A federal magistrate judge ordered the Trump administration on Friday to reveal the identities of the people who devised a contentious plan to create a $1.8 billion fund to compensate those who believed they were wronged by political prosecutions.

The order by the magistrate judge, Ivan D. Davis, could shed further light on how the fund was put together. The plan to create the fund, which could have funneled taxpayer money to the president’s allies, drew repeated scrutiny. It prompted a rare rebuke from Senate Republicans, and imperiled the confirmation of Todd Blanche as attorney general.

Mr. Blanche has repeatedly said the fund is dead, but President Trump has been more circumspect, indicating his support for compensating people like the rioters who were prosecuted for attacking the Capitol on Jan. 6, 2021.

Judge Davis’s order, issued in Federal District Court in Alexandria, Va., came as part of a lawsuit challenging the legality of the fund and another measure by the Justice Department that benefited Mr. Trump. That provision granted the president, his family and his businesses expansive protections against all past tax investigations.

Both the fund and the tax immunity deal emerged from backroom negotiations between Mr. Trump’s personal lawyers and senior Justice Department officials. The measures were made public after Mr. Trump agreed to dismiss a lawsuit he had filed against the Internal Revenue Service, seeking damages for claims that the agency had failed to stop the release of some of his tax returns to news organizations.

A federal judge in Florida later excoriated both the suit and the way in which it was dismissed. She said that the suit was an improper exercise in self-dealing because the president had brought claims against a federal agency that he himself controlled. She also asserted that the dismissal had been worked out with the intent to evade judicial oversight.

The suit seeking to kill the fund and the tax immunity deal was brought in Virginia by a group of plaintiffs that includes a former federal prosecutor who was fired by the Trump administration after working on Jan. 6-related cases. The group has claimed that the program was unfairly designed to help only supporters of the president.

The union representing I.R.S. workers later joined the suit, claiming that the tax provisions were illegal and could put its employees in the untenable position of carrying out unlawful orders.

Lawyers for the plaintiffs hailed the decision.

“Today’s order granting discovery is a significant step in getting to the bottom of the slush fund,” said Aman George, a lawyer for Democracy Forward, which filed the suit.

The Justice Department did not immediately comment on the ruling.