Quiet St. John's girds for a boom

William J. Taylor remembers when serious crime was just a quirk occurrence here. Peering out from behind half glasses, the affable detective with the Royal Newfoundland Constabulary tells the story of a bank holdup that occurred in the late 1960s.

In true Butch Cassidy fashion, the robber strode into the bank, flashed his gun, and demanded money. But the teller just laughed. She thought it was a joke; no one robs banks in Newfoundland. It took a shot pumped into the ceiling to convince her otherwise.

Mr. Taylor and a number of residents think there is a moral here: sleepy St. John's is no longer quite so sleepy. While far from suffering from urban problems, this isolated seaport is being bumped further into the 20th century - squirming most of the way.

''It has always been a quiet, reserved type of town,'' Taylor says. ''Now you've got people buzzing around in $80,000 and $90,000 cars. You're dealing with a different type of people. If the oil boom ever hits, years down the road there is going to be more money coming through, more bars, and more drugs.''

Already St. John's wears two looks - one a timeworn port city harboring a centuries-old seafaring tradition, the other a growing commercial and energy-servicing hub. Perched on the tip of eastern Canada, St. John's is teetering uneasily between old and new.

This city of flat-roofed clapboard houses and rabbit-warren streets has become one of the world's most visible examples of a city struggling to cope with an impending ''petro boom.''

Snug in its rock-walled harbor, it has been an isolated hideaway for explorers, mariners, and fishermen for centuries. But in recent years it has grown as a commercial center as well.

''Newfoundland was always this poky little place out on the edge of Canada,'' says Mark Shrimpton, St. John's research director and economic development officer.

Things have changed, however, particularly since a consortium of oil companies announced a big offshore strike in late 1979. The scent of petro-bucks drew people the way catnip draws cats. Texas accents drifted through the airport lobby. Hotel rooms were booked solid. Ethnic restaurants opened overnight. And people bid high prices for houses.

Today the frenzy has died down. High interest rates and teeth-gnashing uncertainty over Canada's year-old national energy plan have prompted many oil companies to scale down their exploration off Newfoundland. What's more, the economy has bogged down.

The pause has given residents time to take a reflective glance in the mirror. Some don't like what they're seeing. Warm but stubbornly independent, many Newfoundlanders want to preserve their heritage and think quiet St. John's, with its Gothic churches and confectionery shops, is fine the way it is.

Worrying about the prospect of an oil boom, Douglas O'Leary, a beefy cabdriver, says in a thick brogue: ''You're going to get more crooks. A few years ago, you could leave your door unlocked.'' For protection, he carries a lug wrench in his car.

Bill Morgan has his worries, too. The bushy-browed crab fishermen, skipper of the 65-foot Eastern Princess, thinks the city's skyline is getting too big for its buildings. ''The oil development is going to make this place look more like New York,'' he says.

Yet St. John's will be getting bigger even without the energy-related developments. Over the last three decades a high birthrate and rural-to-urban migration have made it the fastest-growing city in eastern Canada. By 1990, the city's population is projected to jump 30,000, to 185,000.

Along with the growth have come some of the fortunes of urban living. Many residents, for instance, now get the Toronto Globe and Mail. Some movies show up here before playing in the rest of Canada. And you can ''buy fresh bagels here now,'' one resident says.

But crime is no longer an oddity here, and police are preparing for what might lie ahead.

Still, some Newfoundlanders believe too much is made of the changes. They chafe at tradition-bound residents who want to spin the province into a cultural cocoon. A little wealth with a few social tural changes is much better than a depressed economy, they argue. Besides, it isn't all Texas oilmen under those cowboy hats in town.

''There are lots of cowboy hats and boots around - but that's a North American phenomenon,'' says a corporate official. ''Who's to say it's oilmen?''