For the Veterans Administration, what's happening in Miami may be a sign of things to come.

Downtown, in the midst of one of America's retirement meccas, sits a 12-story VA Medical Center that must turn away scores of patients seeking outpatient services for everything from the flu to broken bones. With more than 280,000 outpatient visits last year, the center can handle only those veterans who must be cared for by law, not those who simply want to be.

"We're running at top speed," said hospital director Dr. Felipe Knopka.

"Miami could be the bellwether of what we're facing in the future in some of our facilities," said Dr. John Mather, the expert on geriatric care planning in the VA's Department of Medicine and Surgery.

Like the American population in general, more and more of the 30 million veterans are getting gray. Unlike the rest of the population, veterans have been granted a complex variety of benefits over the years. Chief among these is the opportunity for care (or the right to care, if military service left a veteran disabled) at the VA's vast network of medical facilities. The older the veterans get, the more likely they are to call on the VA for medical help.

It's a problem demographers have seen coming for years. Most veterans are products of wars, so they are clustered in certain age brackets -- groups who were young when the nation went to war. There were bulges in the veteran population after World War I and World War II, another bulge after the Korean War and another after Vietnam. Now the 12 million World War II veterans, with an average age over 62, are becoming senior citizens.

This year, 3.7 million veterans, 12 percent of the total veteran population, passed their 65th birthdays. By 1988, when the total number of veterans is expected to be slightly lower, the VA estimates the number of elderly veterans will grow to 6.7 million, or 23 percent of all veterans. By the year 2000, 9 million veterans, more than a third of all veterans, are expected to be 65 or older.

Five years ago, these figures had some VA officials making ominous predictions about the future strain on their medical facilities, particularly hospitals and nursing homes. Congress passed legislation authorizing seven new geriatric research and care centers, nearly doubling the present number. Between 1977 to 1981, construction bills for VA hospitals and nursing homes climbed dramatically, peaking in 1981 at nearly $400 million.

But when Donald L. Custis, director of the Department of Medicine and Surgery, came before a hearing of the House Veterans' Affairs oversight subcommittee this summer, he took a relaxed view of the prospects. Yes, there would be increased demand, he said, but "I do not believe the VA is going to be overwhelmed on any given day by demands to provide total care for all . . . veterans over 65."

How does Custis remain calm in the face of the statistics? In part, it is because experience indicates that only about a quarter of elderly veterans turn to the VA for medical help; in part, it is because while more than 9,000 elderly veterans are cared for in the VA's 91 nursing homes, another 16,000 are cared for in community or state nursing homes with the costs underwritten by the VA. That pattern is one the VA hopes will continue, particularly since the cost of care in community nursing homes is only a little more than half the cost in the VA's homes.

Last month, the VA set about getting more information about how the elderly veterans would use the VA's medical system. A $350,000 contract was awarded to the Louis Harris polling organization to survey elderly veterans and find out their financial status, the state of their health, the insurance they carry and their living situations. If, for instance, an elderly veteran needing some care lives alone or has only a frail spouse to care for him, his need for nursing home or domiciliary care may be greater than another veteran with younger family members at home.

"We"re looking at new modalities of care," said the VA's Mather. The aim, he said, is to keep the elderly veteran out of institutions and, if possible, help him learn to care for himself after a debilitating illness such as a heart attack or stroke.

Among the possibilities being explored for veterans who need some supervision but not hospital or nursing home care is the adult day-care center. The VA is cosponsoring two pilot day-care centers in Palo Alto and Loma Linda, Calif.

But one of the things that concerns Mather most is not where older veterans will go to get help for their medical problems, but the training of the people who will be there to help them. "Making nursing homes into teaching nursing homes will enhance the health care quality," he said. "We're organizing some education programs to prepare for this." The programs, he said, have to be geared to give doctors and nurses an understanding of the social and psychological needs of the elderly, not just the best ways to treat hypertension or repair a broken hip. Eight VA medical centers are hosting a program to train geriatric "teams" in these areas. And while keeping all the needs of the next 30 years in mind, the VA must remember that the boom in elderly veterans will level off in the early 2000s, before booming again when the Vietnam veterans near retirement. graphics /charts: THE AGING VETERANS POPULATION THOSE WHO SERVED AND THOSE WHO DIED TWP