When the sleds come out, the bikes go away. But a physician who checked figures on head injuries resulting from sledding thinks one piece of bike equipment should stay--the helmet.

If America's kids would wear helmets when sledding, thousands of head injuries each year could be avoided, said John R. Tongue, of Tualatin, Ore.

"Head injuries from sledding are certainly preventable," said Tongue, who studied the issue for the American Academy of Orthopaedic Surgeons (AAOS).

Data compiled by the Consumer Product Safety Commission show that approximately 7,000 sledders ages 16 and under are taken to hospital emergency rooms each year to be treated for head injuries. "Forty-three percent are brain injuries and a third are serious, so you are talking about a serious problem," Tongue said.

Other types of helmets also could prevent injury, but bike helmets are inexpensive, commonly available and capable of doing the job, Tongue said. "Bicycle crashes occur at higher speeds than sledding injuries," he said.

The risk probably is greater among younger children, whose necks are weak and heads are large compared with the rest of their bodies, Tongue said. Also, they are newer to sledding and probably are not paying as much attention as they should to such potential dangers as the sledders behind them, he said.

Although bike helmets weren't created for sledding protection, cyclists and sledders have similar types of accidents: They strike something, go forward and tumble off. Tongue feels sure the helmets would be protective.

Parents would have to make some adjustments in the bike helmets to make them fight right and keep their children's heads warm, however.

A cloth cap--possibly a tight fleece--could be worn under the helmet to keep body heat from escaping through the helmet's vents, Tongue said. Also, the straps might have to be readjusted to be sure the helmet fits properly with a cap inside.

If the helmet is too tight, it may be time to buy a new one, Tongue said.

The idea of using bike helmets when sledding deserves consideration, said Frederick Rivara, a Seattle physician who has studied bike helmet use. His 1992 study of Seattle-area injuries showed no decreased risk of head injury among children who wore helmets while sledding. But the study cautioned that there may have been too few children in helmets to make the analysis meaningful.

"My guess is that they are probably protective, and there's no way they could be harmful," Rivara said.

The AAOS's national safe-sledding campaign recommends helmet use as well as not going down headfirst, and sledding away from streets and with adult supervision, in areas free of such hazards as rocks and fences.

Tongue also is working with the Pacific Northwest region of the National Forest Service (NFS) to promote sledding safety, including helmet use. The agency has ski and sled runs on some of its land.

Ski slope operators can make sure their areas are well-groomed and monitored, but in unregulated areas "the family just dives off the hill, and we can't manage it," said Temple Tait-Ochs, the NFS safety manager for the Pacific Northwest.

At two managed sled runs near Mount Hood, Ore., sledders are given free use of ski helmets, said Charlie Wessinger, operator of the Summit ski area.

Only about 5 percent of sledders choose to use the helmets, Wessinger said.

"That's real low, but two years ago, it was zero percent," he said.