SAUGERTIES, N.Y. he police seldom work on a subtle but critical crime of scholarship. But a New York City detective's forensic art apparently has exposed a case of academic malprac tice. His work lends credence to theory that the Sphinx. is thousands of years older than Egyptologists and archeologists think. If it is, we must radically revise our ideas about an cient. civilization before the rise of the Egyptian culture about 3000 B.C.

Egyptologists insist that the Sphinx of Giza was built about 2500 B.C. by an Old Kingdom pharaoh, Chephren (or Khafre). But a Boston University geologist, Dr. Robert M. Schoch, ar gues that, at a minimum, a civiliza tion that preceded the pharaohs built the limestone Sphinx between 5000 and 7000 B.C. and he suggests that Chephren did further work on it.

He thinks rain caused the extensive weathering on the Sphinx. Many nearby Old Kingdom structures built from the identical limestone do not show such weathering; the inescap able conclusion is that the Sphinx was hewn earlier than they were, when the climate was far wetter.

Dr. Thomas L. Dobecki, a geophysi cist with a Houston seismic surveying company, strengthened this theory.

His analysis of sound waves that pen etrated. the subsurface limestone of the floor around the Sphinx showed that the front. and sides are twice as. weathered as the rear; this suggests the rear was carved out of the bed rock much later than the other sides.

The belief that Chephren built the Sphinx is based upon purely circum stantial evidence and unproved as sumptions. The most cherished is a fancied resemblance between the Sphinx's ravaged face and the face of Chephren perfectly preserved in a magnificent statue in the Cairo Muse um. Only Egyptologists think the Sphinx looks like Chephren; but since resemblance, like beauty, may be in eye of the beholder, revisionists felt no need to challenge the resemblance until it was "proved."

Using computer graphics, Dr. Mark Lehner, a University of Chicago Egyptologist, reconstructed the ruined face of the Sphinx as part of a three-dimensional model of the Sphinx as it appears today. He con cluded that its facial features were originally Chephren's, as traditional Egyptologists believe. But since he used the museum's Chephren as his model - it made the 3- D Sphinx "come alive," he wrote - his "proof" is a technological tautology. This cir cular logic can be used to "prove" the Sphinx was Elvis Presley.

Last fall, Detective Frank Domin go, the New York Police Depart ment's senior forensic artist, trav eled to Egypt with a Sphinx team I assembled. He carefully measured the Chephren statue and directed the photographer to get exact profile and full-face views of the Sphinx.

Despite the damage to the Sphinx's face, the statue and the Sphinx share enough undamaged reference points for Mr. Domingo to compare their facial structures. Using his police procedures, he produced an artist's impression of the Sphinx as it might have looked originally.

His report concludes: "After reviewing my various drawings, sche matics and measurements, my final conclusion concurs with my initial reaction: the two works represent two separate individuals. The propor tions in the frontal view and especial ly the angles and facial protrusion of the lateral views convinced me that. the Sphinx is not Chephren. If the ancient Egyptians were skilled tech nicians and capable of duplicating images, than these two works cannot represent the same individual."

Profound technical knowledge went into building the Sphinx and adjacent temples. If the revisionist. theory is correct, this implies that pre-Egyptian culture was more so phisticated than we ever imagined and that our ideas about social evolution and world history will need a radical overhauling.

John Anthony West, a proponent of the hypothesis that the Sphinx is older Own scholars think, is author of "The Traveler's Key to Ancient Egypt.