WASHINGTON — Federal prosecutors rebuffed a judge’s order to release by Friday highly classified transcripts of discussions that Michael T. Flynn, the president’s former national security adviser, had with the Russian ambassador during the presidential transition.

The transcripts between Mr. Flynn and Sergey I. Kislyak, formerly Russia’s top diplomat in the United States, were expected to show that they talked in December 2016 about sanctions that the Obama administration had just imposed on Russia. Mr. Flynn initially denied those exchanges about sanctions both to Trump administration officials and the F.B.I. in the weeks after the discussions.

The conversations prompted concerns among senior Obama administration officials about whether the Trump transition team was flouting norms about holding off on making policy until after taking office. The phone calls were also at the center of the scandal that eventually prompted Mr. Flynn’s ouster just weeks into President Trump’s term.

The order last month from the judge, Emmet G. Sullivan of the Federal District Court in the District of Columbia, was unusual. The transcripts came from a secret F.B.I. wiretap of Mr. Kislyak, and their release would have provided an extraordinarily rare look at the fruits of the government’s eavesdropping. Agents routinely listen to wiretaps of foreign officials, but they remain among the government’s most closely held secrets.