Medical researchers today offered two new ideas that could lead to preventive treatment of a form of arthritis that affects 6.5 million Americans.

The findings -- one suggesting that a virus may trigger rheumatoid arthritis and the other linking the disease with genetic susceptibility -- were discussed at an Arthritis Foundation conference here.

"I think it is very safe to say that the Epstein-Barr virus is linked with rheumatoid arthritis," said Dr. Eng M. Tan, of the University of Colorado Medical Center in Denver. Eng and other physicians said that should their theory, which has been confirmed by two other medical groups, prove correct, it might be possible to develope a vaccine for the virus -- which also causes mononucleosis -- and put an end to rheumatoid arthritis.

It has been believed for some time tht rheumatoid arthritis develops in susceptible people when something causes their immune system to malfunction. Much research now points to a virus as a possible trigger.

The genetic link was reported today by Dr. Peter Stastny of the University of Texas Health Science Center in Dallas. "We have clearly demonstrated that the genetic marker for rheumatoid arthritis is linked to a particular chromosome and is transmitted through heredity," he said.

Eventually, he said, researchers hope to discover what other factors must be present to trigger development of the disease. The report was based on studies of 12 families, each of which had at least two members suffering from rheumatoid arthritis.