Washington area stores are bursting with sun screens. There are lotions, oils, creams, gels and butters. There are special sun screens for lips and for faces. There are blends, formulas--even a bottle of dial-a-tan.

All the products, which are getting maximum shelf space with the arrival of the tanning season, carry the promise of suntan without sunburn.

But there is still a problem: how to choose the best buy for your skin from the crowded, confusing displays?

It's not difficult if you take a few minutes to learn the sun screen rating system and study the effectiveness ratings published in the June issue of Consumer Reports magazine.

Taking time now--before the Memorial Day weekend outing to the beach, the park or the back yard--to research the sun screen question could save money and pain.

Consider:

* Nearly all sun screens have a Sun Protection Factor (SPF) rating number that helps you select the one most suitable for your skin. The higher the number, the more it blocks the sun and the more protection you get against a burn. Because you need more protection when you start a tan, you may want to begin with a high number product and then drop to a lower number as you build up protection.

* Some sun screens wash off and must be reapplied frequently, after each dip you take in the water or after you have perspired from a game of beach volleyball.

Because a thorough application of some sun screens can cost as much as a couple of dollars and you risk a burn when the sun screen washes off, the most water-resistant sun screen is the best buy. The accompanying chart shows the sun screens that Consumer Reports found to be most water resistant.

* Types of sun screen products--lotions, gels, creams--simply give you a choice, according to the Food and Drug Administration, which regulates the sun screen industry.

"It depends on your personal preference, just like deodorant," an FDA spokesman said. "You may like a spray deodorant and someone else likes a roll-on deodorant. So some people like lotion sun screens and others like oils."

There is a wide range of prices for sun screen products, and some of the best are the least expensive.

In a random sampling of prices at Washington stores, for example, the lowest price found was $1.08 an ounce for the Alo Sun Fashion Tan, a product that Consumer Reports found to be among the most water resistant.

The most expensive sun screen in the survey was $2.60 an ounce for the Clinique Sun Block, which was found to be less water resistant than several other sun screen products.

The magazine singled out one sun screen--MMM! What A Tan!--as a best buy, based on its price (68 cents an ounce in the magazine's price check) and it's water resistance. But MMM! is no longer manufactured, said its manufacturer, the 3-M Co. of St. Paul, Minn.

Here is a summary of how the SPF rating system works, from FDA:

* SPF 2 to 4: Minimal protection from sunburning but permits suntanning. Recommended for people who rarely burn and tan easily and deeply.

* SPF 4 to 6: Moderate protection from sunburning; permits some suntanning. Recommended for people who tan well with minimal burning.

* SPF 6 to 8: Extra protection from sunburning; permits limited suntanning; recommended for people who burn moderately and tan gradually.

* SPF 8 to under 15: Maximum protection from sunburning; permits little or no suntanning; recommended for people who always burn easily and tan minimally.

* SPF 15 or greater: Offers the most protection from sunburn; permits no suntanning; recommended for people who burn easily and never tan.

Some sunbathers experiment, blending several products to suit their skin and using various products for different parts of their bodies--a 15 for noses that burn easily, for example, and a four for shoulders that need less protection.