DAMN! NAS OWES KELIS $300,000 & HE'S ALSO BEHIND ON MORTGAGE PAYMENTS ON HER HOUSE!

It's tough being a rapper trying to eke out a living with an ex-wife, a kid and an out-of-control mortgage ... but Nas may have figured out a way to stay afloat.TMZ obtained legal docs in which Nas concedes he owes Kelis a skosh less than $300,000 in spousal support. But it seems the most pressing problem is the mortgage for the home Kelis is living in -- Nas is behind $52,989.22.
So Nas' lawyer, Mark Vincent Kaplan, filed a payment plan with the court, in which the rapper agrees to pay $17,500 up front, and then pretty much double the $7,800 mortgage payment each month to catch up.

It's pretty amazing -- Kelis' lawyer, disso queen Laura Wasser, has claimed Nas raked in $244,826 a month.

According to the docs, the plan is to sell the home stat.