Miley Cyrus -- Big Money Offer for 'Girl-on-Girl' Porn Action

Miley Cyrus will star in a steamy NAKED makeout video with another woman -- and she might even have sex with her -- that is if she accepts a lucrative new offer from a giant porn company ... TMZ has learned.

The Media Director for Sex.com Martin Ellison just sent Miley's reps a letter, offering to compensate the singer "extremely well" for her participation in a softcore girl-on-girl make out sesh with porn star Jessie Andrews.

Martin's offer is a tit for tat, because Andrews is prominently featured in Miley's new music video "Decisions," filmed inside Beacher's Madhouse at the Roosevelt Hotel in Hollywood. (BTW the video's sick).

Martin writes, "After seeing a preview for the video 'Decisions,' we were floored at how sexy both her, and Porn star Jessie Andrews look together!" (No duh)

Miley kisses her fiance Liam Hemsworth in the video, but Martin wants to replace Liam with Jessie -- and remake the entire music video into a sexy softcore PORNO.

It's just a naked make out, but if Miley wants to make sex part of the deal, that's cool too -- Martin writes, "How far Miley chooses she wants to go is entirely up to her."

Martin says he's already reached out to Jessie's camp about the XXX remake -- and our sources tell us, Jessie's already down to clown. We're also told Sex.com will cough up $1 million.