Claudius Ptolemy, the Greek astronomer whose publication 1,800 years, ago on celestial motions brought him renown as the greatest astronomer of antiquity, has been described as a fraud.

Not just any kind of fraud either, according to a new book titled "The Crime of Claudius Ptolemy." The book's author is Robert R. Newton of the Applied Physics Laboratory at Johns Hopkins University, who says flatly: "Ptolemy is not the greatest astronomer of antiquity, but he is something still more unusual: He is the most sucessful fraud in the history of science."

If Newton is right, few of Ptolemy's observations were his own and few that were his own he either made up or made incorrectly. To hear Newton tell it, Ptolemy operated on a timeworn technique used by countless intellectual cheats. He worked backward to prove the results he wanted to get.

"I taught physics when I was younger and what poor students do to prove an experiment in physics is to make their date up," Newton said yesterday in explaining how he wrote a book suggesting Ptolemy's crime.

"It occurred to me that Ptolemy might have done the same thing my poor students used to do, so I checked into it . . . I now believe he plagiarized some ideas and made others up."

Ptolemy's astronomical work was summed up in a massive book he wrote called The Syntaxis, which, after his death in the second century A.D., became known as Almagest, which is Arabic for "The Greatest."

The Almagest was a synthesis of Greek astronomy, especially the work of Hipparchus who lived almost 200 years before Ptolemy.

The work broke down into 13 books, the first of which placed the Earth at the center of the solar system. The third book dealt with the motion of the sun and length of the year, the fourth with the moon's motion and length of the month. Later books were concerned with the motions of the planets and stars.

What Newton claims is that Ptolemy came up with his theories about the Earth, sun and moon based on measurements that Hipparchus had incorrectly made almost 200 years before. Newton says that Ptolemy claimed to have checked the measurements by Hipparchus and confirmed them when in fact he never checked them out.

"Ptolemy made no allowance for the inaccuracies in Hipparchus measurements, which he could easily have done," Newton said. "Ptolemy tells us he worked for eight years before publishing his work. The fact is he took Hipparchus' measurements on faith and never made any of his own."

Ptolemy said he observed the autumn equinox at Alexandria, Egypt, at 2 p.m. on Sept 25, 132 A.D. Backcalculations from modern tables show that an observer in Alexandria would have seen the equinox at a few minutes before 10 a.m. Sept 24, more than a day earlier.

The discrepancy is doubly strange, Newton says, because Ptolemy said he made this particular observation "with the greatest care."

Ptolemy goes on to say that he used his equinox observation to show how accurately Hipparchus had measured the length of the year. Newton says that all Ptolemy did was accept without checking the observations of Hipparchus, which were off by seven minutes.

"He wanted to be a great astronomer but he wasn't good enough to be one so he made up his data," Newton said of Ptolemy. "He's fooled people for almost 1,800 years."

Why did Ptolemy's fraud last for 1,800 years? Newton says it was because there were no competent astronomers around to point out the fraud in the 100 years after Ptolemy lived. Why not later, then?

"The next time there were competent astronomers were the Arabs of the 9th century," Newton says. "I think it didn't occur to them to check it."

Ptolemy has already found a defender in Owen Gingerich, an astonomer and historian at Harvard University. Gengerich admits that Ptolemy used "some remarkably fishy numbers," but suggests that Ptolemy used only the data that are best with his theory and did not make up data to conform with his theory.

"When Newton (Isaac, not Robert) and Einstein are considered frauds, I shall have to include Ptolemy." Gingerich says in a paper replying to a paper by Newton that preceded his book. "Meanwhile, I prefer to think of him as the greatest astronomer of antiquity."