WASHINGTON (AP) _ The Secret Service said today it has no idea what list the Clinton White House used to improperly request 407 FBI background files on employees during the Reagan-Bush era, including some prominent Republican appointees.

Appearing before the Senate Judiciary Committee, Richard Miller of the Secret Service said the agency's lists of people with access to the White House are clearly delineated into two categories _ those who no longer have access to the White House and those who do.

Miller's testimony raised more questions about where a low-level temporary White House employee, Anthony Marceca, got a list of names for making requests for FBI background files.

The White House has embraced an explanation that Marceca was relying on an outdated Secret Service list _ but Miller said the agency updates its lists at least monthly.

``I have no idea where that list came from'' that Marceca used, testified Richard Miller, assistant director for protective operations at the Secret Service.

President Clinton's press secretary, Mike McCurry, also expressed puzzlement and said the White House has been unable to determine the origin of the list because it is not investigating the matter internally.

Of the Secret Service testimony today, he said, ``Frankly, that has left us even more confused.''

The Senate hearing occurred as Attorney General Janet Reno moved to turn over the investigation of White House requests for FBI background files to Whitewater prosecutor Kenneth Starr to avoid a conflict of interest.

Separately, three Republican senators said the Secret Service did not provide the list of names the White House used to get the files of former employees from the Reagan and Bush administrations, including some prominent Republican figures.

The White House has embraced the explanation that the FBI files were gathered by using an outdated list of Secret Service passholders.

But Sens. Christopher Bond of Missouri, Richard Shelby of Alabama and Charles Grassley of Iowa say they've been assured by the Secret Service that the agency provided no such list to the White House.

``I am appalled that this White House would risk tainting, tarnishing and staining the integrity of the Secret Service,'' Shelby told a news conference.

Bond said, ``It is clear that partisan political motivation,'' not a bureaucratic mistake as the White House maintains, ``was at the core of these requests.''

At a Senate Judiciary Committee hearing, fired White House travel office chief Billy Dale said, ``I find it difficult to believe that this was a low-level bureaucratic mistake.'' Dale said that then-White House security chief Craig Livingstone, ``in whose possession the file was kept, knew me very well.'' Dale's FBI file was obtained by the Clinton White House months after he was fired by presidential aides.

In a brief written statement, Reno said Starr agreed to accept the case if the special court which appointed him approves Reno's request.

``I have concluded it would constitute a conflict of interest for the Department of Justice itself to investigate the matter involving an interaction between the White House and the FBI, a component of the Department of Justice,'' Reno said.

Asked about Reno's move, McCurry said, ``We welcome and encourage an outside investigation.'' Of GOP critics, McCurry said, ``Hopefully, it will shut them up.''

Starr advised Reno on Tuesday that he did not believe he had jurisdiction to continue his initial inquiry into the 1993-94 background files episode.

Reno then ordered the FBI to pick up where Starr had left off and complete the investigation. But Republican presidential candidate Bob Dole and Republicans in Congress immediately questioned whether the Justice Department and the FBI could conduct an independent investigation.

As a result, Reno announced today she would ask a special three-judge court, which appointed Starr in the Whitewater case, to expand his jurisdiction.

There is no known instance of the special court denying an attorney general's request for an independent counsel to look into any matter.

The FBI investigation under FBI general counsel Howard Shapiro would presumably be turned over to Starr's investigators once the court grants the request. Shapiro had only begun planning the investigation on Wednesday.

Last week his partial investigation did not draw any conclusions about Clinton administration motives because Starr had asked him not to interview White House employees.

Examining only the FBI's conduct, Shapiro concluded that there were at least 408 unjustified requests from the White House for FBI background summaries in late 1993 and early 1994, which he called egregious invasions of privacy.

The affair has erupted into a full-scale political clash with congressional hearings underway this week before a House committee.

Congressional investigators are trying to determine whether the White House used some source of information other than a Secret Service list to generate its requests for FBI files.