howard Shapiro, who investigated the matter and concluded last week that the background summaries were wrongly sent to the White House, testified Thursday that the FBI also was unaware of the list's origin.

Calling the episode an ``egregious'' invasion of privacy by the White House, Shapiro said the FBI also ``bears a profound responsibility for this, and we're not seeking to shirk that responsibility.'' He said the files have been kept for possible forensic examination _ which could include fingerprint analyses.

In related developments Thursday:

_Republicans moved to reinitiate contempt proceedings against White House officials in a dispute over 2,000 pages of documents relating to the dismissal of officials from the White House travel office. Rep. William Clinger, R-Pa., said he was sending a letter to the White House demanding most of the documents by next week. Should the White House decline, he said, he hoped legislation beginning contempt proceedings against White House aides could be brought to the House floor next Thursday.

The administration turned over 1,000 pages of documents last month, including material that led to the discovery of the FBI files request.

_Attorney General Janet Reno moved to turn over the FBI files investigation to Whitewater prosecutor Kenneth Starr. McCurry welcomed the independent inquiry, saying of Republican critics, ``Hopefully, it will shut them up.''

_Bob Dole, campaigning against President Clinton, used the issue as part of a swipe at Clinton for embracing conservative themes. ``I can hold up a sign for President Clinton that says, `Me, too,''' Dole said in Michigan. ``Then he can stay in Washington and read more of our FBI files.''

_Rep. Bill Archer, R-Texas, whose House Ways and Means Committee writes tax law, said he has asked the Government Reform and Oversight Committee to investigate whether the files included any private taxpayer information. ``We have reason _ good reason _ to believe there is such information in at least one of those files,'' Archer said. It is illegal for any unauthorized person to look at tax files.

_Sen. Richard Shelby, R-Ala., asked Treasury Secretary Robert Rubin if he was aware of any White House request for tax information on Bush or Reagan administration officials, or on members of Congress and their staffs. Responding, Treasury Assistant Secretary Howard Schloss said, ``there's never been such a request'' during the Clinton administration.

_On ABC's ``Nightline'' program, Sen. Orrin Hatch, R-Utah, called Livingstone and Marceca ``political henchmen'' who ought to be fired immediately. ``I certainly wouldn't have them have anything to do with the White House,'' said Hatch. Hatch said there was evidence that Livingstone and Marceca had taken items from the files and taken them from the room where the files were kept _ ``for what purpose we don't know.''