Change comes slowly to the proud, turn-of-the-century Ontario apartments, one of the city's grande dames of architecture and tradition. Shaded by tall oaks, guarded by granite gateposts and by the ghosts of its former guests - General Douglas MacArthur, Admiral Dewey, Woodrow Wilson - The Ontario hunkers down like a giant, six-story Buddha.

Once an exclusive summer retreat for wealthy Washingtonians - who then lived three miles away - the Ontario was overtaken by the city but never overwhelmed. It has weathered the rise and fall of neighborhoods and presidents, outlived the rites of calling cards and doormen and marched stoicly toward the pointed fingers of the egalitarian age. Like the city around it, in the last 10 years it has become modestly heterogeneous in age, race and economic condition.

Yet, the Ontario endures, a stodgy haven for aristocratic values, just three blocks from the Latin rhythms of Columbia Road and the ethnic gumbo of lower-income blacks, whites and Hispanics who boogie together inside Smallwood's Launderama.

"When you move into The Ontario, you become 'an Ontarian,'" says former resident Peter Colasante, 31, Calvert Gallery owner. "Everyone used to retire to their apartments late at night, pour drinks and worry how the world was crumbling around them - how The Ontario was the last bastion and refuge against the world."

"This is no groovy place - not yet," says Mary Lemp, a trim, sixtyish widow who moved there in the 1950s with her husband, a distinguished Army Colonel. The colonel and Mrs. Lemp hung old masters on the walls, set gleaming silver on the Louis XV buffet and fought with like-minded residents to preserve the Ontario as a fortress of quiet elegance in an age of declining standards.

Some residents say life at 2853 Ontario Road NW reminds them of small-town life - rife with back porch political intrigue and populated by busybodies who make it their business to know everyone else's. It takes about 15 minutes for Ontario "spies" to report illegal dog droppings or $35 parking infractions, says one long-time resident - "We've got a pretty good underground."

Sunbathing on the front lawn is forbidden, and burning wood in your fireplace on a cold winter night could bring a $500 fine. Dogs may roam on leash only, and overnight guests staying longer than two days are required to fill out a card. It's all in the 32-page rule book.

"At The Ontario, everyone goes by the rules," says Allan Angerio, 35, a Georgetown University biology professor and the ever-natty board president who stalks the terrazzo floors in his soft Italian leather shoes. "There's no special treatment."

The Ontario has always been known for its characters - and its character. The place has 10-foot ceilings, polished brass mailboxes, halls like bowling alleys and wrought-iron balconies.

Once, say residents, an heiress got so angry at her husband that she leaped off her fifth floor balcony, landed in a peach tree and walked away without a scratch.

Gen. Douglas MacArthur lived in the building, as did his mother. She built a special staircase outside her apartment to avoid the hoi polloi on her way to the now-defunct basement dining room.

Woodrow Wilson, says one resident, courted his second wife there. Other Ontario alumni include author Pearl Buck, two retired nurses who claim to have chased ambulances with Hemingway in Spain and a divorced Hollywood screen-writer who was kicked out after chasing his mother down the hall with a butcher knife.

Such are the legends on which The Ontario is built.

Constructed on the old McLachlin estate at the turn of the century, the Ontario was touted to the wealthy through ads glorifying the cool, healthful breezes blowing up from Rock Creek. When no one came, developers pulled strings, persuading city officials to extend trolley tracks into the building, and Capitol Hill ladies in long gowns and their men in formal dress rode out to take dinner.

It became home for senators and congressmen, whose wives retired to the roof to smoke and play poker beneath the white cupola.

"It used to be THE place to live," sighs, Lemp, offering a sherry. "Everyone had maids and chauffeurs and butlers. The people next door had velvet drapes and lace curtains. Oriental rugs were everywhere."

Residents rarely left the building except "feet first," says Clarence Streit, 83, a retired foreign correspondent. Married 58 years, Streit and his French-born wife, Jeanne, residents since 1941, can see the Washington Cathedral from their fifth-floor balcony and hear the lions roar at the zoo. In his prime, Streit covered the Greco-Turkish War, Mussolini's climb to power and wrote "Union Now," a World War II bestseller that urged democratic nations to bind together in a political federation as the solution to world peace.

Residents snapped up apartments for a song when the place was converted to a cooperative in 1953, but some left in the general middle-class exodus from the city that followed the 1968 riots. Ten years ago, attorney Kevin Tighe, 35, paid an "astronomical" $14,500 for a one-bedroom apartment. "I knew I'd paid too much when the seller broke into tears and said, 'Oh, thank you! Thank you! I never thought I'd sell it.' I could have bought it for $9,000."

His present four-bedroom luxury apartment with three fireplaces and a sauna just went on the market for $270,000.

Ownership at the Ontario, however, demands government participation required of any privileged citizen in a class-dominated democracy. Caring passionately about the decor is nothing less than noblesse oblige.

It took nearly two years of bitter wrangling to agree on a color to paint the halls. It took almost eight anguished years to chop down a tree.

At The Ontario, a home for shepherds in an era of sheep, everyone has an opinion. "We have 116 owners and sometimes, 116 different views." says resident Chris Camp, a Bette Davis look-alike and Ontario officer. "A sociologist would have a field day if he came here and spent a month."

"We're cooperative only in the legal sense of the word," resident Mildred Pappas said.

On the other hand, Ontarians tend to the infirmities of their neighbors, taking turns cooking when a resident is sick, offering comfort in times of sorrow.Nor do they miss a chance, in better times, to drink a toast.

Indeed, so strong is the tie that binds that neighbors have frequently rescued fellow residents. A 49-year-old Northwest Washington antique dealer was found beaten to death in his apartment last summer, and residents said they previously untied him from the bonds of homosexual lovers he'd brought home to The Ontario.

In the wake of the still-unsolved murder, some residents say they were pressured into taking a pledge of silence in the face of questions from outsiders, lest the news besmirch The Ontario's reputation.

"Everybody may know everybody else's business, but if anyone gets into a jam, we take care of them," says Florence Swift, 65, a retired credit union treasurer.

"Apathy is a problem in a lot of our buildings, but The Ontario has never suffered from it, said property manager G. Paull T. Sargent II, a portly, thirty-fivish gentleman who drew deeply on a filter tip, the pride in his voice as polished as the Guccis on his feet.

In one of the common clashes of culture and taste that began flaring in the sixties when young, upwardly mobile professionals began buying then-bargain apartments in the elderly enclave, several residents took offense last summer at a new resident. He had set up a card table on the front lawn, peeled off his shirt and started to type.

"Sunbathing out front just wouldn't be appropriate," sniffs Lemp.

And so the newcomer, Watergate journalist Carl Bernstein - who grew up in the neighborhood and once delivered pressed tuxedos to the building with his grandfather, a dry cleaner - put on his shirt.

Bernstein denies being cowed by little old ladies.

But they can be tough, as one elderly resident demonstrated when she took to carrying a brick in her pocket-book as a defense against muggers. Accosted at the gates, witnesses say, she swung the purse like a bolo, missing the attacker and knocking herself down - and out. Apparently fearing a heart attack, the man dropped his gun and ran.

Keeping the peace at The Ontario falls to Claudia Owen, a hardboiled, chain-smoking Arkansan with a twinkle in her eye. Some profess affection for the silver-haired resident manager of 10 years. Others say she strikes terror by her very presence.

"All my life, I've been told people were intimidated by me," the former Air Force bookkepper said laughing. "Once, at a dance in Iceland, an officer said, "I'd ask you to dance, but I can't stand intelligent-looking women."

A seven-member elected board governs the co-op and doles out the $250,000 annual budget, some say with an iron fist. But at a recent quarterly meeting, 50 residents voted to table a motion to refurbish the Green Room - even though the president pleaded embarrassment at having to interview Sen. Bill Bradley (D-N.J.), who was seeking entree to the building, in shabby surroundings.

"The management is like Mussolini. You may not love them, but they make the trains run on time," says resident George Burch, 42, a management consultant who parks his black 1965 Cadillac Fleetwood out front and a blue 1963 Maserati out back.

"Once you live in The Ontario, you understand why there's an adversary relationship between the mayor and the city council, the president and Congress, Egypt and Israel," says Camp.

In one bloody political coup, long-time owners managed to slap a 15 percent maintenance fee surcharge on residents who would lease their apartments. Fewer resident owners, they reasoned, would mean fewer volunteers for the countless committees that provide slave labor.

Kay Frederic, a short, plump woman with orange hair and a reputation as a whiney gadfly, heads the History Committee. Residents wonder what she's learned during years of research - but she's not telling.

A Pigeon Committee once solved the bird dropping dilemma by setting traps and relocating kidnaped pigeons to the countryside.

Residents even have their own newspaper, The Ontario Bulletin, a chatty, bimonthly newsletter that chronicles local events from the trivial to the cosmic. On Aug. 27, 1976, when the towering, 125-year-old red oak beside the summerhouse was chopped down, The Bulletin was hot on the story.

For eight years, residents had debated to chop or not to chop. The oak was treated and trimmed, fertilized and fed intravenously. Nothing worked. The High Tree Subcommittee adopted a "wait and see" policy. They were overruled by the board.

Finally, a tree doctor certified the condition as "dangerous." Down it went. "Sometimes we sacrifice for a greater good - and this is wisdom," wrote editor Mildred Pappas.

Mourners wore green. CAPTION: Picture 1, The facade of The Ontario reflects its turn-of-the-century elegance.; Picture 2, "At The Ontario, everyone goes by the rules. There's no special treatment." - Board President Allan Angerio; Picture 3, Claudia Owen, resident manager, stands in lobby of The Ontario.; Picture 4, Jeanne and Clarence Streit pose in their apartment. By Lucian Perkins, The Washington Post; Picture 5, Allan Angerio, a biology professor at Georgetown University, is present of the board of The Ontario. By Lucian Perkins - The Washington Post