Federal authorities on Monday charged California man David DePape with attempting to kidnap US House Speaker Nancy Pelosi last week when he broke into her San Francisco home and attacked her husband Paul.

The Justice Department said DePape had tape, rope, zip ties and other materials with him indicating he had intended to tie up Congress's top Democrat when he broke into her home on Friday, but found only her husband, whom he attacked with a hammer.

In a court affidavit the FBI said DePape told them after his arrest he viewed Nancy Pelosi as responsible for lies told by her Democratic Party.

He intended to hold the powerful House speaker -- who is second in line to the US presidency after the vice president -- hostage and talk to her, the affidavit said.

"If Nancy were to tell DePape the 'truth,' he would let her go, and if she 'lied,' he was going to break 'her kneecaps,'" the affidavit said.

DePape, 42, who lived in a garage in nearby Richmond, California and had posted right-wing conspiracy theories on social media, broke into the house early Friday when only Paul Pelosi was there.

Paul Pelosi dialled the 911 emergency number and meanwhile conversed with DePape seeking to keep the situation calm until police arrived, when DePape smashed his head with a hammer, leaving him unconscious, according to the affidavit.

Paul Pelosi, 82, underwent surgery for a skull fracture and serious injuries to his right arm and hands, and was expected to recover.

DePape later told authorities that Paul Pelosi was "taking the punishment instead" of his wife, given her absence.

DePape was charged with one count of attempted kidnapping of a US official in relation to her official duties, and one count of assault of a US official's family member in retaliation for the official's actions.

The kidnapping charge brings up to 20 years in prison and the assault charge a maximum of 30 years in prison.