Attorney Mark Geragos says the new Los Angeles County District Attorney has no clue what he’s talking about when it comes to the Menendez brothers … telling us Nathan Hochman needs to brush up on the facts.

Mark, who is repping Erik and Lyle as they seek to get out from prison after three decades behind bars, joined us on “TMZ Live” Monday and offered a scathing reaction to Hochman’s latest press conference.

For Mark, the whole thing was ridiculous and irrelevant … and not just because Hochman was talking about a resentencing hearing that no longer holds weight due to California Governor Gavin Newsom circumventing the process.

Hochman went on and on for more than 45 minutes before even taking a question … and Geragos says the county’s top prosecutor didn’t make a whole lot of sense, and didn’t seem to understand the case or the laws surrounding resentencing.

Newsom already made the upcoming resentencing hearing moot when he ordered a risk assessment for the Menendez brothers … because if the judge approved resentencing, the case would go to the parole board, and they already have the case at Newsom’s behest. So, Hochman was just grandstanding here.

Geragos says Hochman may have used the platform to set up a potential run for Governor … and tells us how he’s allegedly violating the law.