Despite U.S. pressures and a stepped-up Mexican investigating effort, there is still no trace of seven Americans who have disappeared since December in Guadalajara, Mexico's second-largest city.

The seven vanished in three separate incidents in a 10-week period -- five of them after being taken away, in view of witnesses, in cars driven by men who some witnesses assumed were plainclothed police making an arrest.

All U.S. citizens in their mid-thirties, the victims had little else in common besides their presence in Guadalajara, a pleasant, park-dotted metropolis of nearly 4 million that has emerged as a base for powerful Mexican narcotics rings.

There are 27,000 U.S. citizens living in Guadalajara, most of them retired, and they are thought to be the largest community of American retirees abroad. Nonetheless, Frank Bolex, president of the Jalisco State American Society, expressing a view widely held by the Americans, said last week that "there is no point in creating panic about Guadalajara."

In response to official U.S. displeasure over Mexican police failure to solve any of the apparent abductions, the attorney general's office here announced last week that a new federal office for the investigation of crimes against foreign visitors would be established.

The move was criticized by some Mexican observers. The daily newspaper La Jornada said in an editorial that the establishment of a special law enforcement office for foreigners represents "an implicit discrimination against Mexicans." But it was welcomed by U.S. Ambassador John Gavin as "a useful tool for the resolution of crimes" against Americans here.

President Miguel de la Madrid, in a speech Friday in the resort city of Acapulco, said Mexican officials "will redouble our efforts to avoid these lamentable incidents . . . that affect the security of foreign tourists." Mexico must "protect this source of foreign revenue," he said.

On the weekend, Mexican customs authorities cooperated in the closing of nine small U.S. border crossings after U.S. Drug Enforcement Administration officials received word that Mexican drug traffickers may try to kidnap another of its agents. Yet Mexico's new expressions of high-level concern have not translated into progress on any of the seven cases yet, U.S. officials complain.

Police investigations "seem to be going nowhere," one said, and the mystery surrounding the disappearances remains unsolved.

On Dec. 2, Dennis and Rose Carlsen, from California, and Ben and Patricia Mascarenas, from Nevada, were last seen being forced into an automobile in a quiet Guadalajara residential neighborhood where the Mascarenases, Jehovah's Witnesses engaged in door-to-door evangelization, had been living for a year. The Carlsens also reportedly were distributing religious literature at the time of their disappearance.

"We don't have the slightest clue as to where they might be," Edgardo Levy, a Jalisco State detective assigned to the case, said in a telephone interview last week. "This is the first case of its kind that we know of," Levy said.

Two months later, on Jan. 30, John Walker, from Minnesota, a Vietnam veteran and writer living in Guadalajara on a disability pension, went out on the town with a visiting friend, Alberto Rabelat, a Cuban-born naturalized U.S. citizen living in Texas. Neither has been seen since.

A week later, on Feb. 7, in an incident that has strained U.S.-Mexican diplomatic relations and underscored Guadalajara's growing importance as a center for narcotics traffic, U.S. Drug Enforcement Administration agent Enrique Camarena disappeared. He had left his office at the U.S. Consulate and was headed, unarmed, to lunch with his wife, when he apparently was lured into a car.

A $50,000 U.S. government reward offered for information on his whereabouts remains unclaimed.

In contrast with the previous six disappearances, however, the Camarena abduction had a readily apparent possible motive: as a liaison officer working openly for four years with Mexican police in Guadalajara, Camarena was one of the most visible U.S. narcotics agents working in Mexico.

When he disappeared, Camarena was working on "Operation Godfather," a joint U.S.-Mexican effort to crack what U.S. officials describe as "a major multinational cocaine trafficking group." His apparent kidnaping was seen by U.S. diplomats as "an arrogant demonstration of power" by the drug gangs that they fear could be repeated.

As in the apparent abduction of the Carlsen and Mascarenas couples, the kidnaping of Camarena was thought by some eyewitnesses to be an arrest by Mexican Federal Security Directorate agents, a supposition based on the kidnapers' cars, dress, and success in avoiding overt violence. But U.S. and Mexican sources say bodyguards of Guadalajara drug traffickers often use the methods and style of the Federal Security Directorate, sometimes displaying apparently valid agency credentials.

The reason for the disappearance of the Jehovah's Witnesses remains a matter of speculation. Guadalajara is a conservative, Roman Catholic city, and "a lot of people were known to be upset by the religious work of the Witnesses," Detective Levy said, among them some far-right groups connected to the private Autonomous University of Guadalajara.

There also is no apparent explanation for the disappearance of Walker and Rabelat, last seen Jan. 30 at a small restaurant in a section known for its seedy nightspots.

While the disappearances provide chilling evidence to some U.S. officials of the "impunity" with which kidnapers apparently can act in Guadalajara, the incidents have had little noticeable impact on U.S. and Canadian residents of the city and its bucolic environs, expatriates and U.S. diplomats agree.

"Crimes of violence like rape and assault are still almost nonexistent here," said Michael Eager, the Canadian-born manager of the Posada Ajijic Hotel and a 10-year resident of the area. "The foreigners here don't talk about the abductions that much. After all, if you are in Los Angeles or Toronto, every day people are being killed or beaten up."

"We know big cities have crime, but I'm not worried," said Joanne Biller, an American employed by a local real estate firm. "I know they're not after me."