MEXICALI, MEXICO -- While the visiting President Bush posed in a sombrero to celebrate Mexican-American friendship on Nov. 26, Eduardo Zamores, 15, lay half-conscious in his hospital bed suffering from a bloody lesson in the facts of life along a violent and often unfriendly border.

A U.S. Border Patrol agent shot Zamores in the torso with a 9mm Beretta pistol in the early hours of Nov. 18 as the youth scrambled atop the cyclone fence dividing Mexicali from Calexico, Calif. Zamores tumbled onto the Mexican side of the fence, seriously wounded by particles from a hollow-tipped round that damaged his liver, lungs, diaphragm, intestines and spleen.

The slight boy, who remains hospitalized here, has become a symbol of growing violence along the Mexican-American border that has enraged Mexican activists, frustrated the Mexican government and cast a shadow over rapidly improving relations between Washington and President Carlos Salinas de Gortari's reform-minded adminstration in Mexico City.

In the last year, according to U.S. and Mexican authorities, at least 15 Mexicans have been shot and killed along the border and several more severely wounded by gunfire in what authorities on both sides of the line view as a disturbing increase linked to the badlands atmosphere in an area overwhelmed by illegal immigration and drug trafficking.

Nine were killed by Mexican outlaws preying on illegal immigrants -- particularly in the San Diego area, where most illegal Mexicans slip across in search of higher-paying jobs in the United States. Mexican and U.S. police, in a display of cross-border cooperation, recently set up coordinated teams that have significantly reduced the incidence of such crimes over the last three months.

But U.S. Border Patrol agents also shot six Mexicans over the last year, killing four of them. Particularly worrisome for Mexican officials is that none of the agents involved has been prosecuted or even identified, despite what Mexican officials contend are clear indications some of the shootings were unjustified.

In addition to the Border Patrol shootings, one 12-year-old Mexican boy was shot and killed May 18 by a U.S. civilian firing from a border-side house. Another Mexican, a 24-year-old mason who authorities said was wielding a bricklayer's trowel, was shot and killed May 21 by a San Diego policeman. As with the shootings by Border Patrol agents, no charges have been filed in either case.

Roberto L. Martinez of the American Friends Service Committee's U.S.-Mexico Border Program said such incidents fit into an environment encouraged by extremist U.S. groups fighting what they say is an unacceptable influx of illegal Mexican workers. One group, Light Up the Border, has vowed to help the Border Patrol catch illegals by illuminating the frontier with automobile headlights.

Intolerance toward illegals and even shootings are not new. The Foreign Ministry has lodged 75 formal complaints over border shootings with the U.S. government since 1985. But U.S. and Mexican officials alike said the number of such cases has risen over the last two years. After declining in 1987-88, the number of illegal border crossings has shot back up to more than a million a year.

"This last {agricultural} season the violence increased a lot, and it worries us a lot," said Luis Wybo Alfaro, director general of the Mexican Foreign Ministry's border affairs department.

The string of shootings by U.S. authorities this year, combined with growing irritation about the lack of prosecutions, has generated concern in Mexican public opinion and, partly as a result, at the highest levels of the Mexican government. The Mexican Senate's human rights committee held hearings in Tijuana on the issue three weeks ago -- the day Zamores was shot -- and border-monitoring groups have scheduled a protest session with Salinas in the same border city on Monday.

"This is really the problem from the point of view of the Mexican government -- the impunity of Border Patrol agents," said Enrique Loaeza, the Mexican consul in San Diego.

Bush and Salinas, at the outcome of their friendly Nov. 26-27 meeting in Monterrey, for the first time took note of the border violence and ordered their subordinates to work on ways to bring it to a halt.

Wybo said the Salinas government has drawn up plans to combat the violent robberies of illegal immigrants by Mexican bandits, who some officials allege include local Mexican police. In return, Mexican officials have expressed a desire to see their U.S. counterparts find ways to reduce violence by Border Patrol agents and punish those who use excessive force.

"Not in the whole history of the situation has one person been condemned -- never, never. If one person were condemned, the U.S. government would be relieved of a big burden," declared a senior official in Mexico City.

Gene McNary, commissioner of the U.S. Immigration and Naturalization Service, which controls the Border Patrol, pledged last Wednesday in Washington to review agents' field tactics with a view to cutting down the violence. He said in a statement that the review "will begin immediately to determine what steps the INS can take to eliminate or dramatically reduce these incidents."

Gustavo de la Vina, chief patrol agent in the key San Diego border region, said that in the busy season his agents make between 1,800 and 2,000 detentions a day, meaning shooting victims constitute a tiny percentage of the overwhelming volume of would-be immigrants taken into custody. Policy is that agents draw their weapons only in case of danger to themselves, another officer or an innocent third party, he said.

"There have been incidents," he added in an interview at his headquarters on the border. "But when you put that against the total number of arrests, has there been total mayhem out there? I don't think so."

U.S. and Mexican border-monitoring activists and Mexican officials nevertheless have begun to question the need for some of the shootings and the sincerity of the U.S. justice system in investigating alleged wrongdoing by Border Patrol personnel.

A Border Patrol agent fired three shots into a stolen van early May 26 in the town of Chula Vista, for example, wounding a 16-year-old Mexican boy in the neck and jaw and a 24-year-old Salvadoran woman in the left shoulder. The Border Patrol explained later the agent fired because the van lurched forward after he stopped it.

The mason killed May 21, Jose Eleazar Lopez Ballardo, was shot eight times in the front of his body, Wybo said. The San Diego police department said its officer fired to defend himself from an attack with the trowel.

The Federal Bureau of Investigation is investigating both shootings, authorities said, but no charges have been filed.

The Zamores shooting here provoked the strongest outrage, however, leading Foreign Minister Fernando Solana to declare Tuesday that Mexico is considering a demand for extradition of the Border Patrol agent who pulled the trigger.

Perhaps the concern swelled so fast because the Mexicali crossing had been peaceful compared to the Tijuana-San Diego region. Perhaps it was because the youth had a reputation as a harmless worker, washing windshields on the border crossing point to help feed his mother and her seven children.

In any case, residents staged a protest Nov. 28 that closed the Mexicali-Calexico crossing for nine hours from the Mexican side. As a result, Mexican laborers were unable to report for picking duty on Imperial Valley farms and Mexican traders were unable to reach the weekly Calexico Swap Meet that U.S. merchants regard as a key market.

"What I want is for the guilty man to be punished," said the youth's mother, Gregoria Zamores, 37. "He should be punished, because he is responsible."

Zamores, his voice still weak, told a visitor to his hospital room that he climbed over the 12-foot fence and moved about 10 feet into U.S. territory to get a better look at a ruckus going on nearby. When he saw a Border Patrol vehicle pull up, Zamores said, he ran back to the fence and climbed to the top on his way back to Mexican soil.

"I only wanted to see what was happening over there, what the guys were doing," he said, adding later: "There wasn't time for anything. He just came and fired. He didn't say a word."

Calexico Police Chief Les Ginn, whose force has jurisdiction, said the confrontation erupted when several Mexican youths pelted another Border Patrol agent with rocks just inside the border. The agent who fired his weapon came into the fray later, Ginn said, and declared that he saw Zamores "had his arm cocked preparing to throw a rock down at the agent."