WASHINGTON — A highly anticipated Justice Department inspector general’s report on aspects of the Russia investigation, including its origins and whether the F.B.I. abused its surveillance powers, will be released early next month, according to a letter released on Thursday.

The inspector general, Michael E. Horowitz, plans to release the findings of his investigation on Dec. 9, “barring unforeseen circumstances,” he wrote in a letter to Senator Lindsey Graham, Republican of South Carolina and the chairman of the Senate Judiciary Committee.

The report will bring to a close a nearly two-year inquiry into how law enforcement officials opened their investigation in 2016 into Russia’s election interference and whether anyone associated with the Trump campaign conspired. Among the focuses of Mr. Horowitz’s inquiry are how investigators obtained a secret warrant to wiretap a Trump campaign adviser, Carter Page, including the still-unclear extent of their reliance on research compiled into a now-notorious dossier by a retired British intelligence official, Christopher Steele, whose work was funded by Democrats.

The special counsel, Robert S. Mueller III, eventually took over the inquiry. He affirmed the intelligence community’s findings that Russia conducted a widespread, coordinated effort to interfere in the election, but he found insufficient evidence to charge any Trump associates with conspiring with the Russian operation to sway the election. He declined to say whether President Trump obstructed the investigation itself.