Mayor Marion Barry and a police official said yesterday that a television news report about alleged misconduct at the District's car inspection stations was aired despite police objections that the broadcast would jeopardize an ongoing investigation of possible inspection abuses.

Barry said the investigation would continue, but that police evidence so far does not suggest any widespread misconduct on the part of city car inspectors.

The investigation was brought to light this week after a series of reports by WDVM-TV (Channel 9) reporter Mark Feldstein alleging that District taxi drivers are giving payoffs to "middlemen" who arrange to have faulty cabs pass inspection.

Barry and assistant police chief Ronal D. Cox, who heads the department's inspectional services, declined to provide further details of the city's investigation, which they said began in November 1984. But they contended that Channel 9's reports have hurt their probe.

"People have now been made aware they are under suspicion," said Cox. "People have been put on the alert."

David Pearce, WDVM's news director, said yesterday that police called the station Monday morning to try to halt the broadcast. Pearce said they refused to elaborate on the status of the investigation or to specify how Feldstein's report might harm it.

"We concluded that we had a public responsibility" to televise the report, said Pearce. He said police never asked what the report was going to say.

The mayor, Cox and Robert O.D. Thompson, administrator of transportation systems for the D.C. Department of Public Works, discussed the allegations at a news conference held at the Southwest inspection station.

Thompson said his agency told police about the possible bribery of car inspectors last November, after getting complaints about such practices from employes and citizens. Cox said police checked out some of the initial allegations and began an intensive investigation into the matter last June. "An investigation is not that quickly done," said Cox, under prompting from Barry.

The District has 40 inspectors working at its two car inspection stations. Thompson said they perform about 200,000 vehicle inspections a year, rejecting about 75,000 cars on their first inspection. Taxi cabs are inspected twice a year, and Thompson said the rejection rate is about 35 percent.

Addressing concerns that inspectors may be taking money to let unsafe cabs operate, Thompson and Barry both expressed confidence in the D.C. inspection services.

"I believe everything this government has demonstrated and can demonstrate at the appropriate time will show we have an honest system," Thompson said.

Barry, citing a case in which a car inspector was fired for alleged wrongdoing and later sued the city after a judge ordered his reinstatement, said police want to be sure before making any arrests.

"We are vigilant," Barry said. "It's easy for a camera to show one little aspect of something . . . but the police department has to present a credible case. Reporters and the media don't have the same standards about what is evidence."