The AARP, the would-be hip organization that must have coined the phrase "Fifty Is Nifty," would like all you oldsters to know: Not only can you run marathons and climb mountains after hitting the mid-century mark, you also can have great sex. In fact, many of you already do.

And, according to its own research, many of you don't.

At a press conference yesterday, AARP titillated a pack of reporters desperately seeking stories in August with a national sex survey commissioned earlier this year. Among the highlights touted: Many women under 60 don't feel they have to have a wedding ring to jump into bed. Men and women find their partners more physically attractive over time. Both have sex more frequently than previously thought.

"The biggest myth is that old people don't have sex," said Hugh Delehanty, the new graybeard editing AARP's magazine, Modern Maturity, whose entire September-October issue is devoted to sex, including the cover piece, "Great Sex: What's Age Got to Do With It?"

Delehanty, however, defines old as anyone over 45, the age at which the poll sampling began. Perhaps it's the 45-plusers that the magazine is aiming for with a voluptuous Susan Sarandon on its cover and articles such as "Intimacy 101," "From Lib to Libido," "Touch and Go" and "Who's Sexy Now."

In reality, a significant number of older Americans--60 and above--reported having less and less interest in sex.

The importance of sex to quality of life, for example, drops dramatically as you age, especially for women, according to the AARP survey, which was conducted by National Family Opinion Research Inc. Almost one out of 10 women ages 45-59 told surveyors they would be "quite happy never having sex again." By age 60 to 74 that proportion was one out of four; by age 75-plus, one out of three.

Women also were far less likely than men to report having sexual desires. One out of five in the 45-59 age range said they felt such desire "less than once per month" or "not at all." By age 60 to 74, that proportion had risen to almost half.

Susan Jacoby, author of the "Great Sex" piece for Modern Maturity, said she believed women's declining interest in sex in the later years can be traced to the lack of available men. "They are accommodating to reality rather than what they would like," she argued.

About half of the men and women in the youngest age group said they had had intercourse at least once a week over the previous six months, but that proportion dropped dramatically among the older groups. Among women over 75, four out of five had been celibate during the previous six months and two out of three reported no kissing or hugging. "I find that very depressing," Jacoby said.

The depressing news for men in this survey was that one out of three in the youngest group, and the majority in the two older groups, reported some degree of impotence. And only one-fourth of those who said they were impotent said they took medication to spice things up, a finding the AARP staffers found astounding given the media frenzy over Viagra.

Because the AARP's sampling began at age 45, and their largest age group was the 45-to-60-year-old bunch, the poll's mean age was 60, or seven years younger than the average AARP member. AARP membership begins at age 50.

Didn't this swing the overall results toward more friskiness than the average older person experiences? Constance Swank, research director, would say only that the organization dipped five years below the AARP bar because it wanted to compare the attitudes and behavior of baby boomers with the older populations.

The majority of both groups, it seems, are happy with their sex lives, or lack thereof. Maybe that's because they have other priorities, including good health, satisfying family relationships and financial independence.