Dr. Jonas E. Salk, who made medical history by developing the polio vaccine, has been given the go-ahead by the Food and Drug Administration to test on humans his new drug which he thinks might arrest multiple sclerosis.

FDA approval, according to a spokesman, means the agency believes there is enough evidence that the drug might work, that it is "worthy of clinical testing and the plan set forth is adequate."

MS is a chronic and crippling disease of the central nervous system. It is estimated that one in 20,000 Americans suffer and eventually die from it. Eli Lilly Research Laboratories, which is preparing the experimental substance for Salk, cautioned that research is at an early stage and may not meet with success.

In a prepared statement from his La Jolla, Calif., institute, Salk said there is no known cure for MS. But for many years he has been studying an animal disease, called allergic encephalomyetitis, the pathology of which he said is similar to MS. The tests on MS patients, he said, "will determine whether it is due to a similar allergic reaction."

A spokeswoman for Salk said the animal tests were used to develop a model for a drug to combat MS, "and have gone as far as they can go without testing in humans." She said the tests will be conducted on a "handful" of patients in the San Diego area, who will work with clinical neurologists there.

The substance under study is called myelin basic protein and is extracted from a pig's nervous system. Dr. Irving Johnson, a cell biologist and research vice president for Eli Lilly in Indianapolis, who will monitor the experiments, said that an MS patient "mounts an immunological attack against his own nervous tissue," thus causing a slow, debilitating deterioration of his condition over many years until he dies of infection.

By injecting myelin basic protein, Johnson said, experimenters hope to "block that attack, which is a patient's response against his own tissue, and stop the progression of the disease." But he said it would be unlikely the drug could repair damage already done.

He said one trail of injecting MS patients with myelin basic protein was conducted several years ago on 20 to 40 patients. He said there was "no clear clinical improvement, but it didn't make their condition any worse."

A Lilly spokesman said Salk developed the substance and then asked Lilly to "refine it and produce it in a form suitable for preliminary animal studies." Lilly is now making the injection for human testing.

"The agent Salk and Lilly have been working with has been effective in treating this condition in animals," the spokesman said. "But we have no idea if it will be useful in humans suffering from MS . . . A lot of things react one way in animals and another way in humans, and it could be many years before we know."

Salk added that "it will be several years before conclusions can be drawn as to its significance in clarifying the cause of MS."

An FDA official said the FDA approved Salk's "investigatory new drug application," as it is called, early in December and expects testing to begin this month. Approval, he said, meant reviewing the application, looking at the animal studies and making sure of the method and safety of the research plan.

"Our purpose in giving approval," the official said, "is protecting patients and letting them know there is potential risk they should understand before giving their informed consent."