Sleep -- particularly the lack of it -- may have affected the outcome of countless battles over the ages. But the British campaign in the Falkland Islands eight years ago is believed to have been the first war in history in which sleep was considered as a tactical factor.

Air Commodore Anthony Nicholson of the Royal Air Force Insitute of Aviation Medicine and his colleagues devised sleep schedules for British pilots and crews in an effort to minimize sleep disturbances caused by the 7,000-mile flight from England to the Falklands. Through judicious use of a particular formulation of tamezepam, a tranquilizer that is a kind of sleeping pill, combined with stopovers at the approximate halfway point -- Ascension Island -- enough rest was provided, British sleep scientists found, for the flight crews to avoid the decrease in performance that results from too little sleep.

Col. Gregory Belenky, a psychiatrist who is chief of the behavioral biology department of the Walter Reed Army Institute of Research in Washington, has been performing sleep research for the past 20 years.

In testimony last month before the National Commission on Sleep Disorders Research, a congressional advisory group, Belenky, who emphasizes that his work is not related to the situation in the Persian Gulf, said that "whereas the body can do with just rest, the brain needs sleep." There is, he said, a 25 percent drop in the ability to think, plan and execute with every 24 consecutive hours in which a person is awake. After 72 hours without sleep, the ability to function cognitively is reduced by 75 percent. Fragmented sleep, Belenky said, may not be sufficiently recuperative.

Belenky cited two studies that he said demonstrate the potential for disaster that sleep deprivation can cause.

The first was a 1976 British study, "Exercise Early Call," in which infantry soldiers were tested shooting at targets when they were well rested and then after 72 and 96 hours without sleep. When the targets were fixed, the soldiers were able to shoot as well even after prolonged sleep deprivation. However, when they were put on a range where targets popped up at random their performance plummeted; some troops fell asleep, while others suffered from slowed reflexes or failed to see the targets in time.

The second, performed on a helicopter simulator at Ft. Rucker, Ala., showed that sleep-deprived pilots flew 50 or 60 kilometers beyond the point where they were supposed to change course. "They made catastrophic sorts of mistakes," he said.

Belenky also said that although he was unaware of specific sleep studies conducted during the Vietnam War, the clinical literature from World War II, Korea and the 1973 Arab-Israeli War indicates that combat stress casualties were almost always associated with sleep deprivation. One of Belenky's current research projects involves determining why prolonged wakefulness impairs the functions of the brain.

It is reputed that Tartar warriors slept on horseback while traveling from one raid to the next and prided themselves on staying awake for days. Admiration for the need of minimal sleep is not uncommon in even modern armies. That, says William C. Dement, chairman of the National Commission on Sleep Disorders Research, "is the kind of thing that has to change."