In what could be a major step toward finding a treatment for muscular dystrophy, scientists reported they had discovered a gene that when defective may cause most cases of the devastating disease.

A team of British researchers said it had isolated a gene on chromosome 6 that may be the blueprint for dystrophin, a recently discovered muscle protein that is apparently defective in muscular dystrophy victims. The gene shows a strong similarity to a previously identified gene associated with one form of the disease known as Duchenne muscular dystrophy, the scientists said."This is an extremely exciting finding. If it is true, it identifies another gene that when defective can cause muscular dystrophy," said Dr. Donald Wood, research director for the Muscular Dystrophy Association in New York City.

Muscular dystrophy is a group of inherited diseases in which skeletal muscles waste away without a breakdown of nerve tissue. In all forms, there is a slow loss of strength with increasing disablity and deformity.

In 1986, researchers found the gene that causes Duchenne muscular dystrophy, the most common childhood type of muscular dystrophy that affects about one in every 3,300 boys born in the United States each year.

The remaining forms of the disease account for about 80 percent of muscular dystrophy cases in the United States, Wood said.

Since the discovery of the Duchenne gene and the subsequent identification of dystrophin, scientists have been trying to find a similar gene responsible for other types of muscular dystrophy.