The Mexican government filed narcotics and arms trafficking charges today against ex-fugitive Rafael Caro Quintero. U.S. officials said they had been told that he also would be charged later in the kidnaping and murder of a U.S. Drug Enforcement Administration agent two months ago.

The Mexican national attorney general's office assigned Caro Quintero to a court and filed the charges four days after he was captured in Costa Rica and quickly deported to this capital. He and several associates were to be formally arraigned on Tuesday, court sources said.

Under intensive police interrogation, Caro Quintero has confessed to running a huge network for growing and marketing marijuana, according to U.S. officials and Mexican press reports. But Caro Quintero has denied playing any role in the kidnaping and murder of DEA agent Enrique Camarena Salazar, according to these sources. The U.S. government has pressed the Mexicans to find Camarena's killers and Caro Quintero has been considered a leading suspect.

A senior DEA official here, who asked not to be named, said it might be difficult to convict Caro Quintero in the killing of Camarena, but he thought the Mexicans were carrying out a sincere investigation and would take action against police corruption that has come to light in the case.

"The Mexicans will definitely do something about their internal problems," the DEA official said, adding that the government here was "absolutely" committed to crack down on narcotics trafficking.

The senior DEA officials said that Caro Quintero would be charged in the Camarena case by authorities in the state of Jalisco, where the abduction took place. But he noted that the known evidence against Caro Quintero was such that the outcome could not be foreseen.

Two Jalisco state policemen testified that they participated in the kidnaping and delivered Camarena to Caro Quintero after the abduction. They later recanted, however, saying that their testimony had been given under duress.

"It's not a shut type of case," the DEA official said. But he added that Caro Quintero could receive the maximum prison sentence of 40 years if convicted of the narcotics trafficking charge and would not be eligible for parole. He said 40 years in prison is the maximum penalty allowable under Mexican law for any crime.

Under interrogation, Caro Quintero described in detail his own marijuana operation and claimed that he had 35,000 persons working for him, according to U.S. officials. He said that he was the principal owner of 8,000 tons of marijuana seized by authorities in November in Chihuahua state.

Caro Quintero also named three of his principal buyers in the United States but said that two of them had died in a plane crash in November, U.S. officials said. The identity of the third buyer, who was said to live in Los Angeles, was one of the few fresh leads that the DEA obtained from the Mexicans' interrogation of Caro Quintero, the DEA official said.

"He's the only live wire that we have in the states," the DEA official said. "My opinion is that he Caro Quintero is holding back on some very important things."

The Mexicans were holding Caro Quintero under very tight security, and kept secret his location for much of the time that he was under interrogation. Newspapers and some officials suggested that authorities were afraid that corrupt police might try to kill Caro Quintero to prevent him from providing information about official involvement in drug trafficking.