WASHINGTON (AP) _ After decades of work, researchers think they have finally developed a monkey model for leprosy that should greatly speed the testing of preventive vaccines and treatments for the dreaded disease.

The scientists say they infected three species of monkeys with the microbacteria that causes leprosy and successfully reproduced the disease in a much shorter time than it takes to develop in humans.

In a report published Friday in the journal Science, the researchers say they found the sooty mangabey monkey to be particularly susceptible to the disease and that it may be the best primate cousin to serve as a stand-in for humans in work on the disease.

''Mangabeys may be the first reported nonhuman primate model for the study of leprosy,'' said researchers from Tulane University's Delta Regional Primate Research Center in Louisiana and the Armed Forces Institute of Pathology in Washington, D.C.

Until now, the only animal to develop the disease consistently after innoculation with Mycobacterium leprae, the leprosy organism, was the nine- banded armadillo, a creature that is physiologically far removed from man.

Leprosy, also known as Hansen's disease after the Norwegian doctor who discovered the causal bacteria in 1873, is the scourge of Biblical tales and legends that has plagued mankind for thousands of years.

The disfiguring disease, which develops over a period of years after infection, attacks body tissue, particularly skin and nerves. Untreated, the disease can lead to sores and blisters on the body and nerves so damaged that patients lose feeling in extremities, which leads to accidental injury.

Although the disease is not as contagious as once believed when sufferers were sent to leper colonies, experts estimate that there are about 4,000 active cases in the United States and up to 15 million worldwide.

Leprosy can be controlled with daily doses of drugs, but resistant strains of the organism are beginning to appear. At least two preventive vaccines are being tested, but the trials could take many years to complete because of the slow incubation of the disease and its relatively low infectivity, specialists say.

Dr. Bobby J. Gormus, principal investigator of the Tulane group, said a good primate model which rapidly and predictably develops the disease could speed testing of vaccines and new drug treatments.

''Only 5 to 6 percent of people in an endemic area will get leprosy,'' Gormus said, ''so you would have to vaccinate thousands if not millions of people before you see if it does any good years later.

''With monkeys, you can innoculate them (with the organism) and get a large percentage to develop the disease,'' he continued. ''If you give the appropriate dose, they can develop the disease in a year. So you can give them a vaccine, try to infect them, and know in a year or two if the animals are protected or not.''

Gormus said researchers have been trying to transfer leprosy to monkeys for more than a century, but with little success. While there have been a few reported cases of isolated monkeys or chimpanzees being infected, no consistent model has developed, he said.

A number of factors contributed to finding a true primate model, he said, particularly a mangabey named Louise. In 1979, the center obtained this monkey, believed to have been imported from Nigeria as an adult.

Researchers discovered she had naturally acquired leprosy, the first found in a monkey. They obtained more of these relatively scarce monkeys from the Yerkes Primate Center in Atlanta and found that they developed the disease when innoculated intravenously and under the skin with Louise's organisms, which appear virtually identical to the human variety.

Other mangabeys injected with leprosy organisms obtained from humans developed the disease, although in a milder form, the scientists reported.

Using organisms from Louise, the researchers also managed to infect some male rhesus monkeys and female African green monkeys, but were unsuccessful in attempts to transmit the disease to squirrel monkeys.

''Of the species studied, mangabeys are the most promising animal model for studies of experimental leprosy,'' they concluded.