Mexican and U.S. drug investigators, indicating that recent arrests here have crippled this nation's most important network for supply of marijuana to the United States, have turned their attention to an even larger cocaine smuggling ring.

Testimony last week from the accused marijuana traffickers has led authorities to suspect that a cocaine boss, who is still at large, was responsible for the slaying of U.S. Drug Enforcement Administration agent Enrique Camarena Salazar in February, U.S. and Mexican officials said.

The slaying of Camarena led to the recent crackdown, prodded by official U.S. outrage at the killing. Forty-four persons have been arrested during the past 10 days in what a senior DEA official described as the "most spectacular" series of drug busts in Mexican history.

U.S. officials here, and FBI director William H. Webster in Washington, have lauded the Mexicans' actions and expressed hopes for prosecution of high-ranking police officers whom some of the accused traffickers said they paid for protection.

The two most important arrests were of accused marijuana traffickers Rafael Caro Quintero and Ernesto Fonseca Carrillo. They admitted to heading huge operations for growing marijuana and sending it to the United States, according to Mexican and U.S. officials. The two prisoners later recanted much of their testimony, but under Mexican law it still can be used against them.

Caro Quintero, about 33, was a rising star in the Mexican drug trade. He was the owner of 8,000 tons of marijuana seized in November in Chihuahua State in the largest single marijuana bust in memory.

Fonseca, about 60, long had been considered the nation's principal marijuana trafficker, although DEA officials said Caro Quintero had surpassed him. Both men originally were from the Pacific coastal state of Sinaloa, and their operations allegedly were linked.

The two acknowledged that they planned the abduction of DEA agent Camarena during a party in Guadalajara on Feb. 4 because they wanted to question him about how much the DEA knew of drug operations here, U.S. and Mexican officials said. The two men also were considering trying to bribe Camarena, according to their accounts.

But both Caro Quintero and Fonseca denied having ordered the severe beating of Camarena that, they said, caused his death, and U.S. and Mexican officials said the accounts seemed credible. The testimony tended to support past suspicions that a third alleged crime boss, Miguel Felix Gallardo, was responsible.

The beatings were administered at a house in Guadalajara rented for Felix Gallardo, and his gunmen may have been present, according to the testimony. Kidnaped and killed at the same time was Camarena's Mexican pilot, Alfredo Zavala Avilar.

Felix Gallardo, about 37, is responsible for the operations in Mexico of one of the world's largest cocaine smuggling rings, according to U.S. and Mexican officials. Cocaine is produced in South America and flown to Mexico for smuggling into the United States, they said. The Mexican federal attorney general's office estimates that the ring delivers five to eight tons of cocaine monthly.

In November, the DEA helped to arrange a major cocaine bust on Mexican territory. The senior DEA source said his office now has fixed a new goal in the investigation: "Before, we were putting our full attention on Caro Quintero. Now the DEA is putting all its attention on Miguel Felix Gallardo. Eventually we'll get him."

According to the new testimony, five armed men grabbed Camarena Feb. 7 near the U.S. Consulate in Guadalajara as he was about to get into his pickup truck.

Fonseca allegedly saw Camarena and Caro Quintero briefly that evening. According to testimony, when Fonseca returned the next evening, he was informed by Caro Quintero that the DEA agent was nearly dead.

It is possible that Caro Quintero ordered the beating of Camarena, but if so, he may well have been acting in conjunction with Felix Gallardo, U.S. officials said. According to accounts from both men, Fonseca said to Caro Quintero, "You imbecile, . . . don't you realize what a tough spot you've put us in? This isn't just any idiot. This is a U.S. government employe."

The U.S. government, dissatisfied with the pace of Mexico's investigation after Camarena was grabbed, ordered rigorous customs inspections along the U.S.-Mexican border, slowing traffic. Then-DEA chief Francis Mullen publicy accused Mexican law officers of having let Camarena's abductors escape.

Caro Quintero had paid a $260,000 bribe to a state police commander to be allowed to fly out of Mexico after Camarena was killed, according to testimony. Caro Quintero subsequently was captured in Costa Rica, while Fonseca was arrested in the Mexican resort of Puerto Vallarta.

The arrest demonstrated that the Mexicans wanted to cooperate, U.S. officials said.

Mexican newspaper reports quoted Caro Quintero as saying he had 800 policemen on his payroll, and three agents of the Interior Ministry's plainclothed detective force who were arrested with Fonseca. When arrested, Fonseca was carrying an Interior Ministry identification card, bearing a false name, that would be very difficult to obtain without a good contact in the ministry, U.S. officials said.