I'm Praying for Jim Kelly

... He'll Beat This Thing!

Jim Kelly asked for prayers -- and Kurt Warner answered the call.

The Hall of Famer tells TMZ Sports he's friends with Jim and was devastated when he heard Kelly's oral cancer had returned.

"He's a godly man," Warner said ... "He's gonna find a way through this so I'm gonna continue to pray for him."

Kurt says he's already been in touch with the Kelly family to offer a personal message -- but encourages Jim's fans to keep up the prayers because he truly believes it helps.

Jim and his wife Jill opened up about the cancer battle earlier this week. It's Jim's 3rd bout with oral cancer but this time, he says the treatment will require a major surgery that will essentially…