Paul Petrides, one of the leading Paris art dealers and considered the top expert on postimpressionist paitner Maurice Utrillo, was sentenced yesterday to three years in prison and fined more than $500,000 for selling a stolen art collection.

Petrides, who is 78, probably will not actually have to serve the prison term because of his advanced age, but the conviction was a major victory in a drive here to hamper the work of art-theft rings.

The prosecution, conducted in a Paris court by Jean-louis Guyot, stressed its view that international art theft is second only to the drug trade in international crime and that without legitimate art experts like Petrides willing to lend their reputaions as covers, crime syndicates could not work on the present scale in the art world.

Guyot painted a picture of Petrides as "one of the greatest art predators" who had preyed on artists throughout his career, reaching an early peak in his exclusivity contract with a declining and alcoholic Maurice Utrillo in the 1930s, providing the desperate painter with a bottle of red wine for each painting that he delivered.

For Petrides, it was literally rags to riches. He came to Paris in 1920 as an illiterate tailor from his native Cyprus. He entered the art world by marrying a dealer and met promising artists through her, including Van-Dongen, Vlaminck and Foujita. He opened his first gallery in 1935. He shrewdly swapped suits for paintings.

After the Nazi occupation of Paris in 1940, Petrides was one of the few gallery owners to remain open. One of the main items in the local art trade was works seized from absent or deported Jewish collectors.

There have recently been allegations emanating from Israel that Petrides was involved in that trade. In any case, he was one of the few British subjects allowed to remain active in occupied Paris, and the difficulties were overcome altogether for him when Hitler's French puppet, Marshal Philippe Petain, made Petrides a naturalized French citizen in 1943.

Petrides managed to short-circuit accusations of collaboration with the Germans, pointing out that he had provided paintings for a gallery that served as a cover for the top Free French representative inside France. In 1960, the former tailor opened his present gallery in the Rue de la Boetie in the Right Bank neighborhood of fashionable, high-priced art galleries.

What tripped Petrides up in court was the numerous contradictions and professions of naivete in his testimony over the resale, in large part to Japanese collectors, of more than half of the 31 stolen Renoirs, Corots and Utrillos taken in 1972 from the home of Albert Lespinasse, president of BANANIA, the French answer to Ovaltine.

Manifests prepared for French customs by Petrides' gallery systematically misrepresented the sizes, subject-matters and painters of the works shipped abroad to a country with which France has no extradition treaty.

Petrides blames all that on an inefficient secretary and insists that he had no idea that the canvases were stolen, even though a large number were presented to him without frames and some of them were cut off their wooden stretchers with razors.

Petrides' books showed that he paid a fraction of the paintings' worth. A police inspector friendly with Petrides for more than 30 years testified that this did not arouse his suspicious in the early part of the investigation because it struck him simply as a "very French" effort to avoid taxes.

Not content to explore the circumstances of the resale, prosecutor Guyot set out to destroy Petrides' reputation as Utrillo's protector and promotor. Petrides, said Guyot, "knew how to make Utrillos with red table wine just like, later, others would make chickens with hormones. . .What will give value to a Utrillo in the future will be not to have passed through the hands of Paul Petrides, fence and smuggler."

Guyot spoke of the "deplorable splotchings" that the painter of melancholy Paris street scenes produced under the alcohol-induced influence of Petrides.

Guyot rounded on a whole class of "lamentable" art experts "who don't have archives but claim to have an eye."

"The underworld," Guyot said , "would not be so interested in works of art if it did not have the certainty of being able to sell them and thus to have guarantees from certain of those who hold the monopoly of the authentication and the sale of those works. The Petrides affair demonstrates the correctness of that hypothesis."

The judge - on hearing during the trial of a certificate of authenticity issued by the daughter of the painter Rouault and her subsequent retitling of the painting by her father without bothering to inquire where it came from - mused, "It makes ine wonder about the mores in the world of art."

The French interior ministry issued statistics last month showing a rise of nearly 20 percent in art thefts last year in France, notably from private collections like Lespinasse's. In that job, the thieves coolly bound and gagged seven persons, including Lespinasse, while they worked for more than three hours at removing the paintings and all the documents relating to them.

According to the ministry, 42,000 works of art valued at more than $30 million are stolen annually.