Thousands of older Americans die every winter from accidental hypothermia--abnormally low inner body temperature--and even more suffer illness and extreme discomfort from it, witnesses told a congressional hearing yesterday.

The extent of the problem cannot be properly measured because most hospitals lack low-reading thermometers, which measure body temperature below 94 degrees Fahrenheit, the lower limit of normal thermometers, according to the testimony.

W. Moulton Avery, director of the Center for Environmental Physiology, said it is a "national disgrace" that most hospitals lack low-reading thermometers, which sell for $2 to $5.

Giving a "conservative" estimate, Avery said 25,000 persons die every winter from hypothermia "and the number is growing year by year."

Older persons are especially vulnerable, witnesses agreed, because they, along with newborns and infants, are least able to maintain normal body temperature in cold weather.

Dr. Nicholas Rango, an assistant professor of medicine at the Columbia-Presbyterian Medical Center in New York, said available data systematically underestimates the number of deaths from accidental hypothermia because the ailment cannot be properly diagnosed without a low-reading thermometer when a patient is alive.

When a person dies the body's temperature quickly drops to room temperature. As as result, accidental hypothermia victims often are incorrectly reported to have died from heart failure or some other cause, Rango said.

Rango and Avery pointed out that hypothermia first clouds the mind so the victim's judgment is impaired, rendering him or her unable to take measures to prevent the lethal consequences of accidental hypothermia.

Even a nighttime temperature of 64 degrees can be too low, Avery said, although victims may not realize it. The night is especially dangerous because room temperature drops, body temperature is more difficult to maintain when the body is prone, the body is relatively inactive and the lapse of consciousness that comes with sleep combine to increase the danger of dying from the cold, Rango said.

One remedy potential victims can take, Rango said, is to use electric blankets, which are energy efficient and "terribly, terribly important to getting people through the night."

Committee chairman Claude Pepper (D-Fla.) cited a University of Michigan survey of older persons that found that 18 percent of those surveyed reported making sacrifices to pay for heating fuel. Among those, the survey found, 40 percent said they sacrificed food and 16 percent said they gave up medical care or medicine.

Although energy consumption this winter is significantly less than in 1976-77, residential energy consumption was 8 to 27 percent higher than normal for January east of the Rockies, according to Dr. Thomas D. Potter, director of National Oceanic and Atmospheric Administration's environmental data and information service.

Potter estimated that energy consumption for this winter would be 6 percent higher than normal for the whole country.