CHAMPAIGN, Ill. (AP) _ Stop, kids 3/8 Don't lift that manhole cover 3/8 You won't find Raphael or Donatello or any of the Teenage Mutant Ninja Turtles down there. They're just make-believe.

That message from Champaign school officials came as a surprise to some first graders, found peeking into a sewer in search of the fictional crime- fighters.

The result was a ''Ninja Turtle Alert'' sent last week to all elementary schools by Arlene Blank, assistant superintendent.

''Somehow, two first-grade girls managed to lift a manhole cover off,'' said Blank. ''By the time the adults got there, they had been joined by two first-grade boys.

''One of the boys was about to climb down into the manhole.''

Their motive was simple.

''They said they were looking for the Teenage Mutant Ninja Turtles,'' said Blank. ''They were very serious about it.''

Worried that other children might try the same thing, Blank issued the alert.

Her memo asks staff members to talk with pupils from pre-kindergarten through third grade and explain that the pizza-eating reptiles are not real.

Blank said the youngsters could have been injured or drowned if they had fallen into the rain-swollen sewer system.

''I think some kids think they exist,'' said Kevin Fletcher, 8. ''I don't think they're really alive. I like to think of them as make-believe.''

Originally comic book characters, the half-turtle, half-human ninja warriors are the hottest kid craze since Batman, particularly since the release of a motion picture featuring them in March.

The premise: dimestore pet turtles are dropped down a sewer manhole, fall into radioactive slime, grow to be 6 feet tall and are trained by a giant ninja rat to defend liberty.

''The Ninja Turtles are a nice story, but that's all they are,'' said Blank.