It looks like a big chunk of the German Ruhr that was somehow torn out of its natural surroundings and dumped in the arid Mexican desert 150 miles south of the Texas border.

Monterrey has none of the exotic charm that tourists associate with most provincial Mexican cities: It is all smokestacks and furnaces weaving a wreath of acrid smoke around a central core of glass-and-concrete office towers.

What Monterrey lacks in grace it makes up for in power and vitality. This city of 1.7 million is an industrial powerhouse whose importance to the Mexican economy is only slightly out-ranked by Mexico City, which has a population almost six times as large.

It is also the home ground of what everyone in Mexico calls the Monterrey Group, a shadowy collection of about 200 wealthy and conservative businessmen - most of them related to each other - who dominate the city and its industries.

The Monterrey Group has an importance that transcends its obvious impact on the economy. When it wants to, it can form what is, in effect, the only significant opposition in this country to the government.

That was the case during the just-completed six-year term of President Luis Echeverria. Many political analysts here contend that part of the turmoil and atmosphere of crisis that swept Mexico during Echeverria's final days in office stemmed directly from the animosities and feuding between the president and the Monterrey Group.

Similarly, these same analysts attribute much of the relative calm since then to the truce between the Monterrey Group and the new president, Jose Lopez Portillo, who was inaugurated Dec. 1. A few days ago, when Mexican newspapers reported that the Monterrey Group had "pledged its support" to Lopez Portillo, it was the subject of banner headlines.

The headlines reflected a belief, widely held in government circles, that Monterrey is the nerve center from which the group influences moneyed classes throughout Mexico, to oppose or support the government.

This is denied by Jorge Chapa, a supermarket magnate who is president of the Monterrey Chamber of Commerce. He says: "We are independent people - not lackeys of the government - and we have no hesitation about speaking out when the government pursues bad policies. But its ridiculous to say that we're at the center of a national conspiracy. We're too busy running our own affairs."

Eduardo Hoverman, director of the Industrial Employers' Association, does say, however, that Monterrey's business success offers "an alternative model" for the way Mexico should go.

"We are successful here," he says. "People here have the highest wages, the best benefits and social services in all Mexico. And it's been done by private enterprise - not by government controls and meddling. Our success is a reproach to the bureaucrats in the capital, and that is why they think of us as some kind of organized opposition."

The Monterrey Group's unusual role results from the fact that Mexico is, for all practical purposes, a one-party state. Every facet of the political system from the presidency down through the tiniest town hall is controlled by the Institutional Revolutionary Party.

Born out of the bloodbath of the Mexican revolution, the party is an umbrella organization that includes all the country's major politicians from the right to the non-Marxist left. It tolerates the existence of other parties without allowing them any power, and it maintains its monolithic control over the electorate through three party "sectors": labor, farm and popular.

Although all of the party's leaders pay scrupulou slip-service to the radical ideals of the revolution, the party has actually been led throughout most of the postwar period by conservatives. Over 24 years, Mexico had four successive presidents who believed that the solution to the country's problems lay in rapid industrialization, who emphasized incentives for local and foreign investment and who maintained generally good relations with business forces such as the Monterrey Group.

That changed dramatically when Echeverria became president. He began not just to preach radical rhetoric, but to make some moves toward practicing radicalism as well. He sought to align Mexico with the attitudes of the Third World, to bring about a far greater redistribution of income and to increase government intervention in the economy through heavy spending on public works and basic industries.

Inevitably, this caused alarm in the business community and led to growing tension with the government. Since much of big business in Mexico is tied to American and other multinational companies that like to keep a low profile, the most visible aspect of the rift between Echeverria and the industrial complex came to center on the Monterrey Group.

It is a strictly home-grown group whose influences in Mexican affairs is analagous to that once wielded in Germany by the coal and steel barons of the Ruhr. Just as the Ruhr once was synonmous with the names of Krupp and Thyssen, the Monterrey Group also boasts two names - Garza and Sada - that spell power.

The story began in 1890 when Issac Garza and Franciso Sada founded the Cuauhtemoc brewery in what was then little more than a desert outpost. The brewery is still a major element in Monterrey business, producing the Bohemia and Carta Blanca brands so well-known to beer lovers.

It also provided the springboard from which the two founders, in conjunction with their myriad relatives and descendants, launched a vast series of enterprises that included glassmaking, tinplating, paper manufacturing and banking.

Together, these enterprises form the Monterrey Group. They provided the nucleus for an industrial expansion that now sees the Monterrey area, with only 1.5 per cent of Mexico's population, account for 7 per cent of the country's gross national product. In manufacturing alone, Monterrey contributes 24 per cent of national industrial production.

The group, and the other local industrialists who followed its lead, prospered by hard work and initiative, by resisting takeovers from outside through the development of their own technology and by innovation in employee relations.

For decades, the development of the group's enterprises into a billion-dollar operation was dominated by Issac Garza's son, Eugenio Garza Sada. In 1973, Garza Sada, then 81, was murdered by leftist guerrillas in an abortive kidnap attempt.

Much of the group's hostility toward Echeverroa stems from the killing. Its members blamed their patriarch's death on what they considered Echeverria's inflammatory anti-business rhetoric and softness toward radical groups.

Partly as the result of power struggles following Garza Sada's death, the group has subdivided into three distinct, but interrelated holding companies. Family connections remain intact.

A factor unitedg the various segments of the group has been unrelenting hostility toward Echeverria and his policies. Its members charge that his anti-business talk and his heavy spending in the face of the world recession are the principal causes of Mexico's current serious economic problems.

The inevitable result, they contend, was the inflation and adverse balance of payments that put the peso under heavy pressure, resulting it its devaluation after years of stability.

On the other side, Echeverria's supporters charge that the Monterrey group sent enormous sums out of the country and was responsible for a whispering campaign that Echeverria was planning a coup to keep office.

Many observers think that Echeverria's last major act in office - the controversial expropriation of more than a quarter-million acres of privately owned farmland in northwestern Mexico - was intended, in part, as what one calls "a symbolic last twist of the knife into the Monterrey group and its allies."

Although the land seizures caused great outrage here, Monterrey's industrial leaders have been calmed down considerably by Lopez Portillo's tendency to talk softly and plead for confidence from business. The general feeling here is that the new president, who formerly served as finance minister, will quietly lead the government and the party back to cooperation with the industrialists.

Eduardo Hoverman sums up the dominant feeling here: "We are a poor country with a growing population, and to make any kind of advance, we must have economic growth. If the private sector doesn't have confidence in the government, it's not going to invest, and there will be no growth. Lopez Portillo know that, and he knows there's no way he can get around that fact. It's as simple as that."