WASHINGTON — The F.B.I. director, Christopher Wray, and several elite gymnasts, including Simone Biles, will testify at a Senate hearing on Wednesday on the agency’s botched handling of the Lawrence G. Nassar sexual abuse case, the first public questioning of the failure to properly investigate one of the biggest sexual abuse cases in United States history.

The hearing comes days after the F.B.I. fired one agent who initially worked on the case investigating Nassar, the former national gymnastics team doctor who ultimately was convicted on state charges of abusing scores of gymnasts, including Olympians, under the guise of physical exams.

And it comes two months after the Justice Department’s inspector general released a report that sharply criticized the F.B.I. for making crucial errors in the matter. Those errors allowed Nassar to continue treating patients for eight months at Michigan State University, where he practiced, and in and around Lansing, Mich., including at a local gymnastics center and a high school.

Nassar, who is serving what amounts to life in prison for sexual misconduct, was able to molest more than 70 girls and women while the F.B.I. failed to act, the inspector general’s report said.

Two F.B.I. agents initially assigned to the case no longer work for the agency. Michael Langeman, a supervisory special agent in the F.B.I.’s Indianapolis office, was fired in the days leading up to Wednesday’s hearing, according to two people with knowledge of the situation. Those people did not want their names published because they do not have the authority to speak about the case. The Washington Post was the first to publish news of Langeman’s firing.

Langeman, who was not immediately available for comment, was not named in the inspector general report, but his actions as the special supervisory agent, and his multiple crucial missteps, were described in detail. The report said Langeman should have known that Nassar’s abuse was probably widespread, yet he did not investigate the case with any urgency.

Langeman interviewed just one of the three elite gymnasts who gave U.S.A. Gymnastics details of Nassar’s abuse and did not properly document that interview or open an investigation. In an interview report Langeman filed with the F.B.I. 17 months after he spoke to that gymnast — the Olympic gold medalist McKayla Maroney, who was not named in the report — he included statements she did not make, according to the report.

Like other agents initially involved in the case, Langeman also did not alert local or state officials of Nassar’s alleged abuse, violating F.B.I. policy that states that crimes against children “invariably require a broad, multijurisdictional, and multidisciplinary approach.”

Langeman later said he had filed an initial report about Nassar, asking for the case to be transferred to the Lansing office because that’s where Nassar was based at Michigan State. But the paperwork wasn’t found in the F.B.I. database, the inspector general’s report said.

W. Jay Abbott, a special agent in the F.B.I.’s Indianapolis office, also is no longer with the F.B.I., after retiring in 2018. The report said he made false statements to Justice Department investigators and also “violated F.B.I. policy and exercised extremely poor judgment under federal ethics rules.” According to the report, he had been angling for a job with the United States Olympic & Paralympic Committee, and discussed it with then-president of U.S.A. Gymnastics, Steve Penny. Abbott applied for the job with the U.S.O.P.C., but didn’t get the position — yet told Justice Department investigators that he never applied.

Hundreds of girls and women who were abused by Nassar have been waiting to hear from the F.B.I. about the mistakes in the case. Biles, the Olympic gold medalist, has been vocal about wanting to know “who knew what, and when” about Nassar. She won a silver medal and a bronze medal at the Tokyo Games after dropping out of the team competition because of a mental health issue.

Biles will testify alongside former teammates Maroney, Aly Raisman and Maggie Nichols, who is known as “Athlete A” in the Nassar case because she was the first elite gymnast to report the abuse to U.S.A. Gymnastics. That was in July 2015. The Lansing office of the F.B.I. opened its official investigation into Nassar in October 2016.

Adam Goldman contributed reporting from Washington.