Shifting the focus from Arkansas back to the Monica Lewinsky case, Whitewater prosecutors have new momentum after a judge rejected President Clinton's efforts to use executive privilege to block certain testimony by senior aides.

Several lawyers familiar with the decision by U.S. District Judge Norma Holloway Johnson said Tuesday that the ruling means senior presidential aides, such as Bruce Lindsey and Sidney Blumenthal, must answer certain grand jury questions they previously had refused in a showdown with prosecutor Kenneth Starr.The White House could appeal, a strategy that could bring the issue of executive privilege back before the Supreme Court where Richard Nixon lost his claim a quarter century ago. Such an appeal would cause further delays in Starr's probe of an alleged presidential affair and cover-up.

Wednesday, presidential press secretary Mike McCurry said he knew nothing about the sealed ruling but dismissed the parallels to Watergate.

Meanwhile, Betty Currie, President Clinton's personal secretary and a central figure in the Lewinsky case, arrived Wednesday morning at the federal courthouse where it was expected she would give testimony for a second time to the grand jury.

One of the lawyers familiar with the ruling, all of whom spoke only on condition of anonymity, said the judge ruled that prosecutors' interest in obtaining relevant testimony in the Lewinsky matter outweighed those of the president in protecting the confidentiality of advice he receives.

The decision, filed Monday, was just the latest in a string of legal obstacles that Starr has overcome in the past two weeks.

The Whitewater independent counsel also has secured grand jury indictments against two former presidential friends, Susan McDougal and Webster Hubbell, and won a separate ruling rejecting Lewinsky's claim she had a guarantee of complete immunity from prosecution.

Still pending is a ruling from Johnson on whether Secret Service agents should have to testify about what they observed and heard from the president - an untested legal area.

After two weeks of concentrating on the Arkansas aspects of their investigation, Whitewater prosecutors Tuesday shifted their focus back to the Lewinsky case by summoning presidential friend Vernon Jordan before the Washington grand jury for a third time.