Washington ? State and local prosecutors stretched, bent or broke rules so badly in more than 2,000 cases since 1970 that appellate judges dismissed criminal charges, reversed convictions or reduced sentences, according to the first national study of prosecutorial misconduct.

The study, “Harmful Error,” found 223 prosecutors around the nation who had been cited by judges for two or more cases of unfair conduct but only two prosecutors who had been disbarred in the past 33 years for mishandling of criminal cases. There are about 30,000 local prosecutors in 2,341 jurisdictions.

A product of three years of research by The Center for Public Integrity, a private ethics watchdog group, the study also found 28 cases involving 32 defendants in which judges concluded that misconduct by prosecutors contributed to the convictions of innocent people who were later exonerated.

Some of these innocent defendants had been convicted of murder, rape or kidnaping; some had been sentenced to death before exoneration spared them.

Charles Lewis, executive director of the center, said that by focusing only on cases in which appellate judges found misconduct the study presented “an extremely conservative and undoubtedly understated picture of the problem.” The study also excluded federal prosecutors.

Project director Steve Weinberg, a University of Missouri journalism professor on leave, said researchers found and analyzed 11,458 appellate rulings in which prosecutor misconduct was raised as an issue.

In 2,017 cases, appellate judges found misconduct serious enough to order dismissal of charges, reversal of convictions or reduction of sentences. In an additional 513 cases, at least one judge filing a separate concurring or dissenting opinion thought the misconduct warranted reversal.

In thousands more cases, judges labeled prosecutorial behavior inappropriate but characterized it as “harmless error” and allowed a conviction to stand or a trial to continue.

“We are really talking about misconduct in the cases that went to trial,” Weinberg told a news conference, noting that nationally 95 percent of defendants who are charged never go to trial.

A majority plead guilty without a trial; some charges are dropped by prosecutors.