Levi Johnston's gonna have to whip out another body party -- or find some other way to make a quick $3,500 -- because a judge just ordered him to pay even more cash to his baby mama Bristol Palin.



It's kinda complicated -- but the long story short is the judge in Alaska re-crunched a few numbers and determined the $18,000 in back child support payments that Bristol had requested from Levi was way too low.

So now, according to legal papers filed this week in Alaska, Levi is on the hook for $21,561.12.

We're told that if Levi doesn't fork over the cash in a timely manner -- he could face some serious consequences ... including serious fines and possible jail time.