Mexican authorities yesterday announced the arrest of a former federal security agent and two other men in connection with the disappearance of an American drug agent and ordered an investigation into charges that Mexican police had aided the escape of another key suspect.

A suspect identified as Tomas Morlet Borquez, said to be a former official in the Mexican Department of Federal Security, was arrested with two other men in northwestern Mexico, special correspondent William A. Orme Jr. reported from Mexico City. Their alleged role in the abduction was not disclosed.

The charge of complicity came Sunday from the head of the U.S. Drug Enforcement Administration, Francis M. Mullen Jr., who added in an interview yesterday that Mexican law enforcement officials have attempted to thwart other DEA investigations in Mexico.

"Mexico hasn't arrested a major drug trafficker in eight years," Mullen said.

"They were happy to have us come in and make a big headline once in a while . . . but when it finally started to hurt, when they thought we were getting dangerously close to the traffickers , they backed off." Other U.S. law enforcement officials, who asked not to be identified, confirmed a report in Newsweek magazine this week that a key suspect in the kidnaping of DEA agent Enrique Camarena Salazar was tracked by the DEA to an apartment in Mexico City on Feb. 14, but that Mexican officials failed to act for three days. By then, they said, he was gone.

Mullen said on Sunday that on Feb. 9, two days after the Camarena kidnaping, the DEA asked Mexican authorities to detain an airplane belonging to reputed Mexican narcotics czar Rafael Caro Quintero at the Guadalajara airport. Members of the federal security agency, Mexico's equivalent of the CIA, were guarding the plane, Mullen said, and allowed it to take off after talking at the scene with Federal Judicial Police, the Mexican equivalent of the FBI.

"They let the suspects get away. Then they start the raids," Mullen said in frustration yesterday.

In Mexico City yesterday, Attorney General Sergio Garcia Ramirez said officials are gathering information on the incident and will make a public explanation as soon as possible.

U.S. Ambassador John Gavin was expected to discuss the affair at a meeting last night with President Miguel de la Madrid. In Guadalajara, judicial police agent Fernando Inda offered local reporters his explanation of the Caro Quintero departure, Orme reported.

Inda said he and several DEA agents had traveled to the airport Feb. 9 on a tip that suspects were fleeing by private aircraft. There, he said, they stopped eight armed men who were about to board a private plane. The men displayed credentials of the Department of Federal Security and the Jalisco State Judicial Police, and Inda approved their departure, he said.

Other accounts state that as many as 50 men were at the airport guarding Caro Quintero with automatic rifles, only some of whom produced police identification, Orme reported. Inda "did not tell the whole story," one U.S. source said. "There is a whole lot more to it than that."

Other federal officials here said that witnesses in the Camarena case have been threatened and warned not to talk to the DEA. The officials said that some of the threats came from drug traffickers, and others were made by Mexican police.

Mullen said that frustration with Mexican drug enforcement efforts started long before the Camarena disappearance.

Last November, he said, Mexican officials initially tried to direct DEA agents away from a large plantation in Chihuahua where 10,000 tons of marijuana -- the largest single seizure ever made -- was found.

"The only statistic we have so far in that case is the prosecutor -- who was assassinated," Mullen said.

Meanwhile, an internal State Department memo indicates that Camarena was one of seven Americans, including a group of four Jehovah's Witnesses, who have disappeared in Mexico this year. Another 15 were abducted or disappeared last year.