WASHINGTON — In an extraordinary eleventh-hour action, a federal court has named an independent counsel to investigate allegations that senior White House officials were involved in efforts to obtain Bill Clinton's passport files during the presidential campaign.

The move, initiated by Atty. Gen. William P. Barr, means that Justice Department investigators found sufficient evidence of criminal action to justify the special court's appointment of an outside prosecutor.

The prosecutor's mission is to determine whether senior White House officials launched or tried to cover up State Department efforts to use government files for partisan political purposes by searching them for potentially damaging information about Clinton and his mother, Virginia Kelley.

Acting on the basis of a preliminary inquiry conducted by Justice Department lawyers, Barr asked a special three-judge court to name the counsel last Monday--one day before the expiration of a law authorizing appointment of such independent counsels, Administration sources said.

The judges picked former U.S. Atty. Joseph diGenova, now managing partner of the Washington office of Manatt, Phelps, Phillips & Kantor of Los Angeles, a congressional source said. DiGenova is a Republican who served as an aide to former Sen. Charles McC. Mathias Jr. (R-Md.) before President Ronald Reagan named him U.S. attorney for the District of Columbia. Barr and DiGenova are outspoken critics of the independent counsel statute.

Two partners in DiGenova's firm are prominent Democrats. Mickey Kantor is a close adviser to President-elect Clinton, and Charles T. Manatt is former chairman of the Democratic National Committee.

Although the specific targets of DiGenova's inquiry could not be learned, a government source said Barr decided he had to ask for appointment of an outside prosecutor because the preliminary inquiry pointed to at least one high-ranking individual. The independent counsel law requires the attorney general to seek appointment of a prosecutor when crimes are alleged involving high-level government officials listed in the act.

Earlier investigations by the State Department and General Accounting Office have focused on roles played by White House political director Janet G. Mullins, White House communications director Margaret D. Tutwiler and White House Chief of Staff James A. Baker III. All three are covered by the independent counsel act.