District Attorney Terence Hallinan said he plans to review the prosecution of Police Chief Earl Sanders and six police supervisors and could decide to drop the case.

Hallinan said in an interview Friday there is "no question" that the upper echelon of the Police Department tried to impede the investigation of three off-duty officers who were involved in a brawl in November, but there may not be enough evidence for a criminal conviction.

"The issue is: Is there a conspiracy? Can I find enough evidence?" he said. "If I can't prove the case, if I don't believe I can prove it, then it is my obligation not to follow through with it."

Hallinan said he would read the grand jury's transcripts and would have a better idea this week of whether to proceed with conspiracy charges against the chief and six commanders. He also said he is considering possible alternatives to prosecution, which he declined to identify.

The statements marked the first time that Hallinan has publicly acknowledged that he might not proceed with the controversial case. He had faced criticism in recent days from legal experts who questioned his allowing the grand jury to return conspiracy indictments against the police commanders.

Published reports earlier Friday revealed that, before the grand jury returned indictments against the chief and supervisors Feb. 27, the D.A. had told the panel there was not enough evidence to indict them.

Hallinan called a news conference Monday and insisted that his office would go ahead with the prosecutions, dismissing allegations by critics that he let the grand jury get out of control and saying the release of grand jury transcripts would answer any doubts about the charges. "These specific allegations of assaults by off-duty police officers and a subsequent coverup by high-ranking police command officers are extremely distressing," Hallinan said at the time.

"They strike at the heart of our civil liberties."

But by Friday, Hallinan sounded considerably more equivocal.

He said he believed he was required to file the indictments after the grand jury handed them down, but that he legally must ask for them to be dismissed if he believes the evidence is not there to convict.

Hallinan is running for reelection in November. Asked whether it might hurt him politically to drop the case now, he said: "I really can't worry about the politics of it right now."

Other political observers said Hallinan's case against the police officials has support among the city's liberals, Hallinan's base of political support. But they said he could suffer significantly at the polls if he fails to win a single conviction or if the case is thrown out by a judge before trial.

To prove a conspiracy to obstruct justice, legal experts said, Hallinan would have to show criminal intent. The evidence would have to show there was an agreement among the Police Department's management to obstruct the investigation, legal experts said.

University of Santa Clara law professor Gerald Uelmen said the charge could be proven with evidence of one act by one individual, such as destruction of records, as long as it was done while all the individuals were members of the conspiracy.

Criminal defense lawyer Cristina Arguedas said conspiracy is difficult to prove. "It would be very unusual to prove those charges if you didn't have either an undercover tape recording or a wiretap or an informant," she said.

Other legal experts said Hallinan also might be able to prove his case if he struck a deal with one of the indicted officers to testify against the others. So far, though, the officers have appeared united.

Laurie Levenson, a professor at Loyola Marymount Law School, said Hallinan's comments indicate that he is feeling the heat of public pressure. "It sounds like he's been reading the papers," she said.

But Levenson said Hallinan would be wise to reconsider before the case goes to trial. "The way I see it, it's better late than never [to call off the prosecution]. It's the right approach to take now," she said.

Levenson and others said there may have been a level of poor police conduct that did not cross over into illegal behavior.

"There is a line between maybe unprofessional police work and criminal obstruction conduct, especially a conspiracy," Levenson said.

"Just because officers were unsupportive of the investigation, that in itself doesn't translate into conspiracy."

San Francisco Assistant Police Chief Alex Fagan, left, and Police Chief Earl Sanders, center, shown at a March 4 arraignment with Police Officers Union head Chris Connie, are accused with five others of trying to cover up an off-duty brawl.