Jennifer Lopez isn't just saying publicly she isn't sure if she wants to return to "American Idol," she's saying it privately too ... because Steven Tyler asked her the same question and got the same answer.

We bumped into Tyler yesterday in Malibu, and in between posing for pics with a fan, he told our photog he got a big "I don't know" when he asked JLo about her plans for next season. 

And if JLo should go, Tyler didn't offer up any specific suggestions for who should take her spot ... but he did have one general qualification he feels anyone who sits in the judge's chair should meet.