A judge orders the appointment of a ‘special master’ to review devices the F.B.I. seized from Giuliani.

A federal judge in Manhattan on Friday ordered the appointment of a so-called special master to review whether materials seized from Rudolph W. Giuliani’s apartment and office during an F.B.I. search in April are protected by attorney-client privilege.

The searches were part of a criminal investigation into whether Mr. Giuliani broke lobbying laws in his dealings in Ukraine before the 2020 presidential election. Mr. Giuliani was President Donald J. Trump’s personal lawyer at the time.

Mr. Giuliani was seeking to uncover damaging information on President Biden, then a leading presidential candidate. The authorities are examining whether Mr. Giuliani was also lobbying the Trump administration on behalf of Ukrainian officials who were assisting him in his dirt-digging mission, The New York Times has reported.

Mr. Giuliani has not been accused of any wrongdoing. He has said he never lobbied on behalf of the Ukrainians.

The judge, J. Paul Oetken of Federal District Court in Manhattan, said the appointment of the special master — usually a retired judge or magistrate — was “warranted here to ensure the perception of fairness.”

The special master would conduct a review to determine whether any of the material seized from Mr. Giuliani’s cellphones and computers was potentially covered by attorney-client privilege and should be made off-limits to prosecutors.

In response to the ruling, one of Mr. Giuliani’s lawyers, Robert J. Costello, said, “We knew that a special master was inevitable, which is why we did not oppose it, so this ruling comes as no surprise to us.”

The U.S. attorney’s office in Manhattan, which had sought the appointment of the special master, declined to comment.

Judge Oetken also denied Mr. Giuliani’s request for copies of the confidential government documents detailing the basis for the warrants issued in support of the searches in April, and an earlier search of Mr. Giuliani’s iCloud account. Typically, such records are only made available to defendants after they are indicted and before a trial.

Mr. Giuliani was “not entitled to a preview of the government’s evidence in an ongoing investigation before he has been charged with a crime,” the judge said.

Judge Oetken asked that the parties submit to the court proposed candidates for special master by next Friday.

Ben Protess contributed reporting.