Mexico City — Mexico is becoming a key transshipment state for drugs from Latin America to the United States. Since the mid-1970s, Mexico has been a chief source of marijuana, opium, and heroin for illegal trade in the US. But tightened controls by US authorities at Miami airport and along the Florida coast have encouraged traffickers to reroute their merchandise across the Mexican-US border.
''While it's true that we've made great strides toward the elimination of this type of illegal activity, it's also true that producers and traffickers are trying to intensify their activities,'' Attorney General Sergio Garcia Ramirez told the press recently.
Mexican figures show that government forces destroyed almost twice as many drug plants - marijuana and opium poppies - from December 1982 to October 1983 as during the same period the previous year. Arrests of foreigners on drug charges doubled during that time, and those of Mexican nationals rose slightly.
Officials here attribute the resurgence of the drug problem to several factors. For example, Mexico's three peso devaluations in 1982 made dollar earnings through illicit drug trade extremely attractive.
US officials also blame newly established factories in Mexico for the rise in the drug trade. ''We have shifting markets in cocaine right now - factories moving into Mexico that have never been there before,'' said US Adm. Daniel Murphy, head of the US national narcotics border interdiction system under Vice-President George Bush.
''Drug dealers have reorganized and gotten more equipment,'' said Eduardo Andrade, spokesman for the attorney general's office.
''They go to places inaccessible to government helicopters,'' said Mr. Andrade. ''Some parts of the country are extremely arid and we never bothered to check them for drugs.
''Then, we found out that dealers had been growing crops using advanced watering techniques. So we decided to also put these areas under surveillance.''
Illicit production of marijuana, opium, and heroin in Mexico became a serious problem for the United States in 1974-1975 when Mexican production grew to meet the demand created by the elimination of the ''French connection.'' By 1975, 90 percent of the heroin consumed in the US came from Mexico. That year, Mexico launched, with US assistance, an extensive drug eradication program.
The Mexicans first tried cutting drug plants, then resorted to aerial spraying of herbicides - such as the controversial Paraquat. In 1976, Mexican and US authorities launched the Janus program, in which those accused of drug violations in one country could be prosecuted on the basis of court evidence from another.
The eradication effort was considered a success.
''Today, you can't find anything like the big fields of poppies that were photographed in the early '70s,'' said a US official familiar with the program. ''Now, you're talking about very small plots lodged in impossible areas like the bottom of a ravine. ''
One of the most effective anti-drug campaign measures, according to officials , was the decision not to prosecute farmers caught growing narcotic plants, but to let them off after a warning that repeat offenders would be tried. Instead, lawmakers concentrated on traffickers.
''The attorney general's office declined to press charges in more than 4,000 cases involving first-time offenders,'' says Andrade.
The recent increase in drug production and traffic dissappoints officials here. ''It seems the drug problem will be permanent,'' said Andrade. ''Dealers move on and start again as soon as the government destroys their crops.''