He ordered the government to turn over almost all its files to the defense, saying he no longer believed in the ability of prosecutors to make full disclosure on their own, as is customary.

Image Senator Ted Stevens of Alaska leaving court on Thursday. Credit... Jose Luis Magana/Associated Press

The surprise development came after prosecutors late Wednesday night sent to the defense team a copy of an F.B.I. report of an agent’s interview with Bill Allen, an Alaska oil services executive who is the prosecution’s chief witness and has been on the stand this week. In addition to the judicial scolding of the government, the revelation produced a heated confrontation between the chief defense lawyer, Brendan Sullivan, and the chief prosecutor, Brenda Morris, outside the presence of the jury.

Mr. Stevens is charged with failing to list on Senate disclosure forms some $250,000 in gifts and services he received from Mr. Allen and his company, the Veco Corporation, for renovations of his home in Girdwood, Alaska. The issue at the heart of the trial is whether Mr. Stevens knowingly failed to list the gifts and services. Mr. Allen has already testified that he did not send any bills to Mr. Stevens because he had been told not to by Robert Persons, his liaison to the senator.

The belatedly disclosed document is the agent’s handwritten report of an interview of Mr. Allen in which Mr. Allen said he believed that Mr. Stevens would have paid the bills had they been sent to him.

Mr. Sullivan, a well-known defense lawyer, opened the day with a theatrical protest, throwing down papers at the lectern, saying that in his 40 years of practice he had never encountered such blatant government ineptitude.