ISTANBUL — The trial is about to start in a Lower Manhattan courtroom, but it is the talk of Turkish government officials, television and even cafes.

Turkey is churning over the prosecution by the American authorities of two prominent Turks accused of conspiring to violate United States sanctions against Iran. After a failed campaign to persuade American officials to drop the case, President Recep Tayyip Erdogan last week turned to damage control, angrily denigrating the whole judicial process.

On Monday, jury selection is to begin in the Federal District Court trial amid broad speculation that the lead defendant, Reza Zarrab, who is accused of managing a billion-dollar scheme to smuggle gold for Iranian oil, has entered into a plea bargain with the prosecution and may reveal damaging evidence about corruption and illegal dealings in high places.

If Mr. Zarrab has indeed become a government witness, prosecutors are still expected to proceed to trial against a co-defendant, Mehmet Hakan Atilla, a Turkish banker who has pleaded not guilty. Seven other defendants have been charged but remain at large, prosecutors have said.