WHEN Lupita Jones, a beauty from this dusty metropolis, won the Miss Universe pageant last month, a Mexican newspaper identified her proudly as a Tijuanense.Such is the rancho grande image of Mexicali, grouses a local resident, that in the national conscience the city is a satellite of the glittery border giant Tijuana, instead of a city in its own right, and the capital of the maverick state of Baja California to boot. Geographic isolation - bounded by a restricted international border to the north, desert to the west, and the Sea of Cortez to the south - has helped shape Mexicali's feisty character of upstart politicians, big ranchers, businessmen, and a broad working class. While many border cities have huge transient and poor populations either headed toward jobs north of the border or languishing in urban slums, Mexicali has a stable population with few slums and a high standard of living for Mexico, says Arturo Ranfla, director of the Institute of Social Research at the Independent University of Baja California (UABC). Fewer people use this inland route to the border region, but those who do, and can stand the desert heat, tend to stay, he says. Baja California jolted the nation with its independence in the 1989 elections. Mexicali was the first state capital won by an opposition party since 1929 when the Independent Revolutionary Party began its exclusive hold on Mexican politics. That it was the free-market, business-oriented National Action Party that won said much about the United States influence on this border town. The standard of living here is high for Mexico because farm and factory salaries here, and just across the border, are considered high. "Mexicali is nothing but a rancho grande: It's not sophisticated, few places are open late. It's a rural community that has to work hard to keep its high standard of living, so it turns in early," says Reynaldo Ayala, director of the Institute for Border Studies at San Diego State University's Imperial Valley campus. The late-night dinners and evening promenades familiar throughout Latin America are replaced here by an early morning march to work. Each morning by 2, thousands of farmworkers can be seen making their way - legally and illegally - across the border to jobs in the US. The flow continues through the morning as thousands of other workers go to jobs as clerks and shopkeepers in regular 8-to-5 jobs on the US side. These US jobs pay in an hour what can be made in a day in Mexico. But vegetable-export farms, factories making everything from electronics to Taco Bell taco shells, and state and federal bureaucracies headquartered in the bustling and modern civic center here on the Mexican side draw many more workers than the US side does, says Javier Rivas, a farmer and industrial consultant who chairs the Mexicali Association of Maquiladoras (foreign-owned-and-operated assembly plants). Salaries here are high by Mexican standards, he says, noting that eight months ago local base wages increased from 90 cents an hour to between $1.40 and $1.70 an hour. The life in Mexicali has proved attractive enough to hold Rosa Isela Soto Camacho, for example, from going farther north into the US. She came from Sinaloa to the Robledo squatter settlement here eight years ago, and found enough work to forget making a desperate attempt to illegally enter the US. Mrs. Soto and her husband, who own their Robledo lot and house, are steadily employed, and have four children in school, exhibit a stability typical of Mexicali's broad middle- and lower-middle classes. The biggest complaint people like the Sotos have is that when the summer sun revs up, the cost of electricity to cool homes is too high. This beef regularly causes street demonstrations. That most people even have electricity is a measure of the relatively high standard of living. "Mexicalians feel secure about themselves, they don't feel poor, they feel more capable" than their counterparts in the interior of Mexico, says Nicole Diesbach, a UABC psychology researcher who has studied Baja Californians an d speaks of US-Mexico border populations as almost a third nationality. Baja California Secretary of Finance Eugenio Elorduy likens the maverick mentality of Baja Californians to the independence of pioneers of the US West. But he notes sharp resentment over border issues. Mr. Elorduy and others here echo nearly universal criticism of US immigration authorities as symbols of US arrogance. Mexicalians, from rich to poor, chafe at the treatment US Customs officials give them at the border. "Like we're criminals," says one businessman, who like many Mexicalians crosses frequent ly to buy groceries, clothes, and to use a post office box in Calexico because of the superior US postal system. While the US can restrict the flow of legal Mexican immigrants, it can't restrict the flow of the New River. One of the most polluted in North America, it winds through Mexicali, picking up toxic industrial and agricultural wastes and the sewage of nearly a million residents, and then flows thick with foam through the Imperial Valley into the Salton Sea. While government officials say they are doing all they can with tight budgets to solve the problem, some Mexicans feel much of the problem comes from the foreign countries that set up factories here. The responsibility, argues Rafael Martinez Retes, a prominent attorney and journalist here, still remains with Mexican authorities to demand high environmental standards of foreign industries and to tax them in order to fund compliance measures. But problems don't always flow from south to north, Mr. Martinez notes. The Imperial Valley signed a conservation deal with the Los Angeles Metropolitan Water District allowing the district to line the valley's dirt canals so that more water reaches Los Angeles. The virtues of the plan, he says, are clouded by the fact that it will reduce the amount of Mexicali Valley ground water.