MONTREAL - With nearly 400 years of settlement that have left a legacy in every corner, a countryside stunning both in its beauty and its variety, and a cultural flavor unlike anything anywhere, Quebec should be swamped with tourists.

Instead, Quebeckers are becoming increasingly aware that, although world tourist revenues are growing steadily, Quebec's share is not. And there is a lot of soul-searching under way here to find out why.

Industry experts and the provincial tourism department are particularly struck by the drop in the number of American visitors - long a staple of the Quebec tourist scene and the province's biggest market.

In 1973, for example, 4 million Americans crossed their northern border into "la belle province." By 1977, a full million fewer U.S. tourists found Quebec worth a visit. The same year, Quebec's travel deficit with the United States hit $206 million (Canadian), or about $45 a head.

Mind you, government tourism people will tell you that Canada as a whole has a deficit with the United States of more than $70 a person. But they don't smile much when they say it, especially since rising incomes here mean more and more Quebeckers have decided they can't get through the winter without that stretch in the Florida sun.

Since tourism is one of Quebec's major industries, hovering around the $1 billion mark, any drop in revenues has widespread consequences in jobs and investment.

The bad years started in the summer of 1975, and accelerated with the election of the separatist Parti Quebecois Government of Rene Levesque in November 1976. Naturally, in the industry at least, the government gets most of the blame for having scared off visitors from the United States and from the rest of Canada.

Certainly, American apprehension must have been heightened by the wondrously strange reports that began appearing in some U.S. publications when the world briefly turned its attention to the place where people democratically elected a government pledged to break up a country. All the prophets of doom to the contrary, though, there has been no fighting in the streets, and no need for the army to send out the troops to protect one faction from another. Neither event is expected.

Despite the fervor with which Quebeckers and other Canadians on each side of the national unity argument hold their views, the battles, though heated, are verbal.

But although government politicians often point out that Americans go lots of places where English is not the local language, there is no doubt that Bill 101, Quebec's language law, has made Quebec appear less attractive to some. Even on this score, the misconceptions in many American minds seem to outweigh reality.

There are, for example, no language police in smart new uniforms lying in wait throughout the countryside eager for the chance to carry off someome for speaking English. French is now by law the only official language of Quebec, but it is not the only language Quebeckers speak. There are still, as there have always been, thousands of English Quebeckers who spend days to end without either hearing or using a word of French. Sad, perhaps, but true and perfectly legal.

In major centers, and even many smaller ones, all the services that any tourist could normally want are available in English. Guides speak English, so do policemen, bus and taxi drivers, hotel and store clerks and waiters. Most restaurant means are bilingual.

In Montreal, Quebec City, Sherbrooke and many other communities, there are English language hospitals. And where there aren't, most doctors speak at least some English, because even if they took their training in French, many of their textbooks were in English.

However, in one very definite way, Bill 101 has changed the face of Quebec. English is now illegal on most commercial outdoor and traffic signs. There is still a lot of English to be seen, though, especially in Montreal and predominantly English-speaking areas in the Eastern Townships and communities close to the U.S. and Ontario borders. But, as the various deadlines set in the law take effect, notices in shop windows and other public places will become French only.

Tourist operators say the disappearance of English, especially on traffic and road signs, will be a big factor in deterring the visiting motorist from touring Quebec. Supporters of the law say a lack of English signs hasn't stopped Americans and English Canadians from renting cars and driving all over Europe.

It's no secret that rising gasoline prices have already cut into the number of Americans who visit Quebec by car. Whether language problems, real or anticipated, will be another significant factor, only time will tell.

Although language is a closed subject with the present government, every other aspect of the tourist industry has been under the microscope. A three-day so-called "mini-summit" with government, business and labor representatives held last fall concluded that the province is losing to appeal for two basic reasons: high costs and a fuzzy image.

Even with the substantial depreciation of the Canadian dollar (currently worth about 87 cents U.S.), everyone realizes that most Americans find traveling in Canada, and in Quebec especially, an unwelcome shock to the pocketbook.

Ironically, they also realize many Americans are not yet aware their money goes farther here now than it used to when the Canadian dollar was at par or a premium. Nevertheless, the highest minimum wage in North America, higher taxes than elsewhere in Canada, including an 8 percent sales tax on most items, can make Quebec a pretty pricey place. Shoppers should note, though, that the sales tax on clothing, shoes, leather goods and textiles has been abolished.

First-class hotel rooms in Montreal and Quebec run between $45 and $75 per person, double occupancy, depending on extras, with suites starting at $150 (Canadian dollars). Lesser quality accommodation is cheaper, of course. In Quebec City, in particular, there are a large number of small tourist hotels where rates start about $20. (Visitors are wise to change their money in banks to avoid service charges.)

And in the nooks and crannies of the province, there are camping areas, farms that take in visitors, and what the government calls Vacances-Families (family vacation plans) in which different kinds of approved efficiency accommodation are available. Rates vary depending on conveniences and regions. Provincial and national parks offer both scenic beauty and supervised facilities.

Costs asides, Quebec must still find the right way to merchandise its special flavor - the uniqueness it must first define. Europeans tend to see Quebec as North America with a French accent; Americans, on the other hand, often look for France with North American plumbing.

Quebec is perhaps a little of both and at the same time, neither. Four centuries of European settlers - first French, then English and now newcomers from all corners of the globe - have created here an atmosphere and way of life that exists nowhere else.

Montreal, where about 40 percent of the population is Anglophone, is a sophisticated, cosmopolitan, bilingual city. Despite all the helter-skelter demolition of modern years, it's a delightful mixture of the old and the very last-minute.

Quebec City is the provincial capital and the spot many consider the birthplace of Canada, and here people are almost entirely French-speaking. In North America's only walled city, the early beginnings still overshadow the recent outcroppings of glass and concrete. In both places, incidentally, good dining is considered a necessity of life.

Beyong these two poles of attraction, there is immense variety. First, there is the mighty waterway of the St. Lawrence, along whose banks the first French farmers set down their fields in horizontal strips and built their towns in the shelter of an enormous wooden cross.

On the south shore of the river, gentle rolling countryside leads to the fishing villages of the Gaspe Peninsula. Jacques Cartier claimed Canada here for the King of France in 1534 and Premier Rene Levesque was born here about 390 years later.

On the north shore of the St. Lawrence, farther west, the Saguenay River with its flordic cliffs flows up into the Lac St. Jean area. At its mouth, Visitors come every summer to catch a glimpse of the nine different species of whales spotted in the Saguanay and lower St. Lawrence - including the blue, sperm and humpback.

Farther west, about an hour north of Montreal, the hills start to rise into the Laurentian Mountains. Here, thousands of lakes and a whole host of resorts huddle among some of the oldest geological formatlons in Canada. The mountains, only 960 meters at the peak, look as if they've been rounded down by some giant mason with his grinding wheel.

South of Montreal across the river, heading toward the New York border, town names become English, although in the Eastern Townships most of the population no longer is. Still a substantial English community flourishes and in the summer, crafts and English language theater are major attractions.

Each region has its own customs, its own cuisine, sometimes its own music and its own language. Each adds something different to the special taste of Quebec.

Finding a common label is a problem to bedevil the tourist promotion experts. It's also one reason we say in Canada, "Quebec, ce n'est pas une province comme les autres" - Quebec is not a province like the others.