The head of the Drug Enforcement Administration yesterday accused Mexican police of giving safe passage out of Mexico to a reputed drug kingpin suspected of involvement in the kidnaping of a veteran U.S. narcotics agent.

DEA Administrator Francis M. Mullen Jr. said that reputed Mexican narcotics czar Rafael Caro Quintero flew out of Mexico Saturday night to an undisclosed location under the protection of Mexican federal police, after being briefly detained by a separate police force in Guadalajara.

"I don't know if I would go so far as to say cover-up," Mullen said on ABC-TV's "This Week With David Brinkley."

"But there may be some complicity at the lower levels of law enforcement."

Mullen's remarks were the strongest so far from a Reagan administration official directly accusing Mexican law enforcement officials of deliberately obstructing the probe into the kidnaping of DEA agent Enrique Camarena Salazar.

U.S. officials had previously accused the Mexicans only of not moving aggressively enough to investigate the Feb. 7 kidnaping, and privately said four other suspects escaped because of slow police work.

In Mexico City, a Mexican government spokesman who asked not to be named said there would be no official response to Mullen's accusations until the government there received a complete transcript of his remarks, Washington Post special correspondent William A. Orme Jr. reported.

This official said the Mexican government would "welcome information from Mr. Mullen or anyone else" regarding Caro Quintero's departure.

U.S. frustrations with the Mexican authorities in this case led to exhaustive car-by-car searches last week of Mexican travelers crossing the border into this country. Mullen said yesterday that those searches, which paralyzed border traffic for most of last week, will now be replaced by spot checks.

Those searches, he said, were conducted partly to get the Mexican government's attention because of a widespread feeling in the administration that not enough was being done to find the missing DEA agent.

"One of those traffickers involved in the kidnaping was spotted in an aircraft leaving Guadalajara on Saturday night," Mullen said. "He was stopped by Mexican police, the judicial police, and allowed to leave, and I learned that he had as protection members of the DFS" -- the Direccion Federal de Seguridad (Federal Security Directorate).

The DFS is a plainclothes detective force controlled by the Interior Ministry. The Federal Judicial Police, which falls under the attorney general, has been coordinating Mexico's crackdown on narcotics trafficking.

"So you had police protecting, and another element of the police letting this individual go for whom there is a warrant outstanding," Mullen said. "This concerns us, and we wonder why he was allowed to leave."

Caro Quintero is the reputed patriarch of the Caro family, one of Guadalajara's largest narcotics trafficking clans, and is said to own a marijuana plantation that has produced 3,500 tons of Mexican herb. For the past decade, the Caro family has repeatedly been implicated in opium poppy and marijuana cultivation, and is believed to have formed ties recently with Colombian cocaine smugglers, who increasingly use Mexican territory as a transit point.

Caro Quintero, a multimillionaire said to have extensive real estate holdings and other business interests, is believed by some to have been one of the financiers of a massive marijuana growing and marketing scheme exposed by Mexican police last November. At the operation's warehousing center, located close to the Texas border in the remote desert country near Big Bend National Park, authorities confiscated nearly 9,000 tons of marijuana, believed by U.S. government experts to be a world record seizure.

Caro Quintero is also suspected of involvement in the recent murder of several Guadalajara policemen. He was immediately a suspect in the Camarena case, officials said, and local Mexican police reported searching a Caro ranch near Guadalajara looking for clues.

Yesterday, Mullen also accused Mexican authorities of allowing other known Guadalajara drug dealers, whom he did not name, to leave Mexico before being questioned about Camarena's disappearance. "Because of the slowness in getting into the investigative activity, all of these people are gone, some as far as Europe," he said. "It seems to me they were given adequate time to depart the area."

About 25 potential suspects, he said, were granted special court injunctions -- called an amparo in Spanish -- protecting them from questioning or searches without the express approval of a district judge, a procedure in which police must first show "probable cause" for their suspicions. Mullen said U.S. officials were "startled" by the scope of this court order.

Camarena was the seventh U.S. citizen to disappear in Guadalajara in less than three months. There have been no hard leads as to any of their whereabouts, U.S. officials said.