In a significant setback to Queens prosecutors, a state judge dismissed a rape charge against a City Council member, saying that prosecutors had acted inappropriately during the grand jury proceedings.

The judge, Sheri Roman of state Supreme Court, said that the evidence was “legally sufficient” to support the charges against Council Member Dennis Gallagher, a Republican of Queens. And she said she would permit Queens prosecutors to convene a new grand jury to hear evidence again. The Queens district attorney, Richard Brown, said his office would do so.

But Judge Roman said that the present indictment, which accuses Mr. Gallagher of raping a woman last summer at his Queens campaign office, must be thrown out because of the types of questions prosecutors had asked Mr. Gallagher, who testified before the grand jury.

The decision offers a rare glimpse inside the grand jury room. At issue are a series of questions an assistant district attorney asked Mr. Gallagher about his marital status and his position as a City Council member.

The questions were far afield and were “an attempt to create improper inferences in the minds of the Grand Jurors,” the decision said.

At the time, the line of questioning had struck at least one grand juror as improper. The decision notes that one grand juror told the lead prosecutor, Kenneth Appelbaum, that there had been “an attempt to make (Mr. Gallagher) look foolish” by asking “disparaging questions.” The grand juror, who is not identified, had asked Mr. Appelbaum, one of several prosecutors who presented evidence, whether a judge should be consulted about the line of questioning.

At times, prosecutors had asked Mr. Gallagher about whether he continued to have sexual relations with his wife, from whom he was separated at the time. At another point, a prosecutor asked who had paid “for the carpet you had sex on?”

Judge Roman also took issue with questions about whether Mr. Gallagher had “an elevated responsibility as a role model.” Those questions, Judge Roman suggested, would seem to encourage grand jurors to treat Mr. Gallagher differently than another person in deciding whether to indict.

“The prosecutor created an unfair inference that in evaluating the defendant’s testimony and his credibility, the Grand Jury should apply a more stringent standard than the law actually imposes,” the decision states.

Judge Roman notes that her concerns mirror those of the unidentified grand juror who questioned Mr. Appelbaum about the propriety of the questions. She quotes the grand juror as asking prosecutors directly: “What does this have to do with this case?”

In a terse statement, the district attorney did not challenge any aspect of Judge Roman’s decision. Mr. Brown, himself a former judge, said “the matter will be re-presented to another Grand Jury before which the defendant can once again, if he be so advised, testify.”

It is unusual for prosecutors to take such an aggressive line of questioning before a grand jury. Unlike a verdict at trial, which requires unanimity, an indictment only requires 12 votes from a grand jury, on which 23 jurors sit.

Mr. Gallagher has said the sex, which occurred on July 8, was consensual. He met the woman that afternoon at a bar in Middle Village, Queens.

“We maintained the integrity of the grand jury proceedings were severely impaired by, among other things, the improper questioning of Councilman Gallagher,” Mr. Gallagher’s current attorney, Benjamin Brafman, told the New York Times. “Judge Roman agreed completely and to her credit and to the credit of her personal integrity and intellectual honestly, she dismissed all the charges.”

Mr. Gallagher, who is free on bail since being indicted last August, was voted out of his leadership posts by the City Council.