You're really proud of your tan. All summer long you've basted and baked, slathered in greasy gunk. And now, as the sun heads for the equator and summer heads for the photo album, you're on your way to the beach for one last lost weekend of soaking up the rays.

But wait! Do you really want to do it? The more reason you have to be proud of that tan the more reason you have to worry that you may become a cancer statistic, or at least that you may get saggy, wrinkly, skin that's old before your time.

Tanning in the normal course of summer events is fine, say the experts, but making a fetish of tanning is not, particularly if you're a blond or a redhead or have blue eyes.

According to Dr. John Potter, director of Georgetown University's Vincent T. Lombardi Cancer Research Center, blonds, redheads and people with blue eyes account for 80 percent of the victims of skins cancer. And there is very definitely a correlation between excessive exposure to the sun and disease, he says.

It is no mere coincidence that the greatest incidence of the three major types of skin cancer occurs in the South and the area known, for obvious reasons, as the Sun Belt, says Potter. "There's no doubt about the general fact that excessive exposure to sunlight will increase the chances of skin cancer," he said.

The least worrisome of the three types is called basal cell skin cancer. "It's a type of cancer that arises in the skin in the basal cells. It's an indolent form of cancer. It grows very slowly," Potter explains. "If it's treated properly you can almost guarantee a complete cure."

The next form of the disease is squamos cell skin cancer. "This is a little bit more aggressive, but most of the time . . . it can also be managed very successfully by appropriate measures," which may include surgery and radiation therapy.

Both basal cell and squamos cell cancers usually appear as small, open sores that refuses to heal, says Potter. As is the case with any other sore that does not appear to be healing properly, the person with such a problem should seek immediate medical attention.

The third, and most serious, form of skin cancer is melanoma. "Usually a pigmented tumor, it's usually a bluish-blackish color. It can . . . spread to the rest of the body. This type of cancer is definitely a significant form of cancer," says Potter, who adds that most melanomas will "arise in a pre-existing mole, although not all moles can turn into a melanoma." Even with treatment, victims of this form of cancer have only about a 50 percent five-year survival rate.

Although there are only six to eight new cases of skin cancer each year for every 100,000 persons, Potter points out that those with fair skin, and particularly blue eyes, are far more susceptible and therefore should be much more careful about exposing themselves to the sun.

"I can see no advantage to prolonged sunbathing and sunbaking," he says. "I think you can develop a tan and should in the summer time, but you can only tan so much. To continue to bake after a tan is achieved is counter productive. You're aging your skin."

Both Potter and Dr. Peter N. Horvath, director of the division of dermatology at the Georgetown University School of Medicine, believe it's impossible to say exactly how much exposure to the sun is too much exposure, other than to warn burning is not a good idea.

"We do know that excessive suntanning and burning, particularly for women, will age the skin. It gives it a muddy appearance, uneven," says Horvath. "This didn't happen to our Victorian grandmothers because they stayed out of the sun."

Horvath says that women who make a fetish of tanning, who work at achieving an almost ebony hue by summer's end, "look 45 if you look at them at 40, and at 50 they look 55 or 60." Baking in the sun "ought to be discouraged, or if you're going to do it you ought to use a sun screen," which filters out the sun's burning and tanning rays.

Sun screening agents and blocking agents are commercially available. The screens simply decrease the amount of burning, or tanning rays - depending on the product - reaching the skin, and the blockers are supposed to provide total protection.

Some products now in pharmacies carrying rating numbers as part of a new system for determining what proportion of the sun's rays are filtered out. A number 2 product, for instance, halves the rays that reach the skin without the use of the cream.

Horvath recommends that anyone who has been in the sun for a prolonged period of time should use some form of moisturizer - such as a hand or face lotion, or baby lotion - on their skin afterward to help it combat the sun's drying effects.

And once you've achieved that tan, advises Potter, cover up. If you have to remain out in the sun, wear long sleeves and some form of pants to protect your legs. A wide brim hat to shield the head and face is also a good idea.

Sunburn, physicians warn, is just that. And while you may want to have fun in the sun, too much fun can lead to a real burn, complete with pain blisters, and peeling skin.

According to Horvath, those at a loss of what to choose when confronting the massive display of lotions, creams, salves, ointments, screens and blockers in many pharmacies would do well to call the American Cancer Society before heading for the beach. They provide you with a list of products that they say really work.