George Clooney's House Under Mega-Lockdown for President Obama Event

George Clooney's L.A. home is getting the Fort Knox treatment for his big Obama fundraiser tonight -- because TMZ has learned, security's so tight ... even the back-up has back-up.

Law enforcement sources tell TMZ, the U.S. Secret Service will be getting help from the LAPD as well the California Highway Patrol to keep POTUS safe at the event.

We're told the LAPD is even planning to bring in its special Counter Terrorist Unit -- Jack Bauer style.

But that's not enough for Mr. Clooney -- who we're told has taken things a step further ... hiring a special security team to oversee his own personal safety.

As for specific security measures being taken for the event -- we're told roads will be closed off, bomb-sniffing dogs will be prowling, and plain clothes officers will be on the lookout.

Oh yeah, there's also "air support" -- whatever that means.

As we reported, the party's gonna be awesome -- Wolfgang Puck himself will be catering the $40,000-a-plate affair ... and 150 bigwigs are expected to be in attendance.