WHAT YOU see first at Leisure World are the golf carts. They are everywhere: parked in garages, rolling in eerie silence along the roads, waiting in line at ''Golf Carts Cross Here'' places on the main stree, and all over the 18-hole golf course that is the community's centerpiece.

In the afternoon they collect at the edge of the course by the clubhouse while their owners stop in for a card game or a drink at The Stein.

"I'd say more people own golf carts than own cars," remarks Robert Sullivan, who manages this very special village of 4,300.

In the Leisure World instruction booklet, two whole pages are devoted to golf carts.

Everyone knows how it was in the classic American suburb and still is in the new ones: You never see anybody old. It's all young families separated from their roots (the farm in Iowa with the three or four live-in generations and the uncles and cousins down the road and the sense of structure, order, place, Family), and some kids get to the third grade literally without ever seeing anyone with white hair, let alone black skin.

Well, the old folks are fighting back. They are fencing themselves in on their own rival reservations. You want to continue the breakup of the American family? Patronize the "senior citizen" right out of the culture? Reduce him -- or her, it's mostly her -- to a free baby sitter, a lap to regress to, a walk-on in your life movie? Look out.

You can't live in Leisure World -- it's that place on outer Georgia Avenue with the huge steel globe out front -- unless you're 50 or older. It's in the bylaws. It used to be 52, but times were tough in the early years, so they had to broaden the base. Now it's filling up nicely.

You can visit, to be sure, if you're under 50, but for no more than 90 days in a year. "And no guest who is younger than 16 years of age may reside in the community for more than 30 days in the calendar year."

One resident, a widower, married a woman under 50. He had to sell his unit and move out.

The first surprise is that more than half the people who move here still go to work.

"These folks come from $125,000 homes," says Ingo Thors, project sales manager for a new garden apartment complex at Rossmoor. "They've got money left over. It's the most interesting thing I've seen in my 12 years in real estate. I live here myself. Security and independence are the main attractions, that and the social amenities. And no maintenance!"

Many of the new residents call it Rossmoor. It doesn't sound as geriatric as Leisure World. You can live in a regular suburban home, a condo or cooperative, or, in about a year, a high-rise tower apartment. At Rossmoor you get:

* A fenced city with a gatehouse and 24-hour guards.

* A golf course, a clubhouse with restaurant and bar, game and hobby rooms, an outdoor pool, a chapel, a library, an outpatient facility and equipment for the 76 organizations that have sprouted since the place opened in August 1966.

* Free local minibuses and a travel service that gets you to the shopping centers, downtown Washington or Sri Lanka.

* Trash collection, snow removal, exterior maintenance, and water all taken care of, and plumbing and electrical repairs at half the normal cost.

* Self-government by 17 mutuals or neighborhood associations, which keep an eye on laggard guests, unleashed pets, unauthorized shrubs or vegetable gardens, illegal parking and other nuisances, and also make decisions about the commonly held property.

Rossmoor is not exactly a new way of life -- developer Ross Cortese started building Leisure Worlds in southern California more than 20 years ago, and today there are at least four others in operation -- but you might think it would take a bit of adjusting.

Not so, say the veteran real estate salesmen, who hear it all: People worry about possessions more than life styles. Where they're going to put that picture.

Some newcomers have planned their lives and look forward to moving in. Others don't think ahead and suddenly find themselves widowed, with a huge house in Kensington or someplace, whereupon their children, not wanting to be bothered thinking about them, sell the house and dump them in an apartment.

The difference at Rossmoor is that the apartment comes with a window onto a whole little community of peers.

They tell of one man, brought here after his wife died, who "didn't know what was happening to him and just moped around, still in grief and all. Three weeks later we saw him again, and he looked 20 years younger. He was a different person."

Most apartment developments figure on a 15 percent dropout rate. It's almost nothing here. Seven out of 10 residents owned their own homes at the time they came, and most of the rest used to own homes but had already sold them to move into apartments elsewhere.

Almost a quarter of them had retired to Florida but came back to be near their grown children, according to a survey. Nearly half are professional or technical people, and one in five is a managerial type.

What brings them here? Many say it's the security. When you have a guest coming, you have to tell the guards or they won't let him in. Though neighbors keep such a sharp watch for strangers that you probably don't have to lock up at all, the Leisure World guidebook recommends "charlie bars" on all sliding doors, and other urban precautions.

On the other hand, a survey taken last year for the developers of The Greens, a high-rise complex of 2,500 units in 10 buildings to be started next spring on and around the golf course, found 85 percent came here mainly for the freedom from maintenance. This study said that while newcomers are indeed mostly still working, when you take in the whole picture at Rossmoor with its longtime residents, you find eight out of 10 are retired and only about eight out of 100 people are under 60. True, the survey's 70 percent response rate might have been somewhat skewed by more replies from the retired stay-at-homes.

And the people who live here: Do they like it?

They love it.

They love it aggressively, ferociously. They grab you by the throat to tell you how much they love it.

"I'm busier than I ever was when I worked," exults Phil Rothchild, a former assistant commissioner for the Internal Revenue Service. "When we were still living in Colesville and waiting for the house to be built, I joined the Fun and Fancy Theater. I talked Miriam into it, and she did a bit part and stole the show."

Now Miriam Rothchild is president of the group. She also paints and designs scenery.

And when not appearing in July Fourth parades, she teaches seminars on health maintenance -- she's a former Army nurse -- and entertains at nearby nursing homes.

"She has a gift for it. She goes in there and brings 'em back to life, gets them singing and interested in life again. She works with the solitary residents committee too."

Rothchild himself, at 62 one of the youngest members of the Rossmoor Kiwanis Club, has organized a drive for a charity and educational foundation. He's getting involved in the ecumenical movement and has invited Christians to his Jewish temple.

"We came here with two sets of golf clubs," he says, "but we haven't played here once. We do play when we go off for vacation, but here we just don't have the time. I put in as many hours as I ever did, and I'm not making a dime, and I'm having the time of my life."

When they moved to the neat, compact bungalow (two bedroom suites, two baths) five years ago because they were tired of mowing a big lawn, they talked her father into moving in a few houses away. He died soon after, but her mother is still here and thriving.

"Singles have so much to do here," says Miriam Rothchild. "They can get around on the free bus and there's no worry about coming home alone. People here are so busy, what with community stuff, church, crafts, bridge or whatever, it's hard to fit the grandchildren in. So the children aren't going to be bugged by grandparents hanging around all the time."

Like most of the residents, she is a suburbanite, and as the mother of two daughters by an earlier marriage she is glad to have a grandson over for the night occasionally but isn't about to become swamped by child care again.

"I've been through that. I've done my time, been there. I don't want to have to worry about diaper service again."

Is there nothing she misses about the old life?

"My garden," she says, a bit wistfully. "You can't do vegetables here. And I had a big beautiful house with 10 rooms and lots of storage space and lovely gardens . . ."

But that's a problem faced by every older person moving into smaller quarters, in Rossmoor or anywhere.

Mid-afternoon at the clubhouse: In the main room, around a fountain, 20 people play bridge at folding tables. There is one mah-jongg table. Women play together, men play together. No mixed doubles. A few people lounge on sofas around the room, reading magazines or gazing at an exhibit of oil paintings by Mariano Eckert, instructor for the artists' guild. One white-haired man with a cane walks laboriously around the room twice and goes out.

Down the hall, past the travel office, art studio, education-recreation office and woodworking room, is the Ceramicrafters studio, where nine women and one man paint clay figurines made from molds. A half-dozen men play billiards in another room. The bulletin boards down the hall are crammed with notices: lawn bowling, chess, sewing, camera, duckpins, service clubs, Interfaith Chapel hours, anti-abortion fliers and political posters. A map lists bird sightings in the area.

Man to woman at the door: "You coming to the lunch? They got two kinds of chicken salad."

Woman to man: "No, I've got workshop today."

Not everyone is a dynamo, of course. In fact, the original proposal called for a hospital on the site, so that a resident could be hospitalized without ever leaving home, so to speak. This was felt by some to be bad for the town's image and was opposed by the Montgomery County Medical Society, too. There is, however, discussion of a "life care" center, perhaps to be built over the proposed shopping center at the Rossmoor gate.

All incoming residents are urged to fill out a medical questionnaire for the files of the existing medical center, by the way.

"Two husbands died in our building this year," says Marion Baldwin, a six-year veteran here living in a ground-floor apartment. "Some people feel a life-care center would give us an old-age image, but some feel it's necessary, after all."

Very active herself -- a retired public relations executive, she's hostess at the Cascade restaurant part time -- Baldwin has been especially concerned about the elderly residents of Rossmoor, a name she prefers to Leisure World.

"I know all the singles on the first floor here," she adds. "I see them every couple of days, and we try to get the old ones to have a phone companion, someone who checks in with them daily."

One project that she has promoted as president of the Ki-Wives is the Vial of Life program: A red dot pasted to the refrigerator door indicates that whatever medicines the resident needs are inside, along with instructions. This is for the rescue squad that may be called to the apartment and have to cope with an unconscious person whose history they don't know.

It's not just the busy people who enjoy this life, Baldwin says. A war widow with two children, she knew all about loneliness, "those long, long holidays," and many a time she would have appreciated the cozy small-town atmosphere of Rossmoor, where if you hear a noise outside at night you can just pick up a phone and bring out the guards.

"Most of us are here for the security, the serenity, just the good vibes. When I remarried, we lived at first on the 20th floor of an apartment tower near here. I hated it. So many transients. Those empty corridors. So we came here."

Her husband, Leo, travels now and then for the American Association of Retired Persons, but she meets lots of people at the Marriott-run restaurant, and keeps track of them.

In all her broad contacts, she has met maybe a dozen people who didn't like Rossmoor, "and they were the newly widowed ones who'd had large homes and were dumped here by their kids." Content today with her neat apartment and the bric-a-brac, the garden, the bicycles that she and her husband like to ride, she never wants to leave.

"You fall in love with it. Some people think we're fenced in, cloistered, and we are. But the amount of interest and effort we put in to support this type of thing makes it go."

The reason Rossmoor works for its residents is the homogeneity of its people.

Of course there are differences. There is the running debate over medical facilities. Recently, the high-rise issue broke up bridge games and golfing foursomes, because The Greens will double the population. It is expected, however, to bring in more young people -- that is, in their fifties -- and most everyone seems to agree this is a good idea. Also, the project will include another clubhouse, with an indoor pool at last, another restaurant, a theater, tennis courts and a shopping mall.

Some residents still were unhappy with the whole thing. But when the developers offered two separate plans for their land, one solidly built up with three-story buildings and one with high-rises and open space between, the mutuals voted unanimously for the latter, and so did the county planning board. For economic reasons, it was impossible to leave the land vacant.

"These people have many things in common," observes Giuseppe Cecchi, president and founder of IDI, which developed the Watergate and several area high-rise complexes. "They are upper-middle, they are comfortably off, they value the security, the secluded residential community with a strong identity, the resort atmosphere. They like being able to live a Florida life style and still be near their children. And half of them paid cash."

Ironically, these apartments and Rossmoor in general are beginning to sound like a return to the old-fashioned extended family that the suburbs helped to break up in the first place. Many buyers are bringing their aged parents to live next door or down the hall. One family of parents and married children has arranged a double unit with separate sleeping and dining quarters but a common living room.

A survey by IDI that drew 949 responses -- 42 from people under 60, 360 from the 60-to-70 group, 547 from those over 70--found considerable uniformity of taste. Nearly everybody watches "M*A*S*H." Otherwise, the main interest is in the news, movies and sports events. Older people watch more prime-time shows on weekends, again with emphasis on what we used to call current events: "60 Minutes," "Meet the Press," "Face the Nation," "Agronsky & Co."

The overwhelming magazine favorite is Reader's Digest, with Smithsonian a distant second, and after that Modern Maturity, National Geographic and Changing Times.

Notes Leo Baldwin, who works among the retired: "These are mostly successful people, with high-level socializing skills. They're not reclusive or exclusive. Most were high achievers on the job, so they get heavily involved in activities here. There are scattered cases, of course, of people who have suffered losses, sickness, whatever, and you don't see them out and around as much. But there probably aren't many. The same as anywhere."

There are only a few dozen blacks, Orientals or other minority races, according to manager Sullivan's office, which does not keep track of this statistic.

The Katzes live in Silver Spring but have bought a unit in The Greens, hoping to move in next year. They are buying an apartment near her parents.

Jay Katz sold his Virginia grocery store when he developed hip trouble and had knee surgery. He's not so sure he wants to move.

"I'm the one who wants it," says Connie Katz. "If he needs an operation and has to go to the hospital, I'm not staying in this house overnight. It'd make me nervous."

"I don't know," he mutters. "I've been meaning to start playing golf . . ."

Replies Connie Katz: "But all the activities at Leisure World! And the amenities, and there'll be a pool. And we can ride bikes!"

"I'm not riding a bike here."

Connie admits that he is not handy around the house, that he doesn't like to build things or putter in the garden. "But we'll have a bigger bedroom and two separate baths," she adds, undaunted. "I've been dying to put a chair in the bedroom for years!"

"I don't know," murmurs Jay Katz.

But he'll go.

From Mutual World News, Rossmoor's newspaper:

"NEWCOMERS COFFEE . . . The Welcoming Committee of the Education & Recreation Department invites all newcomers of the Leisure World Community to attend a Coffee Hour in the Clubhouse. If you have been a Leisure World resident, newly arrived since April, or if you have been unable to attend one of these enjoyable and informative events during the year, you are cordially invited . . ."