Once, long ago, barbarians kicked the heads of their fallen adversaries around a field. Some say that was the origin of the sport that we call soccer (and most of the rest of the world calls football). Now, of course, we use balls, not skulls, and although the most popular ball in use nationwide is made of black-and-white synthetic leather, you can buy many color combinations in real leather, synthetics or rubber.

Today's soccer balls come in different sizes according to the needs of the players. Size 3, for example, for young- sters 3 to 8, is the smallest regulation playing size, measures 231/2 to 241/2 inches in circumference, and weighs from 101/2 to 12 ounces. Size 5 for high school, college and professional play has a circumference of 27 to 28 inches and weighs 14 to 16 ounces.

Soccer writer Gary Rosenthal says the early soccer ball was made of eight leather panels, with an inflatable rubber bladder inside it. Because the leather panels stretched, ball manufacturers began producing a 16-panel ball and then the 32 pentagon-shaped panels used in most of today's soccer balls. Modern stitching and waterproofing make soccer balls last longer and play better, but if you play with a good leather ball, remember to deflate it slightly after use so air pressure does not stretch the panels and stitching.

Soccer International Inc. in Arlington offers all the balls pictured below as well as a variety of products, gifts, uniforms and training aids for players, officials and coaches, most at discount prices and most shipped the day after the company receives the order. Balls shown below range in price from the Mikasa Kick-off/SWL 310 (six for $115) to the Select Super Brillant hand-sewn leather soccer ball from Denmark, which Soccer International sells for $62.50 (discounted from $90).

Soccer equipment and gifts. (Color eight-page catalogue, $1.) Soccer International Inc., Box 7222, Dept. WPT, Arlington, Va. 22207. Call 524- 4333 from 10:30 a.m. to 10 p.m.