EXCLUSIVE

Jerry Yester -- known for playing on The Lovin' Spoonful's smash hit "Do You Believe in Magic" -- has been arrested for having child pornography ... TMZ has learned.

The Boone County Sheriff's Dept. in Arkansas tells us ... Yester was booked Thursday and faces 30 counts of possession of child porn. He was arrested by the Cyber Crimes Unit at the Attorney General's Office. He was released after posting $35k bond.