Brooklyn’s district attorney, Charles Hynes, who has long been dogged by allegations that he investigates his political challengers, scored a significant legal victory yesterday when a federal judge threw out a lawsuit brought by a former political foe.

The ruling came in a case filed by an attorney, Sandra Roper, who in 2001 challenged Mr. Hynes and won 37% of the vote in a primary, surprising some with her strong showing. At about the same time, Mr. Hynes’s office opened an investigation into Ms. Roper after receiving a complaint that she stole about $9,000 from a client for whom she was doing pro bono work.

An opinion released yesterday by a federal judge, William Pauley III of U.S.District Court in Manhattan, found that Ms. Roper had not convincingly shown that Mr. Hynes was personally involved in her prosecution and dismissed the case she filed against him.

“The dismissal of all the claims against D.A. Hynes affirms that his actions were appropriate,” a lawyer for the city who represents Mr. Hynes, Eamonn Foley, said in a statement sent via e-mail.

Lawyers for the city have argued that Mr. Hynes had very little to do with the prosecution of Ms. Roper, and pointed out that the district attorney’s office quickly handed over the case to a special prosecutor. In 2005, after a mistrial, a state judge dismissed all charges against Ms. Roper.

During a hearing in March, Judge Pauley pressed lawyers for the city on whether Mr. Hynes was initially responsible for the investigation.

In the decision, Judge Pauley wrote that Ms. Roper was unable to “establish DA Hynes’ personal involvement in the initiation of a criminal investigation.”

A spokesman for Mr. Hynes declined to comment yesterday.

Judge Pauley did rule that Ms. Roper could sue the administrative judge, Joan Carey, who fired her from her job as a court-appointed lawyer after she was indicted. Ms. Roper, who is black and Hispanic, claimed that other court-appointed lawyers who were not minorities have not been fired after far worse allegations surfaced.

A lawyer for Ms. Roper, Ezra Glaser, said he intended to re-file many of the same allegations in a new complaint.

Ms. Roper is one of several Brooklyn political figures who have accused Mr. Hynes in recent years of wrongfully investigating them. One of them, John Phillips, an aged former civil court judge whose name had been floated as a possible contender against Mr. Hynes, was found to be incompetent after Mr. Hynes began an investigation into whether he was the victim of a crime. Another critic of Mr. Hynes, John O’Hara, who has been tried by Mr. Hynes’ office three times for voting fraud, had encouraged both Mr. Phillips and Ms. Roper to run against Mr. Hynes.