The news for sun worshipers is not so hot.

"Catching a few rays" is getting to be a synonym for "catching cancer." And the more research there is, the stronger the connection. Skin cancer, the most prevalent form of any cancer, can be linked to sun exposure in 90 percent of the cases, according to the Skin Cancer Foundation, a national organization devoted to its control.

This year scientists have produced evidence that:

* Too much sun can cause changes in the immune systems of laboratory animals. The implication here is that the sun's rays may affect more than just the skin itself, even damaging the body's defenses against cancer and possibly other ills.

* The so-called "cool" rays of the sun, those called ultraviolet-A (UV-A), and long believed to have no harmful properties, actually may enhance the cancer-causing potential of the ultraviolet-B radiation (UV-B). The UV-Bs are the short rays you catch on the beach, especially between 10 a.m. and 4 p.m.--the kind that burn or tan. (A tan, of course, is the body's reaction to skin damage. The chemical, melanin, which gives the tan color, is secreted as a direct result of injury to the skin's pigment-producing cells.)

Specialists in skin cancer see a worldwide epidemic within the next decade. The incidence of the most serious form of skin cancer--melanoma--is up 600 percent over the last 50 years. Its incidence continues to double every 15 to 20 years. Since 1960 it has shown a greater increase in its rate of mortality than any other cancer except cancer of the lung. The death rate has doubled since the 1950s. Less deadly skin cancers--basal cell and squamous cell--match the increase not only in numbers, but in the ages of the victims.

"It is being seen," says Dr. Isaac Willis, an Atlanta-based dermatologist and skin cancer researcher "in much younger people than ever before. It is truly alarming. We're now picking up squamous cells in people in their twenties . . ."

There are 300,000 cases of these two cancers in this country every year and about 9,000 cases of the potentially lethal melanoma.

Basal and squamous cell cancers usually are not life-threatening, although the latter cancer can spread to other organs. However, either of these cancers can cause major facial deformities, sometimes because of the need for extensive facial surgery.

In addition, too-long exposure to the sun's rays, even the UV-A rays, can cause wrinkles, blotches, sagging and leathery skin as well as an assortment of other ills, including eye damage. It can worsen cold sores and other skin conditions and cause allergic reactions in those who are photosensitive or are taking medicines that sometimes endow photosensitivity as a side effect. (Some diuretics, some tetracycline antibiotics, some hypertension medications.)

"There is no such thing as a safe ultraviolet ray," says Willis.

But in addition to the voguish search for the California tan, scientists cite other factors believed to contribute to the skin cancer epidemic. These include damage to the ozone layer, which normally serves as an atmospheric sun screen, increased exposure to low-level radiation from industrial and some household mechanisms and products and some chemicals.

In response to tanning parlors' recent advertisements of "new and safe" tanning equipment, using UV-A rays, the American Academy of Dermatologists' committee on photobiology issued a warning this week.

The notion that the UV-A equipment is safer is "incorrect," say the dermatologists. There is, they report, the potential for the same kind of dangers ascribed to the UV-B equipment.

Moreover, claims that UV-A parlors can increase metabolism, efficiency of respiration, muscle performance and resistance to infection are "misleading . . . There is no scientifically acceptable evidence that UV-A radiation can promote any of these physical changes."

Some recently reported studies in Australia have also suggested that the UV-A rays emitted by fluorescent lighting may be linked to increased incidence of melanomas among those exposed to such lighting for long periods. A first attempt to replicate the study in New York was not successful, reports The Melanoma Letter, a publication of the Skin Cancer Foundation, and the matter remains in doubt pending further studies.

Dr. Willis, a keynote speaker at the Skin Cancer Foundation's First World Congress on Cancers of the Skin later this month in New York, has been reporting on the hazards of ultraviolet long-wave (UV-A) radiation for more than a decade, but confirmation of his findings has come only within the last two years. He believes that sun-screen manufacturers should be producing more products that protect against the UV-A rays as well as UV-B.

"Industry and the field of dermatology have made great strides in the field of sun-screen development," he says, "but I still feel there is room for better product development." (He concedes that no warnings will clear the beaches.)

Willis, the American Academy of Dermatologists and the Skin Cancer Foundation agree on six basic skin types ranked in order of susceptibility to sun injury and skin cancers: 1--Very fair with red or blond hair and freckles. (Always burns.) 2--Usually fair-skinned. (Tans minimally, burns easily.) 3--Light-to-medium skin. (Sometimes burns. Tans gradually.) 4--Medium-complected white. (Mimimum burning. Always tans.) 5--Darker-skinned Mediterranean type. (Seldom burns; always tans.) 6--Blacks and others with dark skins. (Never burns; tans darkly.)

Although Type 6 is less susceptible to sun injury than Type 1, no one is immune, dermatologists emphasize.

Current sun-screen preparations are graded according to the degree of protection they offer primarily against the shorter UV-B rays, numbered from the least protective (Sun Protection Factor 2 to 6) all the way to SPF-15. These stronger products may offer some protection against UV-A rays as well. The most popular ingredient in the products is Paba (para-aminobenzoic acid), which protects against UV-B rays. Ingredients like benzophenones offer UV-A protection. Watch for products offering "broad spectrum" protection.

Or, even better, try opaque zinc oxide on sensitive places (like noses and lips). Also, say the experts, loose clothing and sun hats help somewhat, as does avoiding the summer sun from 10 a.m. to 4 p.m.

Best of all--if you can--simply skip the beach.

For more information on sun screens and skin cancers send stamped, self-addressed envelopes to:

* The American Academy of Dermatology, 1567 Maple Ave. Evanston, Ill. 60201.

* The Skin Cancer Foundation, 475 Park Ave. S., New York 10016.