WASHINGTON, April 7— Newer devices for skin tanning that emit what has been thought to be a safer type of ultraviolet radiation may be less likely to produce a bad sunburn than older machines, scientists said today, but they said cell culture tests indicate using the machines may also have adverse long-term effects.

Researchers for the Food and Drug Administration said at a seminar that studies with mouse cells show type-A radiation can cause mutations, indicating potential cancer-causing effects.

Older devices that emitted ultraviolet type-B radiation fell out of favor after reports of increased risks.