LAST WEEKEND, running in a 10-kilometer race on the Mall, one young man nearly died of heat stroke. He was lucky on two counts: another runner nearby happened to be a doctor, and an ambulance responded rapidly. Heat stroke gives little warning, and is a very quick killer.

A generation accustomed to air conditioning sometimes forgets that working out under the sun in a Washington summer can be worse than uncomfortable. When the temperature goes over 80, the need for caution rises sharply. The danger of heat stroke is greatest for the elderly, but youth is no guarantee of safety. The man running on the Mall was in his early 20s. The memory of the disastrous race on a hot day in Herndon three years ago in which two runners died--one of heat stroke, one of a heart attack possibly induced by heat--seems to have faded. But the weather doesn't have to be spectacularly hot to raise the risks of sustained exercise like distance running. The race on the Mall was early in a day that, by the standards of a Washington summer, was not unusually warm.

There are precautions that need to be taken both by people who run and by those who organize races. In the kind of weather that Washington enjoys from June through September, sensible people slow down and cut back a bit. Drinking plenty of water is important, and so forth.

But the responsibilities of race committees go a little farther. In this season, it ought to become standard practice to have qualified medical help-- physicians or paramedics--available on the course. It's not good enough simply to keep leaving it to luck. Last weekend's near-miss was not an isolated event. There were some 4,500 people in that race, and experience suggests that when the humidity rises, out of 4,500 runners, someone will need help. When that happens the next time, will help be there soon enough?