U.S. Ambassador to Mexico John Gavin said Thursday that 47 persons are in jail on charges related to the 1985 murder of U.S. drug enforcement agent Enrique Camarena Salazar, not that 37 were arrested and most of them released, as reported yesterday.

U.S. officials "know that there are at least 50" persons involved in the killing in Mexico one year ago of U.S. drug enforcement agent Enrique Camarena Salazar who remain at large, U.S. Ambassador John Gavin charged today.

In a press conference at the U.S. Embassy here, Gavin noted that Friday "marks the first anniversary of the kidnap, the torture and the assassination of our colleague, Enrique Camarena." To date, Gavin said, 37 persons have been arrested in Mexico in relation to the crime, including police officers, but at least 50 others "deeply implicated" have not yet been sought actively by Mexican law enforcement bodies.

The ambassador indicated that he was including in his figure persons connected to the crime through their efforts to shield principals in the case. Of the 37 arrested, most were subsequently released.

Gavin urged that Mexican authorities handling the case "prosecute it vigorously, and bring all of those involved, be they officials, traffickers of narcotics or other kinds of criminals, to the bar of justice."

This was the first time a ranking U.S. diplomat here has suggested on the record that Mexican officials not yet named or prosecuted were directly involved in the Camarena slaying.

A U.S. official who asked not to be named further charged that Miguel Angel Felix Gallardo, a fugitive accused drug boss who is said to have ordered Camarena's killing, has been seen publicly several times in Mexico in the past year and "has been receiving shelter and hospitality" from high-ranking officials of "at least two" state governments.

When investigations in the Camarena murder case first indicated widespread police complicity in the drug trade, officials in both countries predicted that out of concern for its image, Mexico would exert extraordinary effort to restrain the trafficking.

But U.S. officials say that diplomatic pressure and Mexican pledges of cooperation notwithstanding, the narcotics influx here has expanded, driven in part by Mexico's economic deterioration and still enjoying the protection of "elements" of Mexico's federal law enforcement hierarchy.

Although surpassed by the South America-South Florida axis, Mexico's northern frontier is a major narcotics entry point, U.S. officials say. Much of the Mexican marijuana and heroin sold in the United States is produced and exported by gangs based in Chihuahua, the biggest and among the least populated of Mexico's border states, local residents and U.S. experts say.

"Nobody likes to talk about it, but the narcotics traffickers are becoming an important economic power group here," said Francisco Barrio, an opposition gubernatorial candidate who hopes to turn alleged official protection of the trade into a potent campaign issue.

A U.S. drug agent said prominent ruling party politicians in the state are "known by everybody" to be deeply implicated in the drug trade.

"Government officials had to have been involved in the growth" of Chihuahua's illicit drug business, said Oscar Martinez, director of the University of Texas-El Paso Center for Inter-American and Border Studies.

Channeling the traffic through Chihuahua and other crossing points, Mexico is supplying American customers with a widening flow of marijuana, heroin and transshipped South American cocaine, U.S. narcotics and immigration agents said in interviews last week.

Border-area investigations have revealed "a significant, substantial increase in every one" of the three illicit drugs since mid-1985, said Phil Jordan, who heads the Dallas regional office of the U.S. Drug Enforcement Administration.

Larry Richardson, a U.S. Border Patrol division chief who monitors a 360-mile stretch of Chihuahua's boundary with New Mexico and Texas, said his agents "have noticed increases in both the size and the number of shipments here in the last four or five months."

U.S. customs checks in the Chihuahua border area in the past year have uncovered drug runners in record numbers with professionally doctored, false-topped campers, marijuana-packed tanker and produce trucks, and, most recently, pickup trucks outfitted with dummy propane cylinders that provided the first evidence of big-time overland smuggling of South American cocaine.

"Anything that you can think of, the traffickers here have tried it," Jordan said. Heightening the risks of border surveillance, narcotics trafficking has spawned a more violent and better armed breed of smuggler "who might be moving drugs one day and illegal aliens the next," Richardson said.

The most alarming new development, in the view of some U.S. narcotics experts, is Mexico's expanding output of a darker, stronger heroin known to American dealers as "black tar" or "tootsie roll."

A sticky, cocoa-colored powder worth $6,000 an ounce in West Texas and perhaps double that in northeastern inner cities, it is usually at least 60 to 70 percent pure, DEA agents report -- twice the strength of the traditional "Mexican brown" heroin that has been grown and refined in northwestern Mexico since the 1950s.

The black heroin's U.S. distribution, already detected in 23 states, is "almost completely controlled by Mexicans, through extended family connections," Jordan said. Still central to Mexico's heroin trade is the powerful Durango-based Herrera clan, which operates a network extending from the border to Chicago, U.S. agents say.

In 1984, Mexico is estimated to have supplied 34 percent of the heroin entering the United States, up slightly from 1983, with a similar additional increase detected in 1985, DEA spokesman Robert Feldkamp reported in a telephone interview. But the dramatically improved quality of Mexico's heroin is of greater concern, he stressed.

About a third of the cocaine coming into the United States today is smuggled through Mexico, the DEA calculates, an estimate unchanged since the Camarena killing first focused U.S. attention on the lucrative Mexican transshipment trade.

At the time he was killed, Camarena was one of several DEA agents investigating a Colombian-Mexican cocaine ring allegedly directed by Felix Gallardo, a former Sinaloa State security chief.