Mr. Steele’s dossier claimed that Russian intelligence officers had used blackmail and bribery to try to turn Mr. Trump into a source, and Mr. Horowitz’s investigators examined whether law enforcement officials improperly relied on it to seek a wiretap for the former Trump campaign adviser, Carter Page, who visited Russia during the campaign.

Mr. Steele has made clear to associates that he considered the dossier to be a starting point for further investigation, not established facts. It has grown clear in the years since Mr. Steele compiled his dossier that while many Trump aides welcomed contacts with Russians, some of its most sensational claims appeared to be false or were impossible to prove.

The more than 400-page inspector general’s report is expected to debunk the idea that the F.B.I. relied on the Steele dossier to open its Russia investigation, though it was used to apply for the warrant to wiretap Mr. Page. It is not clear the extent to which the application for the warrant relied on the dossier.

Mr. Trump’s allies have emphasized that Mr. Steele compiled the information for a research firm, and that the firm was paid by lawyers who worked for Hillary Clinton’s campaign and the Democratic National Committee. They have argued that it was inappropriate to use partisan opposition research in a sensitive application to wiretap a person associated with a presidential campaign.

The inspector general is expected to say that the Justice Department did not know the identity of Mr. Steele’s patrons when they used some of his information in the original October 2016 application to wiretap Mr. Page. But he will be critical about the fact that law enforcement officials did not change the language about who paid for the research in later wiretap renewal applications, after officials learned that Democrats had funded the research, according to people familiar with a draft of the report.

Mr. Horowitz will also fault the F.B.I. for not telling the judges who approved the wiretap applications about potential flaws with the dossier.

He is also expected to criticize contact that Mr. Steele had with Bruce G. Ohr, a Justice Department official and Russian organized crime expert who shared information from Mr. Steele with the F.B.I. even after the bureau ended its relationship with him as an informant in the fall of 2016.