When KIM CATTRALL big-mouthed prematurely that a big-screen “Sex and the City” sequel’s already gearing up, her shocker triggered an instant angry reaction from star SARAH JESSICA PARKER – because real hardball’s happening behind the scenes.

Even though Sarah Jessica, CYNTHIA NIXON, KRISTIN DAVIS and Cattrall are all anxious to sign on and savor another star trip, producers are warning the “Sex” kittens NOT to make any outrageous salary demands – even threatening to ruthlessly write out and recast anyone who holds out for “unreasonable” buck$$!

Here’s the kicker: Four young hotties will be written into the story line to freshen the franchise when the current quartet goes geriatric.