Is Lisa Vanderpump QUITTING 'Real Housewives of Beverly Hills'? ... Andy Cohen to the Rescue

Lisa Vanderpump has had it with "Real Housewives of Beverly Hills" -- but executive producer Andy Cohen is fighting tooth and nail to keep her ... using Lance Bass as his secret weapon.

Sources close to production tell TMZ, Andy and Lance double teamed Lisa at her Beverly Hills restaurant PUMP over the weekend in a last ditch effort to get her to come back for the next season of RHOBH ... disguising their attack as a casual dinner date.

We're told Lisa -- who's already killing it on Bravo with her other show "Vanderpump Rules" -- has not re-upped her RHOBH contract and has told Andy she's fed up with the show ... specifically because she felt extremely bullied by the other women last season. See below.

According to sources, Cohen is extremely nervous about losing Vanderpump -- a big player on RHOBH -- and spent most of their dinner trying to convince her to stay ... it's unclear if Lisa has changed her mind. We're told Andy used Lance because he knows Lisa and Lance are good friends.