What country has the most people age 65 or older? The most persons 80 years or older? The highest proportion of elderly?

Do you know what nation has the longest life expectancy at birth? What country by 2025 is expected to have the highest concentration of persons age 65-plus?The answers, as of 1985, respectively are: China (nearly 53 million Chinese age 65 or over); the United States (6.2 million Americans 80 years or older); Sweden (16.9 percent of its population over age 65); Japan (life expectancy at birth for Japanese is 77.1 years); and West Germany (by 2025, 22.5 percent of that nation's population is expected to be 65-plus).

These statistics are meant to spark planning for the future, says Kevin Kinsella of the U.S. Bureau of the Census who helped compile the figures.

Concerned about our nation's ability to meet the health and income needs of a growing elderly population, we often forget that the graying of America is taking place in an aging world, where one in every seven individuals will be age 60 or over by 2025. Yet in many ways, the changes occurring in America are mild by comparison to those challenging other nations.

"We need to begin thinking about solutions now," Kinsella says, "and looking toward Europe (there the older population currently ranges from 12.4 to 16.9 percent) may be the next step."

QUESTION: My mother recently fractured her hip. What causes hip fractures in elderly persons?

ANSWER: By age 90, approximately one-third of women and one-sixth of men will have sustained a hip fracture. In elderly persons they are usually the result of thinning bones and minor trauma usually caused by falls. The thinning of bone is called osteoporosis and is especially common in women after menopause, when the loss of natural estrogen allows calcium loss from bone. Both men and women also undergo bone calcium loss that is part of aging.

Additional risk factors for the occurrence of hip fractures include being of advanced age, female, white, and having had previous strokes and taken several drugs, especially psychiatric medications. Protective factors include obesity, estrogen therapy in women after menopause and, possibly, athletic ability. Many falls are preventable by making sure that objects are not left on the floor, and that stairs, railings and lighting are in good condition.

Hip fractures may occur in various parts of the femur, the long bone that runs from the knee to the pelvis. Proper treatment depends on the fracture site and severity of the fracture. Appropriate therapy ranges from bedrest and pain control to partial replacement of the hip joint. Better surgical results are achieved by delaying surgery until the person has been stabilized medically, usually two to five days after the fracture.

Antibiotics before (and for the first couple days after) surgery have helped prevent infections. People with hip fractures may develop blood clots in the legs which may then travel to the lungs, a life-threatening complication. Anticoagulation with blood-thinning medicine is often begun near the time of surgery.

Prognoses after a hip fracture depend on how healthy the person was before sustaining the fracture. Over half of people who fracture their hip will require convalescence and rehabilitation in a nursing home or rehabilitation center. Most people who were in good health before the fracture will be able to walk and return home within two to six weeks. A hip fracture may lead to complications and death for some.

For tips on accident prevention, "80 Do's and 58 Don'ts for Your Safety: A Practical Guide for Elder Care" is available free to veterans from the Veterans Administration (Safety Booklet, VA Medical Center (11-E), 16111 Plummer St., Sepulveda, Calif. 91343).

QUESTION: My 81-year-old mother recently fell, fractured her hip and required a hip replacement. I expected she would have to spend the rest of her days in a nursing home, but she is expected to return home in three weeks, following rehabilitation. Is she one of the lucky ones?

ANSWER: A study by Dr. Stanley Brody showed that of patients who had a hip replacement due to a fracture or severe arthritis and were discharged, 83 percent of those over 65 years returned home after an average stay of 30 days. Nine percent of this group were discharged to acute-care facilities, and only seven percent to nursing homes.

One innovative rehabilitation program, called "Easy Street," was developed at Phoenix Memorial Hospital and is now being franchised to hospitals by a private corporation. Patients negotiate a "commercial obstacle course," including curbs and bus steps, a newspaper vending machine and a bank teller accessible only by a cordoned path.

Not all rehabilitation programs take place in a hospital.