New York ? It was a sensational caseload that would put any prosecutor’s office on the map — or on the spot.

There was a prominent French politician accused of sexually assaulting a hotel housekeeper; two police officers charged with the on-duty rape of a young woman; and two men caught in an alleged scheme to blow up city synagogues.

But what began as a promising, headline-grabbing summer for the Manhattan district attorney’s office has been clouded by a dizzying series of setbacks inside the courthouse.

The latest setback came Friday, when prosecutors conceded the accuser in the attempted rape case against former IMF leader and potential French presidential contender Dominique Strauss-Kahn had credibility problems. The issues were serious enough that they agreed to allow a judge to lift his bail and free him from house arrest.

District Attorney Cyrus R. Vance Jr. — six weeks after he was put in the international spotlight by announcing charges against Strauss-Kahn — kept things brief when he again faced cameras outside the courthouse to deliver a prepared statement about the unfortunate turn his biggest case yet.

“As prosecutors, our duty is to do whatever is right, in every case, without fear or favor, wherever that leads,” he said. “The disclosures we made that led to today’s proceeding reflect that principle.”

Vance refused to take questions. By contrast, the accuser’s attorney, Ken Thompson, went back and forth with reporters for 20 minutes, at one point questioning Vance’s resolve.

The district attorney “is too afraid to try this case,” Thompson said. “We believe that he’s afraid that he’s going to lose this high-profile case.”

That fear, he suggested, stemmed from the stunning acquittal late last month of two police officers on charges that one had raped a drunken fashion-house staffer they had escorted home.

Jurors reached the not-guilty verdict despite dramatic testimony by the woman and security videotape showing the officers repeatedly entering and leaving her apartment building over the course of the night. They instead convicted the officers of misdemeanor official misconduct for returning to the building without telling dispatchers where they were.

Two weeks later, the district attorney’s office informed the court that, after failing to get a grand jury indictment, it was dropping the most serious charge against two defendants in a different case that had been brought with fanfare under a rarely used state terror conspiracy statute.

Police alleged the men wanted to strike a synagogue to avenge mistreatment of Muslims around the world. Federal authorities raised eyebrows by passing on the case, and the top charge was eventually dropped. The men still face lesser terrorism and hate crime charges that still could net them up to 32 years behind bars if they are convicted. But the defense has used the development to try to portray the case as trumped-up and politically motivated.

There was more bad news last week in another closely watched case — that of construction supervisors charged in the deaths of two firefighters in a high-rise blaze in 2007 near ground zero. A jury acquitted two of the defendants after their attorneys argued prosecutors made them scapegoats for the removal of a standpipe that would have provided water to fight the fire.

Meanwhile, there has been some upheaval within the office as well as in the courtroom. The chief of the sex crimes unit, Lisa Friel, told insiders this week she would leave the post she has held for nine years to seek a private-sector job — curious timing amid the high-profile Strauss-Kahn case.

She didn’t immediately return a telephone message Friday, and the district attorney’s office has declined to discuss her departure.

Both the fire and the police officers’ rape cases were launched before Vance arrived in 2010, and the terrorism and Strauss-Kahn cases have marked the biggest yet initiated on his watch.

Any misfortune probably has more to do with the risks in tackling tough cases than failings in legal tactics or internal turmoil, said Matthew Galluzzo, a criminal defense lawyer who worked in the sex crimes unit for three years until 2008.

“To say they’ve made mistakes is probably too simplistic,” Galluzzo said. “It’s more like they’ve had some bad luck and some bad publicity.”