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Snoop Dogg says he ALREADY DELIVERED on his promise to Le'Veon Bell -- telling TMZ Sports he laid down his track on a rap collaboration ... and it's "dope as f***."

The Steelers running back is an aspiring rapper -- and previously told us his dream was to work with the Doggfather. Snoop was down -- and told Bell to hit him up.

Good news ... Bell followed up and Snoop says they teamed up on a track for Bell's album.

Snoop also praised Bell as a pretty good rapper -- saying, "I wouldn't have did it if he wasn't good."

By the way, Snoop also says he's a HUGE fan of Damian Lillard's rap skills -- and wants to blaze a track with the NBA star too!

No word on when Bell plans to release the track -- but we're all over it.