Long John Alderton, six foot and something, the golden boy of the British television networks, has-as he puts it, slightly muddling his metaphors-placed his head on the block and taken his professional life in his hands. But the head on the block has a smile on it.s face.

It may sound overly dramatic to the layman but what Alderton has done-instead of staying home cozily counting his residuals and signing up for another couple of long run TV series-is to step boldly onto the shifting sands of international films.

He's in good company, let it be said. "Zardoz," an epic vision of the future, is the brainchild of producer - director - screenwriter John Boorman, director of "Point Blank," "Hell In The Pacific" and the memorable "Deliverance."

Alderton co - stars with Sean Connery, Charlotte Rampling and Sara Kestelman from the Royal Shakespeare Company. The 20th Century-Fox release premieres ........ at the ....... Theatre .