Unless you have a short memory or spent last summmer abroad or in a meat cooler, you probably do not need to be reminded about the debilitating effects of day-after-sticky-day of temperatures over 90 degrees. And you may also think you do not need to be reminded about how best to cope with oppressive heat and humidity to enhance your comfort and preserve your health.

Even those who should and do know better often ignore the warnings and fail to take even the simplest precautions to protect themselves against illness caused by overheating. Every summer tens of thousands of people end up in the hospital and many die after being overcome by the heat.

Just last week Alan Greenspan, chairman of the Federal Reserve Board, was taken to a hospital with heat exhaustion after playing tennis in the hot sun. Mr Greenspan, 63 years old, was treated overnight at the hospital.

Even if this summer is nothing like the sizzlers of the past, there will almost certainly be some oppressive days ahead. Appreciating the effects of heat on your body and knowing how best to mitigate them can increase your comfort and productivity. It may even save your life. Responding to Heat

The human body is far better able to withstand extremes of cold than extremes of heat. The body's core temperature, normally 98.6 degrees Fahrenheit, can drop to 60 degrees without fatal effects, but few if any would survive a rise above 110. In effect, proteins and enzymes throughout the body are destroyed by cooking, and organs suffer irreversible damage.

Humans are born with several cooling mechanisms. The heart pumps more blood to the outer reaches of the body, and surface blood vessels dilate so heat can dissipate. Heat is also lost through exhaled air. Both these mechanisms become ineffective at air temperatures above 92, the usual temperature of the skin.

Sweating is another safeguard. Actually, it is not the sweat, but the evaporation from the skin surface. The heat needed to vaporize sweat is taken from the body.

When humidity is high, meaning air is laden with moisture, this method of cooling becomes ineffective. Generally, at 60 percent humidity sweat will not evaporate. But even in high humidity, the slightest breeze will cool you by lowering the temperature of the sweat and increasing evaporation as a greater volume of air passes across your skin. Heat Is a Killer

Official statistics, which reflect only those deaths indisputably caused by excessive heat, belie the actual toll of hot weather. Figures for last summer have not yet been compiled, but the number of deaths attributed to the heat in an unusually hot season can reach 1,500 in this country.

In fact, the heat probably hastens or precipitates the death of more than 15,000 people in such a season. This would include many elderly people and infants, who are less able to adapt to heat; people with chronic ailments like heart disease or diabetes that interfere with the body's ability to cool itself and people taking certain medications that exacerbate the heat's harmful effects.

For example, an aging cardiovascular system or one damaged by diabetes is less effective at getting large volumes of blood to the skin. Diuretics reduce blood volume, and phenothiazine tranquilizers, antihistamines and antidepressants reduce sweating. Cardiovascular drugs like beta-adrenergic blocking agents and vasodilators, which dilate the blood vessels, can also heighten the risk of heat damage by slowing blood flow to the skin where it can be cooled.

Others at high risk of heat's damaging effects include people with kidney disease, hypertension and skin disorders like scleroderma, eczema and healed burns. People who are very overweight are also at risk, as are alcoholics; people who have suffered heat syndromes in the past, and those taking drugs to control epilepsy or Parkinson's disease, which can impair sweating ability.

Infants and small children are vulnerable because they sweat less, their hearts are less able to pump large volumes of blood and they generate more body heat during ordinary activities than adults do.

But even perfectly healthy, lean and fit individuals can succumb to heat. Heat exhaustion is relatively common among marathoners. Those who push too hard and drink too little during a long race or other vigorous outing can suffer soaring body temperatures and die of heat stroke.

Millions of television viewers saw a dramatic example of heat exhaustion in the 1984 Olympics in Los Angeles. Gabriela Andersen-Schiess, representing Switzerland in the women's marathon, staggered and weaved across the track after entering the stadium to finish the race. She collapsed after crossing the finish line and was treated for heat exhaustion and dehydration.

Athletes are often inclined to push themselves to do more than their bodies can tolerate in hot weather. Doubly foolish are those who wear plastic suits in hot-weather workouts, which increase sweating (and dehydration) but prevent body cooling. Signs of Trouble

Early symptoms of heat stress -feeling hot, uncomfortable and listless - are rarely heeded. But if they persist, they can lead to more serious problems: dizziness, rapid heartbeat, cramps, nausea, diarrhea, dry skin, throbbing headache, chest pain and breathing problems.