WASHINGTON — The renewed F.B.I. background check of Judge Brett M. Kavanaugh over allegations of sexual assault will be relatively limited, relying on voluntary interviews and document production.

Former prosecutors said that because it is not a criminal investigation, F.B.I. agents will not be able to get search warrants or grand jury subpoenas compelling witnesses to testify or hand over documents. Witnesses and others can refuse to cooperate, though talking to an F.B.I. agent is often a powerful motivator to tell the truth.

At a Senate hearing on Thursday, Judge Kavanaugh forcefully denied accusations of sexual misconduct. One of his accusers, Christine Blasey Ford, told senators that he drunkenly pinned her on a bed during a party on a summer night in 1982, tried to take off her bathing suit and covered her mouth to keep her from screaming.

Republicans have said for days that an additional F.B.I. background check was unnecessary but reversed course on Friday after Senator Jeff Flake, Republican of Arizona, said he would not vote to confirm Judge Kavanaugh without one. With a closely divided Senate, Republicans had little choice, and President Trump ordered the background check.