The Justice Department’s inspector general found no evidence that the F.B.I. attempted to place undercover agents or informants inside Donald J. Trump’s campaign in 2016 as agents investigated whether his associates conspired with Russia’s election interference operation, people familiar with a draft of the inspector general’s report said.

The determination by the inspector general, Michael E. Horowitz, is expected to be a key finding in his highly anticipated report due out on Dec. 9 examining aspects of the Russia investigation. The finding also contradicts some of the most inflammatory accusations hurled by Mr. Trump and his supporters, who alleged not only that F.B.I. officials spied on the Trump campaign but also at one point that former President Barack Obama had ordered Mr. Trump’s phones tapped. The startling accusation generated headlines but Mr. Trump never backed it up.

The finding is one of several by Mr. Horowitz that undercuts conservatives’ claims that the F.B.I. acted improperly in investigating several Trump associates starting in 2016. He also found that F.B.I. leaders did not take politically motivated actions in pursuing a secret wiretap on a former Trump campaign adviser, Carter Page — eavesdropping that Mr. Trump’s allies have long decried as politically motivated.