THE CAMPAIGN BEGAN in the summer of his 11th year, shortly after we moved in a house at the bottom of a hill in a nice, suburban neighborhood. There were several other boys his age living there and they all had them. One was even subscribing to the magazine. By August the campaign was annoyingly intense: all he wanted for Christmas was a new skateboard.

Not just any skateboard. Not the $8 ones that were on sale at the sporting goods store and not the $14 or $16 ones assigned special display places in department stores, and he certainly wouldn't be caught dead anymore on the green plastic skateboard we'd gotten him the previous winter.

What he wanted was a real skateboard, a fiberglass one with trucks and wheels, the kind that you design yourself and custom order from the Right Store, the kind that does not cost a cent over $70.

August, I pointed out at the top of my voice one day, was four months away from Christmas. He took the hint and we didn't hear much from skateboards until November when the campaign started up again. Copies of Skateboarder magazine mysteriously appeared on the kitchen table at breakfast and on the nightstand at night.

Young men, 12 and 13 years old, would drop in to visit and start chatting up their skateboards. Boys, whose previous conversations with me consisted of Hi and Thanks when offered something to eat, suddenly turned into eloquent orators. Skateboarding, it seemed, was not just fun, it was good exercise. Devising new tricks was mentally stimulating. Here was a chance for them to lear firsthand the basic laws of physics.

And it appeared none of them had ever been injured skateboarding. This sport that the newspapers were saying was so unsafe was fine for the kids on our block. They were careful. They knew what they were doing. The hills weren't that steep. I remember showing my son the front page newspaper story in which the Consumer Product Safety Commission predicted 375,000 skateboard injuries in 1977. And I remember the baleful look and the tired voice stretching the words "Oh, mother" into italics of despair.

We gave in. The skateboard that appeared under the tree the Christmas of 1977 was a real skateboard, made of bright yellow fiberflex, with expensive trucks and royal blue 65 millimeter Kryptonic wheels. It was truly a thing of beauty. For $84, it ought to be.

The skateboard became a most cherished possession. It went inside in the dark days of winter and emerged in April, reuniting friends on the slopes of the subdivision. Here was a welcomed rite of spring at a time in which we see ravaged teen-agers hanging out in drugstores, skipping school and dumping bottles of beer in supermarket parking lots at 9:30 in the morning. In times such as these, it was particularly reassuring to see bright, healthy kids gliding down the hills at twilight, eyes shining, arms stretched out for balance, turned on by the natural speed of their own motion.

I wasn't home when it happened. Later, at the hospital, he told me the trucks on the board were too loose. He fell onto the street and by the time I got home, about 15 minutes later, two lumps the size of golf balls were rising menacingly on his left wrist under the icepack my husband had put on. The ride to Arlington hospital's emergency room over bumpy roads at dusk caused him excruciating pain.

The X-rays confirmed the obvious: the break was near the wrist, in the growth plate, which meant it would heal quickly. The doctor injected a pain killer into the wrist and the kid who had handled pain so well up until then, suddenly went white. Minutes later they held him firmly and straightened out the bone in his arm. The injection did not really help. We never got dinner that night. By the time we got home at midnight, he didn't have any appetite.

The permanent cast went on this week, eight days after the accident. The doctor says it will be on another three weeks, but the pain has finally diminished and my son no longer needs pain killers. The cost has been high: someone who thrives on independence now needs help buttoning buttons and tying shoes; a kid who was the goalie on a select soccer team is out for the rest of the season; a kid who swam every day and who was looking forward to the summer swim league is out of training, grounded, and presumably out of a competition he loves.

The cost of letting a child skateboard, of giving in, is higher than you realize until you spend the night with him in pain at a hospital, higher than you realize until you hear the doctor treating him tell you that his wife's cousin was killed when his skateboard travelled into a moving car.

The Consumer Products Safety Commission is suggesting that finally some parents and kids are saying it's not worth these costs. A commission staff paper quotes Money magazine to the effect that skateboard sales were down 50 percent in 1978 in comparison to 1977. Injuries are declining. In 1973, there were 3,682 people treated in emergency rooms for skateboard injuries. The number rose to an estimated 140,070 in 1977 but dropped dramatically to an estimated 87,000 in 1978. Almost 65 percent of those injured were between the ages of 5 and 14 and over 70 percent of those injured were boys.

The commission staff recommended against a petition to ban skateboards, arguing that the popularity of the sport is declining at the same time that those kids still doing it are using skateparks and off-street skating sites, and protective equipment such as knee and elbow pads and helmets.

The kid wants to get elbow pads now but says he won't wear a helmet. Ask him what he'll do if he breaks his arm again and he says, "I will definitely not skateboard anymore" and then he promptly retracts that absolute.

He has every intention of getting back on his skateboard again. Soon, we will be locked in another battle of wills, facing another campaign with us as parents knowing even more this time about how dangerous a skateboard can be. The question is, will we give in again? CAPTION: Picture, no caption, UPI