On this city's cable television service one morning this spring, CNN Headline News was about to broadcast a report about anonymous death threats against U.S. citizens visiting Tijuana. The picture was replaced suddenly by scrolled programming announcements, reverting back to Cable News Network after the item had concluded.

"I find it dismaying, but we have orders from the Interior Ministry to block out news about Mexico," said spokesman Adrian Fournier of the locally owned Cablevision S.A., responding to a query about the apparent censorship, an increasingly common response to the local transmission, in English, of U.S. television news coverage of Mexico.

A Mexican official, contending that the cable company cut into the broadcast without official prompting, said it had nonetheless "acted responsibly." An emotionally disturbed Mexico City viewer "might have gotten the idea that it would be a good thing to go out and kill North Americans," he suggested.

The expanding penetration of American television here has made U.S. network treatment of Mexico a new irritant to Mexican authorities, who appear increasingly concerned about the domestic and international impact of such accounts.

Interference with U.S. news programs was especially frequent earlier this year when Mexico's narcotics trade was under scrutiny, acknowledged Mexican officials, who said they have the legal obligation to block local broadcasting of what they view as hostile or distorted foreign news coverage.

"We get a lot of complaints from customers about these interruptions, and rightly so," Fournier said, complaining that the government "treats viewers as if we were mental midgets."

Carrying much U.S. network programming, Cablevision S.A. appeals to a relatively small but influential audience of Mexico City professionals who speak English. Students are urged to subscribe to the service by advertisements promising that Cablevision will "improve your English." Other cable customers are attracted simply by its superior reception, as channels also deliver standard Spanish-language Mexican fare.

Sources at Cablevision S.A. say it now reaches more than half a million viewers in Mexico City, an urban area with 15 million people. In addition to CNN, it carries the three major network morning and evening news shows, most of which were subject to at least occasional censorship during the height of the drug controversy in February and March.

Cablevision programming director Eduardo Gayou, in a telephone interview, disclaimed knowledge of Interior Ministry orders and said U.S. news show interruptions are due to "technical problems." He added, however, that Cablevision halted English-language transmissions in March of San Antonio, Tex., nightly news programs because Interior Ministry officials voiced objections to what he called their "Tex-Mex" approach to Mexico and Mexican culture.

Also discontinued were evening news shows from San Diego, Calif., that frequently featured critical coverage of events in Tijuana and elsewhere along the U.S.-Mexican border.

Interior Ministry officials denied that they have issued blanket instructions banning local broadcasting of U.S. television news about Mexico. They said they have expressed no opinion about the San Antonio and San Diego news shows.

Yet Mexican broadcasters are prohibited expressly from televising material considered defamatory toward Mexico, said the officials, who spoke on the condition that they not be named. Mexican television stations are advised further not to transmit criticism of Mexican government policies by officials of foreign governments, the officials said.

After the February abduction and murder of U.S. Drug Enforcement Administration agent Enrique Camarena Salazar, one high-ranking official said, U.S. news broadcasts frequently "attacked the Mexican government or contradicted our government's policy statements without any opportunity for a Mexican spokesmen to respond. For this to be broadcast inside Mexico is unacceptable."

Failure to screen out news reports about Mexico that the government deems inaccurate or derogatory has occasionally led authorities to levy a 50,000 peso (approximately $200) fine on Televisa, the monopoly commercial television network that is Cablevision's corporate parent, the official said.

Although the fine is small, "Televisa doesn't like to be at odds with the government," he said.

Privately owned and Latin America's largest television company, Televisa simultaneously broadcasts on four channels, two with national audiences. Televisa's only national competition is a new government educational channel that advertisers' surveys say is watched by less than 5 percent of the viewing audience.

Elsewhere in Mexico, officials say, there are as many as 100 local cable services, most of which also broadcast U.S. news programs.

"We couldn't possibly keep track of them all, and it would be absurd even to try," one remarked. Moreover, he noted, thousands of Mexicans now own satellite dishes, which receive foreign television signals with no legal restrictions. And in the northern border region, more than 5 million Mexicans can receive U.S. telecasts with a simple roof antenna.

"Our policy toward broadcasting is essentially one of openness," the official said. "But when a Mexican company sells foreign television programming to Mexican customers, the Interior Ministry has an established legal right to regulate that programming."

With the increased exposure here to U.S. network news about Mexico, authorities have become increasingly vocal in their complaints. Manuel Alonso, President Miguel de la Madrid's chief public relations aide, recently took the unusual step of visiting U.S. television news executives, as well as key newspaper journalists, to express his government's view that recent U.S. media treatment of Mexico has been unfairly harsh.

By contrast, Televisa, which broadcasts a Spanish-language nightly news program to a potential audience of about 16 million Hispanic viewers in the United States, conspicuously refrains from critical commentary about the U.S. government, officials note.

The news program is broadcast via the Spanish International Network (SIN) as well as by a cable subsidiary of Televisa.

"The U.S. networks are quite aggressive in questioning Reagan's Central America policies, for example, but you'll never hear that kind of a negative view on Televisa," an official said.