A senior Justice Department official said yesterday that the Reagan administration ought to have broad authority to hire, fire and control the investigations of independent counsels appointed under the Ethics in Government Act.

Assistant Attorney General John R. Bolton told a Senate subcommitee that he regards the 1978 law governing the appointments as "unconstitutional" in every important respect and suggested that it be changed to win the Reagan administration's support for renewal. It is due to expire in January.

Sen. Carl Levin (D-Mich.), chairman of the Governmental Affairs subcommittee that oversees the law, accused Bolton of proposing what amounted to a return to the "very dark days" of Watergate, when President Richard M. Nixon fired special prosecutor Archibald Cox for insisting on access to Nixon's White House tapes.

At the witness table for almost two hours, Bolton said the Justice Department has "very grave doubts about the constitutionality of the appointment process" in the law, whereby independent counsels are chosen by a special three-judge federal court.

Bolton did not offer any specific proposals to replace the current law, but he said in his prepared testimony that the department is working on draft legislation that would be, in its view, both "constitutionally sufficient and capable of ensuring public integrity."

He said the attorney general should have the power to appoint independent counsels but that, "once appointed, the independent counsel would operate independent of the attorney general pursuant to appropriate regulation."

In general, however, Bolton said that "under the constitutional system of separation of powers, the president or his delegate, must retain the unfettered ability to direct and supervise all executive officials . . . . Any statutory restriction on presidential removal of a federal prosecutor like the independent counsel must yield to the explicit constitutional responsibility of the president to direct the prosecutor's execution of the laws."

Asked about the views of Attorney General Edwin Meese III, Bolton replied, "the attorney general quite properly reserves judgment." The Justice Department has avoided taking a clear position on pending challenges to the appointments of independent counsels Lawrence E. Walsh in the Iran-contra affair and Whitney North Seymour in the case against former White House deputy chief of staff Michael K. Deaver.

Bolton maintained that practical politics would prevent a recurrence of the 1973 "Saturday Night massacre," so called because Nixon had to fire his attorney general and his deputy attorney general before finding someone at Justice who was willing to fire Cox.

"You're saying, 'just forget all that,' " Levin charged in angry tones. "You're asking for something that's a nonstarter around here."

Bolton responded that "any president would pay an enormous price" for firing an independent counsel in the midst of an investigation and that this would be a sufficient check on its happening again. "It happened only once before, and we can ask Richard Nixon what price he paid for it," Bolton told the subcommittee.

Testifying as chairman of Common Cause, the self-styled Citizens' lobby, Cox added "a personal note," asking the subcommittee to consider the case of a president who ordered an independent counsel not to challenge the president's claim of executive privilege or not to insist on subpoenaing the president's records.

"You know that can happen because it did happen, in just about the terms I've stated," Cox said.

Levin also accused the Justice Department of systematically undermining the 1978 ethics law by refusing to conduct preliminary investigations when the statute requires it, showing insensitivity to conflicts of interest on Meese's part, making judgments that should be made only by the independent counsels and opposing one prosecutor's request to broaden her investigation to cover a college classmate of Meese's, former deputy attorney general Edward Schmults.

Bolton defended the actions of the department and Meese, denying any effort to "derail the process."