Although sleep patterns change with age, the homey image of an old granny nodding off over her knitting or a grandpa snoring in front of the TV may actually mask an underlying physical or psychiatric problem.

And while sleep problems appear to be widespread among the elderly, they are not a normal part of the aging process and should not automatically be treated with drugs.

Those were the conclusions of a panel composed of the nation's leading experts on sleep, who met recently at a three-day conference sponsored by the National Institute of Mental Health and the National Institute on Aging.

The widespread myth that older people need less sleep is simply not true, according to William Dement, a professor of psychiatry at Stanford University School of Medicine and a pioneering sleep researcher. "We think that the ability to sleep decreases with age much more than the need to sleep," he said.

Dement and other experts said that the need to go to the bathroom is cited as a major cause of awakenings at night, the frequency of which rises with age. Sleep disturbances also are caused by Alzheimer's disease, pulmonary or heart disease, arthritis and psychiatric disorders such as clinical depression, which is a major problem among the elderly.

They also noted that sleep fragmentation -- daytime napping to compensate for nighttime wakefulness -- can be harmful. For example, it may tend to isolate an older person who is up when everyone else is sleeping and just can't stay awake when other members of the family are gathered in the evening.

According to the report issued at the end of the conference, about half of Americans over age 65 complain of sleep problems, often involving nighttime arousal and daytime sleepiness, the "flip side" of insomnia.

"In healthy older people without an accompanying medical disease, there are very few complaints of sleep disorders," said Robert J. Joynt, chairman of the NIH panel and vice president of health affairs at the University of Rochester. Emotional and social factors, such as retirement, also can play a role.

Although the elderly represent 13 percent of the population, they account for about 30 percent of the sleeping pills consumed in this country, the panel said. These drugs, which include tranquilizers like Dalmane or Halcion, can create problems of addiction and withdrawal, which exacerbate insomnia and can cause memory impairment and, on occasion, psychotic behavior.

Halcion, the most widely prescribed sleeping pill in America, received tough criticism from Anthony Kales, chairman of the psychiatry department at Pennsylvania State University's Hershey Medical Center. Kales said that "many reports of amnesia, daytime anxiety, delirium, memory impairment" over the past 10 years made use of the drug highly questionable. Even though the manufacturer has produced a lower dose of the drug, said Kales, it just means that "now we're down to a dose which is relatively ineffective, yet retains many of these adverse alarming and frightening side effects." They are particularly insidious, Kales said, "because one does not know when amnesia is occurring unless one is told by friends or co-workers."

It is true, said Charles A. Czeisler, a neuroendocrinologist at Brigham and Women's Hospital in Boston, that the circadian rhythms that govern sleep and waking, among other rhythmic bodily functions, tend to weaken in the older person. The circadian pacemaker in the brain, which was identified in the early 1970s, is a tiny cluster of neurons at the tip of the hypothalamus. It has the same function that the pacemaker has on the heart, Czeisler said. But as a person ages, the brain's pacemaker seems to move out of synchronization with the 24-hour day to which it is basically attuned when a person is younger.

"What happens," he said, "is that a person retires with the idea that now he'll sleep as long as he likes, after 30 years of having to get up at 6:30 to get to work. And then he still wakes up then or even earlier." The reason: His body clock simply will not cooperate with his new-found leisure.

Czeisler and his team have shown recently that the use of light can sometimes modify circadian timing that is disrupted because of jet lag, shift work or aging.

Older people also are more prone to a disorder known as obstructive sleep apnea. Sleep apnea, which affects more men than women, causes its victims to snore and then stop breathing. Breathing resumes when the person wakes up and begins breathing again. In extreme cases, this process occurs hundreds of times each night and, obviously, does not make for restful sleep. It also can cause blood pressure to soar and make the victim fall asleep the following day at inappropriate and sometimes dangerous times -- such as behind the wheel of a car.

In severe cases, the chronic lack of oxygen to the brain can cause cognitive and memory problems. Some sleep specialists believe it is a cause of some dementias that might be reversible.

Because apnea also is associated with obesity, sometimes losing weight can control it, the panel said. In addition, avoiding alcohol and sleeping pills are recommended.

Underlying much of the testimony at the conference was a sense that although specialists in sleep disorders have discovered diagnostic techniques and many successful treatments, the public and many physicians still tend to dismiss or minimize complaints about sleep problems among the elderly.

These problems, Dement said, are not confined to the elderly, even though they may be more pronounced among that age group. A recent study cited by Dement of people who maintained they were not sleepy found that 40 percent really felt drowsy and 25 percent were seriously sleep-deprived. "There are a lot of people who think they are functioning at a normal level, who are impaired because of lack of sleep," he said.

Although there are about 100 different sleep disorders, he continued, "older Americans do not have access to the benefits of sleep research." The barriers, he said, are cost and ignorance on the part of both the public and physicians about sleep.

Joynt's conclusion, shared by the panelists, was succinct: "Knowledge about sleep and its disorders is lacking, and education is needed at all levels."

Howard P. Roffwarg, professor of psychiatry at the University of Texas Southwest Medical Center at Dallas and current president of the American Sleep Disorders Association, talked about what he called the "sleep dishygiene" activities of older people that could disturb the circadian rhythms and weaken the capacity for sound sleep. These included caffeine and alcohol consumption, too much time spent in bed and worry at bedtime.

"Mother," he said, "never told us not to try to solve the planet's problems when we're trying to go to sleep."More information: American Sleep Disorders Association, 604 2nd St. SW, Rochester, Minn. 55902.