WASHINGTON — The Justice Department will soon receive a final accounting from Robert S. Mueller III, the special counsel, of his nearly two-year investigation into how Russia influenced the 2016 election, whether the Trump campaign participated in those efforts and whether President Trump obstructed justice.

But there is no guarantee that the public will ever see that full report. The special counsel regulations say that Mr. Mueller must submit a confidential report outlining his prosecutorial decisions to the attorney general, William P. Barr, and that the attorney general must then send a summary of that work to Congress.

The regulations leave Mr. Barr considerable flexibility as to how much detail he provides to Congress and the public, discretion that was built into the regulations in response to the independent counsel Ken Starr’s decision to give Congress a lengthy — and, critics said, salacious — report on his investigation into President Bill Clinton’s sexual relationship with a young White House intern.

Once the special counsel’s office delivers its report and closes its doors, the work of the Justice Department and Congress to inform the public of Mr. Mueller’s findings begins. While Mr. Barr must tell lawmakers why the special counsel’s work concluded, he does not have a legal obligation to give them the full details of Mr. Mueller’s report.