Twenty-five years ago, when Dr. Robert Butler began doing research on aging, the two subjects he found hardest to discuss with elderly people were death and sex.

"But those were the two topics they wanted to talk about most," says Butler, now director of the National Institute on Aging Part of the problem was a social prejudice that "veiwed sex for the elderly as a matter of ridicule, using labels such as Dirty Old Man or Ulgy Old Biddy."

Today, however, there is "a slowly increasing pubic acceptance of sexuality in later, life," Butler told about 100 sex counselors and educators at a meeting of Washington's Sex Education Coalition.

"Training programs, conferences and publications for physicians, sex counselors and psychotherapists are beginning to include the problem of older people, as well as those of the chronically ill and physically disabled of all ages.

"Even some nursing homes are relaxing their puritanical standards by introducing 'privacy rooms' where older people can be alone together. There is a growing recongnition that. . .romance and sex are still a vital concern for some."

Butler, who co-authored "Love and Sex Afer Sixty" with his wife and collegue, psychotherapist Myrna Lewis, stresses that "it's not essential that all elederly people feel compelled to be interested in sex."

But those who do, he says, "should not be restricted form natural expressions of intimacy. In the normal course of aging, women ordinarily do not lose their physical capactiy for orgasm, nor men their capacity for erection and ejaculation.

"What we do see is a gradual slowing of response, especially in men -- a process currently described as part of 'normal' aging, but perhaps itself eventually amenable to treatment and reversal. A pattern of regular sexual activity, or at least self-simulation helps to preserve sexual functioning in both men and women."

Societal disapproval of sexual drive in the elderly, Butler notes, may cause some older people to give up on sex. If an adult child strenuously objects to a widowed parent's dating, or if a nursing home humiliates residents who make sexual advances, the older person might capitulate.

But "probably the majority of the old, who are interested in sex," he says, "want the opportunity for it and would welcome help with the physical, emotional and social problems that interfere with its enjoyment."

When sexual problems do occur among older people, "they should be viewed as the result of physical disease, disability or emotional upset," says Butler, "requiring careful diagnosis and treatment to restore functioning."

Among common factors, according to Butler, which affect sexuality in older people:

Heart Disease : "especially if a heart attack has occured, leads many older people to give up on sex altogether for fear of provoking another attack. oYet the incidence of death during sexual intercourse is thought to be very low.

"Sex usually can, and in many cases should be resumed an averge of 16 weeks after a heart attack, depending on physical conditioning. An active sex life may in fact decrease the risk of further attack."

("A test to determine readiness for sex," says Butler, "is whether or not a person can walk vigorously for three blocks, or climb one or two flights of stairs without pain, abnormal pulse rate or blood pressure or electrocardiorgam changes.")

Anemia : "produces one of the most common and easily treated sexual problems. Found in some form in one out of four persons over 60, anemia leads to fatigue and often a reduction in sexual activity. An improved diet with adequate vitamins and mineral will frequently restore both energy and sexual activtiy."

Drugs : "can cause sexual problems. Tranquilizers, anti-depressants and certain anti-hypertensive drugs are all culprits. A doctor can often presctibe a less sexually-inhibiting drug if he or she realizes this is important to the patient."

Alcohol : "in excess reduces potency in men and delays orgasm in women and is probably the most widespread drug-related cause of sexual problems. In general, an older person should not have more than 1 1/2 ounces of hard liquor, two 6-ounces glasses of wine, or three 8-ounces glasses of beer in any 24-hour period when sex is anticipated."

Emotional problems : "the fear of impotence. . . All men of any age are impotent from time to time. . . But if a man is unduly alarmed by temporary impotence, or in the case of older men, by sensing a gradual slowing of sexual response, he may cause, or perpetrate the impotence through fear alone."

Older women tend to be worried more "about the propriety of sex itself in their later lives. . . There can be emotional problems between older sexual partners: sexual boredom, a change in emotional balance due to illness, the unrelenting intimacy of retirement, or simply the same problems that affect couples of any age."

Of specific concern to older women, says Butler, is the shortage of older men. Because women outlive men and most marry men older than themselves, "over 60 percent of older women have no martial partners, in contrast to about 20 percent of older men. Chances of remarriage are slim for women while excellent for men."

To deal with this sex-ratio imbalance, older women are exploring various options, Butler says, such as "a greater number of relationships, and in some cases marriage with younger men. Some women are revealing affairs with men as much as 40 years younger than themselves just as older men have long done with younger women.

Other trends:

"Relaxation of female inhibitions against fantasy, masturbation, sexual massage. . .and greater use of male prostitutes for older women. Honolulu, Hawaii, has become noted among vacationing older women for the availability of paid sexual partners.

"Exploration of late-life homosexuality after a pattern of earlier heterosexuality and increasing support for women who have been lifelong, but hidden homosexuals."

While admitting that many people find it difficult to discuss sexual problems, Dr. Butler urges older people to communicate concerns to their doctors or to seek referral to a qualified sex therapist.

In the furture, he says, "Sex in the late years will be taken for granted. Then we will see for the first time the full life cycle of love and sexuality, with youth a time for exciting exploration and self-discovery; middle age for gaining skill, confidence and discrimination, and old age for bringing the experience of a lifetime, and the unique perspectives of the final years to the art of loving one another."