At one point in "Sphinx" a couple of Egyptian urchins pitch rocks at the heroine, an Egyptologist impersonated with negligible glamor by Lesley-Anne Down. Since the heroine, named Erica Baron, spends most of her screen time being pursued or intimidated by mysterious brutish assailants, these boys may have been inserted to keep her on guard during a lull in the farfetched runaround. Still, it's difficult to resist the thought that they're amateur critics who got a peek at the rushes and couldn't wait to pass judgment.

Opening day at area theaters, "Sphinx' is a melodramatic laugher that seems to combine the most synthetic devices from "The Formula" and "The Awakening." John Gielgud, ridiculous as a German scientist in "The Formula," even gets to do a funny encore in "Sphinx," garbed in caftain and white skull cap as the Egyptian merchant, Abdu Hamdi. He who puts Erica onto the previously untapped treasure of King Tut's successor, Seti I, whose gold trinkets make Tut look like a piker, before being stuffed by rival smugglers.

"Sphinx" also has an attractive dimension -- more vistas of Cairo and Luxor than "The Spy Who Loved Me" and "Death on the Nile" combined. Indeed, director Franklin J. Schaffner and cinematographer Ernest Day are obliged to emphasize stunning panoramas and sightseeing tours around the monuments rather more extensively than they might in a thriller shored up by a clever script.

The movie may have been boobytrapped from the outset by its source, a best seller by Robin Cook. The poor man's Michael Crichton, Cook is making a career out of being a doctor who can't write a lick. Ironically, Crichton helped obscure Cook's initial literary offense by streamlining "Coma" into a fairly effective movie. Schaffner and screenwriter John Byrum fail to streamline "Sphinx," which lurches and sputters from one interlude and red herring to the next.

Like the Genevieve Bujold character in "Coma," Down's character is meant to be a semi-prickly career woman whose explicit neo-feminist appeal will blend more provocatively with the traditional vulnerabilities that thrillers count on in a heroine. The assertion is built into such testy howlers as "I'm cured of men" and "Do you know what the chances are of getting ahead in Egyptology if you're a woman?" and the wonderfully wacky "I don't like being slapped even when I'm hysterical!"

The most memorable aspect of the character is her phenomenal clumsiness. The emphasis on her scholarly qualifications and devotions begin to look sheerly cosmetic when danger intrudes and she behaves like a blithering idiot.

There's also one amusingly perverse bit of business -- the discovery of an incriminating Harvard ring on the finger of a cadaver. Unfortunately, "Sphinx" would require a multitude of such playful touches to transcend its own identity as a cinematic staff.