Lamar Odom's seriously considering a basketball comeback ... and his sights are set on Ice Cube's BIG3 league -- so says a man who's been tight with L.O. since college.

TMZ Sports spoke with Lamar's Rhode Island coach, Jim Harrick -- who says he just talked to Odom the other day -- and says the basketball star is pumped about the idea of joining Cube's 3-on-3 league. 

It's actually a change of heart for Odom -- who previously told Harrick he wanted to hang up his sneakers for good ... "but this 3-on-3 has got him excited!"

Coach says Odom still has a ways to go health-wise ... but "if he can get in shape, he can play with anybody." 

Odom says he's sober now -- and vows to stay clean for his family. 

LET'S DO THIS
TMZSports.com