Lindsay Lohan: I Didn't Want to Fire Shawn Holley ... BUT

Lindsay Lohan is telling friends ... she never authorized her New York lawyer to fire Shawn Holley and never instructed him to send her a letter of termination ... but there's one BIG problem with her story.

Sources connected with attorney Mark Heller tell TMZ ... Lindsay SIGNED the letter he sent to Holley earlier today, giving her the boot.

TMZ broke the story ... Holley was 86'd just before a scheduled meeting with the judge and prosecutor in Lindsay's lying-to-cops case, trying to plea bargain it away.

Lindsay is now telling friends ... she desperately wants Shawn back on board. She's saying she thinks of Shawn as a second mother -- interesting, considering she barely has a first.

Lindsay says she knows Shawn is an ace in court and she would never drop her the day before she's scheduled to go to court. As you know, the judge set a hearing tomorrow to decide if Lindsay violated her probation in the jewelry heist case by allegedly lying to cops in the car accident case. Again ... Lindsay signed that letter.

As for whether Shawn will take her back ...