The first satellite pictures of what the massive Mexican earthquake had done to his home town hit Salvador Uribe, a 4-year resident of Los Angeles, squarely in his gut. That hospital with floor squashed upon floor was where his father, a surgeon, worked. "I felt like I was about to fall over," he said.

In the overcrowded duplexes of east Los Angeles, as well as the tidy bungalows of Phoenix and many spacious mansions in Houston, residents of the American Southwest with relatives in Mexico watched the videotapes on Spanish-language channels last week in shock.

The immediate outpouring of emotion, fund-raising and ingenious communication schemes left little doubt about how much Mexico has remained, and in some ways grown, as an influence over the regional psyche.

This is nowhere more evident than in southern California, where the 2 million-member Mexican-American community is the largest in the United States.

Los Angeles' annual Street Scene Festival, in which much of downtown becomes a walking mall of shops and entertainment, has been turned this weekend into a 12-hour televised fund-raiser to be shown by SIN, the U.S. Spanish-language television network, as well as by outlets in Latin America and Europe. The Los Angeles city schools, where half the students are Hispanic, have announced a $250,000 fund-raising campaign for quake victims.

The approximately 30 scheduled flights a day from Los Angeles to Mexico City have been loaded with Americans seeking to locate or help their Mexican relatives. With almost no direct telephone links to the shaken Mexican capital, Americans and Mexicans have devised a dozen ways to bridge the gap -- amateur radios, a space shuttle satellite and airline couriers who have brought a bit of the pony express to the jet age.

The Dallas Times Herald has been printing reports of the earthquake in English and Spanish to meet the enormous demand for news from the Hispanic community.

La Opinion, the Spanish-language daily here, printed a special weekend section of translated Los Angeles Times reports on the tragedy. Television correspondents from the English-language stations here and in other Southwest cities camped out at their Spanish-language competitors' studios to record the initial SIN (Spanish International Network) transmissions from Mexico showing earthquake damage. Local stations, both English and Spanish, throughout the Southwest dispatched correspondents to the scene, as did nearly every major newspaper in the area.

At the colorful Mexican consulate overlooking the little park that commemorates the first Mexican settlement here, Deputy Consul General Enrique Silva Guzman moved from telephone to telephone, trying to clear snags in an administrative machine that has been churning out passports to concerned relatives nearly 24 hours a day.

His boss, Ambassador Augustine Garcia-Lopez, has often spent the night in his office as the demands for information have escalated.

"Everyone is very concerned," Silva said. "So many people have relatives back in Mexico -- not just Mexico City but many of the little towns."

U.S. Border Patrol officials denied rumors that they anticipated a sudden surge of crossings into the United States by people impoverished by the earthquake.

"There has been no increase," said a U.S. Immigration and Naturalization Service spokesman. "We think people are so concerned with what is happening in their locality that they may put off any plans to come north." The spokesman said it is possible, however, that border traffic will jump in two or three months, when Mexicans who returned home to help relatives decide to try to enter the United States illegally a second time.

The consulate, helpless at first to gather much information from Mexico, managed on Monday, through the intervention of Hughes Communications, to set up a regular telephone link with the capital. The U.S. firm had built Mexico's Morelos communications satellite, launched from the space shuttle in June. At the consulate's request, Hughes sent an engineer to Mexico City to install equipment for a temporary hookup, now used to transmit Mexican families' messages assuring American relatives they are safe.

Ben Pesta, associate publisher of Muscle & Fitness magazine here, found himself last week enlisted at the beginning of a makeshift communication network with a 19th Century flavor.

Waiting at the Mexico City airport for a plane home a few hours after the earthquake, he was approached by a young woman with several pieces of lined paper in her hand. "Please," she said, "en Los Angeles, mi familia . . . this man is the . . . brother of my . . . mother?"

Not sure of his Spanish, Pesta said he nevertheless understood that she wanted to get a message out. By the time his plane left, he had a pocketful of similar messages. After midnight he found himself making calls from his home to people all over the area. "You are an angel," an elderly woman told him.

The system has since become more sophisticated. Western Airlines has prepared printed forms that relatives fill out at Benito Juarez International Airport in Mexico City. They go out on the next flight, and Western employes in Los Angeles phone the messages to U.S. relatives.

Salvador Uribe was lucky. He only had to wait four days for word that his father has narrowly escaped the hospital collapse. Dr. Uribe's message was among the first to arrive at the consulate over the new satellite line.

"He said he had had surgery from 5 to 7 a.m., then he decided to go across the street for a cup of coffee," said Uribe, who works as an administrative assistant at the consulate. "While he was sitting there sipping, the quake hit and the whole thing came down."