Mayor Bloomberg launched a nasty spat with two of the candidates trying to replace him at City Hall yesterday, blasting their moves to undermine his administration as “stupid” or as “intellectual dishonesty.”

Comptroller John Liu and Public Advocate Bill de Blasio were both in Bloomberg’s cross hairs — Liu for a scathing audit of the 911 system’s overhaul, and de Blasio for backing a lawsuit to overturn his outer-borough taxi plan.

Bloomberg laced into Liu during his weekly radio show, charging that the comptroller’s blistering audit of the 911 system’s costs represented “a new level of intellectual dishonesty that we haven’t even seen before.”

“This is a contract that was registered with the Comptroller’s Office, finished under the budget approved by his office, and we disallowed a lot of things,” Bloomberg said on his weekly radio show.

“Now he’s out there screaming. Maybe he didn’t even read it. It’s really hard to understand how he could say what he said . . . It’s pretty hard to answer something that’s as stupid as his charge.”

Bloomberg also got his knickers in a knot over de Blasio’s decision to join a lawsuit to block the city’s outer-borough taxi plan on the grounds it wasn’t presented to the City Council before going to Albany.

“The stupidest one is Bill de Blasio, who has sued, arguing that the law isn’t legal because there’s no local authorization,” Bloomberg said.

“The question you’ve really got to ask is why is someone like that — who is not a stupid guy — why is he opposed to getting taxi service for four boroughs that have none.”

And he questioned whether de Blasio was actually concerned about the City Council being bypassed, or was “protecting an industry rather than the people” to secure contributions for his 2013 mayoral campaign.

Records show that people affiliated with the yellow-cab industry, which opposes the outer-borough plan, have given de Blasio $76,000 since 2002, with most of the contributions made since last November.

De Blasio responded that Bloomberg should stick to the issues and keep away from the personal stuff.

“The mayor is making a bad habit of flinging personal attacks when he doesn’t get his way, but it does little good when he’s wrong on the facts,” de Blasio said.

Liu also came back punching. First his spokesman mocked the mayor’s plan to ban large-sized sodas, attributing Bloomberg’s remarks to “low blood sugar.”

A few hours later, the comptroller himself fired off an angry letter to the mayor.

“I’m disappointed by your comments on the radio, which I must say were simply offensive,” Liu wrote. “Your accusations of intellectual dishonesty are nothing more than an attempt to confuse the public and shirk responsibility on this issue.”

And if that wasn’t enough to infuriate Bloomberg, Liu added a paragraph instructing him on his duties: “As mayor, you should carefully consider the findings and recommendations of these audits.”