MEXICO CITY, March 6 -- The owner of a department store in the provincial capital of Culiacan was driving to work one morning last September when three unmarked sedans without license plates surrounded his gray Oldsmobile.

As passers-by watched in terror, four men brandishing assault rifles hauled the man, Romulo Rico Urrea, from his car, forced him into one of theirs and sped away.

Mr. Rico has not been seen since Sept. 25, 1996. But a notebook dropped in his car by one of the kidnappers, as well as evidence gathered by military investigators, links the abduction to Gen. Jesus Gutierrez Rebollo, the former head of Mexico's anti-drug agency who was arrested last month on charges of collaborating with one of the country's most powerful cocaine barons.

Mr. Rico is one of at least 51 Mexicans who have disappeared in the last three years after kidnappings in which there were signs of Government security force involvement, according to lists compiled by relatives, human rights organizations and the press. Now, evidence is emerging to tie many of the abductions to the war against powerful drug traffickers, which has increasingly been under the command of Mexico's military.

''We are everyday citizens under attack, caught in the crossfire between narcos, authorities and narco-authorities,'' said Lucia Solis de Jurado, whose husband, a semiprecious-stone trader from the border city of Ciudad Juarez, was seized on the front step of his home on Oct. 6, 1996. ''It has gotten to the point where it can happen to anyone.''

A majority of the victims have no proven ties to drug traffickers or other criminal activities, relatives and human rights leaders contend, although a number have had brushes with the authorities.

''They tend to be businessmen, students and other citizens who were going about their lives,'' said Oscar Loza of the Commission for the Defense of Human Rights in the state of Sinaloa, where at least nine people have disappeared.

Mexico's military has traditionally played a supporting role in the fight against drug trafficking, mainly eradicating narcotics crops. Shortly after he took office in 1994, President Ernesto Zedillo, facing widespread corruption in the state and federal police, began to place military officers and troops in key positions in the battle against the drug cartels.

General Gutierrez was appointed Mexico's chief anti-drug official in December 1996, and army officers were given command of state and municipal police forces in Sinaloa, through which large quantities of drugs flow. Just last week, the army took over narcotics operations in the border state of Baja California.

A Growing Concern Over the Military's Role

Since the arrest of General Gutierrez, who was highly decorated, a number of families of missing Mexicans have come forward after enduring their anguish in silence for months and even years. The number of known victims is growing.

There is evidence that in addition to Mr. Rico, five men who disappeared since last September in northern Mexico were abducted in operations commanded by General Gutierrez and carried out by his deputies during his two-month tenure as head of the national drug agency or before that, when he was the senior commander of the Fifth Military Region in central Mexico.

The abductions in which General Gutierrez appears to have had a role are only a fraction of those reported. The general's lawyers did not respond to requests for comment.

The disclosures about the kidnappings raise new questions about General Gutierrez's ascent to the highest position in Mexico's war on drugs, and about Mr. Zedillo's moves to expand the role of the armed forces in the anti-narcotics campaign.

Several months before Defense Minister Enrique Cervantes Aguirre recommended General Gutierrez to the President for the top anti-drug job, the Mexican military had substantial evidence implicating the general's two closest aides in the kidnapping of Mr. Rico. Both aides were arrested with their commander on drug charges on Feb. 18.

The kidnapping allegations apparently never reached the highest levels. Mr. Cervantes acknowledged that neither he nor President Zedillo had had any doubts about General Gutierrez until about two weeks before his arrest.

Mr. Rico's relatives say they believe that he came under suspicion of drug trafficking because Miguel Angel Rico Urrea, his brother, was falsely accused on drug charges in 1992 and served prison time before he was cleared. A judge ordered his release, but the day he was to leave prison he was murdered.

Notebook Scribblings Reveal a Date and Place

On Sept. 16, 1996, soldiers in Culiacan swarmed into the home of Enrique Rico, another brother. The raid, conducted without a warrant, was led by a brash officer who identified himself with a name that later proved false. Romulo Rico was seized nine days later. At first, federal police agents told his relatives he was in custody at their headquarters.

But 24 hours later the same agents denied they had ever seen him, relatives said. At about the same time, Mr. Rico's wife of 33 years, Teresa, received an anonymous telephone call from a man who said her husband had been detained by someone named Horacio Montenegro Ortiz. The caller said he had seen Mr. Montenegro escorting his prisoner onto a military plane at the local airport.

The family did not recognize the name at the time, but it turned out to be significant. Mr. Montenegro, a former army captain, had long worked closely with General Gutierrez.

Later that day Mr. Rico's family discovered a notebook that one of his abductors had accidentally dropped between the front seats of his car. The scribbled, sometimes encoded phrases showed that the writer was a military officer who was in Sinaloa pursuing an inquiry into the murder in Mexico City on Sept. 14 of a leading anti-narcotics police commander, Ernesto Ibarra Santes.

The huge operation to find and capture Mr. Ibarra's killers was commanded by General Gutierrez, senior army commanders recently confirmed.

Unlike many families of the disappeared, the Ricos did not remain silent. They took the notebook to military and police authorities and human rights groups in the state and the capital, raising questions about the mysterious Mr. Montenegro.

In October, shortly before General Gutierrez was appointed commissioner of the National Institute to Combat Drugs, more than a hundred federal legislators signed a petition calling for a deeper investigation into Mr. Rico's kidnapping. And the military told the family that it was opening its own inquiry.

One man who took up the case was a newly appointed Attorney General, Jorge Madrazo Cuellar, a former human rights lawyer. But the Federal Judicial Police under his command steadfastly denied knowing anything about Mr. Rico, Mr. Madrazo said in an interview.

So he sent the Rico family to General Gutierrez, recently appointed to the drug agency at the time, thinking he was ''the right man to conduct the investigation.''

''We were surprised at how pleasant and friendly the general was,'' Mrs. Rico said bitterly in an interview. ''I thought I had finally found the person who was going to give me back my husband.''

In 10 meetings with her, Mrs. Rico said, General Gutierrez never acknowledged that he had directed the operations in Sinaloa at the time of her husband's kidnapping or that Mr. Montenegro had become his deputy in the drug institute, where the conversations took place.

As the Evidence Grows, Families Share Sorrows

Defense Minister Cervantes confirmed in a speech on Feb. 18 that Mr. Montenegro, ''a man with a disastrous reputation,'' was under military investigation for the Rico kidnapping. He added that last year General Gutierrez had disobeyed ''explicit orders'' from the high command to dissociate himself from Mr. Montenegro.

Another piece of evidence linking General Gutierrez to the kidnapping became clear after his arrest. Mexican television broadcast film of Capt. Javier Garcia Hernandez, an army intelligence officer and aide to General Gutierrez who was arrested on drug charges the same day as his commander.

Relatives who had witnessed the raid at Enrique Rico's home said they recognized Captain Hernandez as the brash officer who had commanded the search. In late February, military officials told the Rico family confidentially that the notebook in Romulo Rico's car belonged to Captain Hernandez.

In recent days, a half-dozen northern Mexican families, with nine disappeared relatives among them, have come together for somber meetings in the cramped Mexico City apartment where Teresa Rico and her children have taken refuge. They found one another through human rights organizations they had approached after General Gutierrez's arrest.

As they sadly share photographs of missing loved ones, they worry about their own safety. Human rights activists who helped them have received death threats, apparently to stop their publicizing disappearance cases. In interviews the activists confirmed the threats and asked not to be identified.

Gilberto Chaidez, the 22-year-old nephew of two hoteliers who were abducted from the border city of Tijuana, said he had broken down as he watched the televised announcement of General Gutierrez's arrest. Mr. Chaidez, a burly man with a buzz cut, had to stop to control his sorrow once again last week when he recalled his reactions.

''We were sure those men participated in kidnapping my uncles,'' Mr. Chaidez said. ''We thought it meant they would finally be released.''

Some Official Routes That Lead Nowhere

Rogelio Verber Mondaca, 39, is the father of two men who were kidnapped by uniformed army troops from a highway south of Tijuana on Jan. 6. Mr. Verber, who until a few years ago was the Deputy Police Chief of Tijuana, called on his friends in local law enforcement to help him mount a statewide search for his sons Rogelio and Raul, to no avail.

His son Rogelio, 28, suffers from advanced Hodgkin's disease and has a catheter in his heart for treatment, Mr. Verber said. He produced news photographs and clippings showing that General Gutierrez was conducting anti-drug operations in the area at the time his sons disappeared.

Mrs. Jurado and her family have become outraged about the official response to their quest for her husband, Ruben Guillermo Jurado, 39. A senior official of the state of Chihuahua, where the Jurados live, confirmed in an interview this week that Mr. Jurado had been seized by armed men wearing federal drug police uniforms.

Nevertheless the official, who insisted on anonymity, said state investigators believed that Mr. Jurado might have been kidnapped by drug traffickers, because of ''narcotics-related wrapping materials'' found in his home.

The Jurado family indignantly accused the authorities of inventing charges against Mr. Jurado. They point out that the police never searched his residence or workshop, before or since he disappeared.

Some relatives have nearly despaired of going through Mexican institutions. Maria de los Angeles de Beltran, whose husband, Manuel, disappeared in 1994, wrote to the United States Secretary of State, Madeleine K. Albright, pleading for help.

''Our Government doesn't fight drug trafficking,'' Mrs. Beltran wrote angrily. ''It just administers it.''