Take a deep breath and close your eyes and this minimal, second rate intrigue goes down even if it is hard to swallow. Most of it takes place underwater when Mike Brooks Is sent to Durban, S.A., to release a missile from a nuclear- powered Russian submarine. In spite of sharks, and in spite of two Russian heavies, and one who is considerably, more lissome, Deirdre with a ""delectable, curvaceous form,"" he makes it after a savage fight on the ocean floor. Up and over--blup, blup, blup, blup. Just like Sea Hunt.