WASHINGTON -- The U.S. Supreme Court wrestled yesterday with the claim that public employees punished for their on-the-job speech can use the First Amendment to sue their bosses, a broader protection for whistleblowers that several justices warned would undermine efficient government.

"The intrusive consequence of your rule is sweeping," Justice Anthony M. Kennedy told Bonnie I. Robin-Vergeer, the lawyer for Richard Ceballos, a Los Angeles deputy district attorney who said he was demoted for writing a memo to his superiors questioning the validity of a search warrant.

"Are federal courts going to supervise the everyday dialogue that goes on in every agency?" Justice Kennedy asked.

But other justices groped for a middle ground that would allow a fired or demoted public employee to sue his employers by citing the First Amendment if his inside-the-office speech were related to an important constitutional principle, like the right to a fair trial.

"What if a lawyer thinks he has an ethical obligation to disclose [police wrongdoing]?" Justice David H. Souter asked Cindy S. Lee, the lawyer for the district attorney's office. "Is there no First Amendment protection?"

After warning his superiors that a deputy sheriff may have lied in an affidavit supporting a search warrant, Mr. Ceballos informed the defense attorney in the case that the affidavit contained falsehoods and later testified about the document at a court hearing. He said his superiors retaliated by demoting him and transferring him to a remote assignment.

The 9th U.S. Circuit Court of Appeals in San Francisco refused to dismiss Mr. Ceballos' suit, citing a 1968 decision in which the Supreme Court said a school district violated a teacher's First Amendment rights when it fired him for writing a letter to a local newspaper criticizing the school board.

In that and later cases, the high court said a public employee is protected by the First Amendment when he speaks out as a citizen about a "matter of public concern." But courts must balance that right against the possible disruption their speech would cause in the workplace.

The 9th Circuit said Mr. Ceballos was entitled to First Amendment protection even though he expressed his opinion in an internal memo because his motive was to call public attention to possible wrongdoing, not just to further his career.

But Ms. Lee told the justices that on-the-job speech by government employees "should not be protected by the First Amendment. There is no need to go into balancing." She was supported by Dan Himmelfarb of the U.S. Solicitor General's Office, representing the Bush administration.

Justices Kennedy and Antonin Scalia and Chief Justice John G. Roberts Jr. seemed sympathetic to the position of the district attorney's office.

In a serious exchange with a humorous punch-line, Chief Justice Roberts asked Ms. Robin-Vergeer why he shouldn't be able to fire a law clerk who disobeyed his instructions and repeatedly wrote memos referring to the "wacky" legal philosophy of another member of the court.

"Nobody's wacky here!" interjected Justice Scalia.

Justices Souter, Ruth Bader Ginsburg and John Paul Stevens expressed more sympathy for Mr. Ceballos' position. Justice Souter noted that the 9th Circuit, which has jurisdiction over several Western states, had first ruled in 1988 that the First Amendment applied to cases like Mr. Ceballos', and yet there had not been a "deluge" of lawsuits by public employees in those states.

Two justices indicated that the case could be resolved without establishing a new rule that might flood the courts with suits by public employees.

Justice Sandra Day O'Connor suggested that Mr. Ceballos' lawsuit might be disposed of under a "proper application" of the 1968 ruling allowing courts to weigh a public employee's free-speech rights against the disruption a lawsuit might cause.

Justice Stephen Breyer, looking for "middle ground," pressed Ms. Robin-Vergeer to identify a category of protected workplace speech that was narrower than speech about "a matter of public concern." He said: "Our law clerks meet [that standard] every day."