Lisa Vanderpump vs. Adrienne Maloof -- RESTAURANT WAR!

Adrienne Maloof is picking a food fight with Lisa Vanderpump by opening a competing restaurant ... and Adrienne is telling her business associates, she's gonna "kick Lisa's ass!"

TMZ has learned ... Adrienne -- who is leaving "Real Housewives of Beverly Hills" -- is opening a restaurant in Bev Hills, just blocks from Lisa's Villa Blanca.

Adrienne is telling her business partners her restaurant will blow Villa Blanca away. In fact, she's saying on a scale of 1-10 (10 being great), her archrival's restaurant gets a 2, calling it "a disaster."

As for Adrienne's eatery, it will offer comfort food -- steaks, seafood with a Mediterranean twist. It will seat 200 people and will be "celebrity friendly" -- with a private entrance in the back.

As for Lisa, she told TMZ yesterday her business is great and said if Adrienne's been complaining that "Real Housewives" hurt her business it's her own damn fault.