Kim Zolciak's coming back to 'Real Housewives of Atlanta' -- she's officially signed on to return this Fall ... TMZ has learned.

'RHOA' production sources tell us Kim will shoot for season 10, although we're told it'll be a limited role. The show wanted her back as a full-time cast member, but obligations to her other show, "Don't Be Tardy," only allowed her to sign for a part-time gig.

We're told NeNe Leakes hasn't signed on yet, though she's made it clear that IF she does return she should get more dough than Kim.

Here's the way it could work ... since Kim will only be part-time, if producers can convince NeNe to be a full-fledged cast member, they would pay her considerably more than Kim ... problem solved.