'Goonies' Sequel -- Steven Spielberg's Brainchild ... Says Richard Donner

Watch your words Corey Feldman ... 'cause "The Goonies" sequel director Richard Donner says he's working on is NOT some rogue side project -- he's working with Spielberg.

Donner tried playing mum on more sequel talk Friday while cruising Beverly Hills -- after he let the cat out of the bag earlier this month -- but the director couldn't contain himself when we asked if Steven Spielberg was also involved.

As we previously reported, Donner wants the original cast to return -- and now that he's got Spielberg behind him ... we're guessing Josh Brolin might be willing to read the script.