Sources tell us the deal has been in the works for months, and that Lindsay balked at an initial $750K offer because she wanted ... ONE MILLION dollars ... to show the world what her momma gave her (apologies for the DiLo reference).

We're told Hugh Hefner and Co. recently came back to Lindsay with an offer less than her asking price -- but close enough for her to sign on the dotted line. No word yet on which issue Linds will be featured in ... but it's a good bet she'll be on the cover.

Lindsay's rep said, "I can neither confirm or deny at this time." Playboy didn't immediately respond to our email or phone call.