They look pretty identical, but Rob Lowe is finally setting the record straight -- telling TMZ Sports he's NOT new Lakers GM Rob Pelinka ... but he knows what he would do if he was!

The resemblance is uncanny and people in L.A. have been talking about it ever since Pelinka got the job ... so when we saw Lowe in L.A. on Monday, we asked him if they were separated at birth. 

"How do you know I'm NOT the Lakers new GM?"

But Lowe is a big sports guy -- and says he's given real thought about what he would do if he was running the Lake Show ... even knows who he would draft.