About 30 marijuana growers participated in what is being called "The Day of the Dead Massacre" of 22 policemen in Mexico's southeastern swamplands, the federal attorney general's office here said today.

The killings took place on the eve of the day Mexicans commemorate their dead. It was the largest loss of life from a single clash in Mexico's drug wars and has prompted a massive manhunt. About 100 state and federal police and 500 troops from an Army narcotics eradication squad patrolled southern Veracruz State looking for the killers of the Mexican police officers, whose bound and bruised bodies were discovered Saturday.

The 22 policemen were captured and killed by about 30 heavily armed men, "every one of them" a resident of a remote farming community about 15 miles south of the Gulf of Mexico port city of Coatzacalcos, said Federal Judicial Police Cmdr. Florentino Ventura.

Sixteen arrests have been made so far, and information from the suspects "will soon lead us to those responsible," Ventura said in a telephone interview.

The 16 suspects now being interrogated will be able to identify the organizers of the attack and of the marijuana growing operation "that the assailants were protecting," Ventura said.

The victims, shot through the backs of their heads, were members of the Federal Judicial Police, the Federal Security Directorate, the Veracruz State Public Security Directorate and the Veracruz State Judicial Police, Ventura said.

"This is the price Mexico is paying for confronting these faceless criminals," Mexican Attorney General Sergio Garcia Ramirez, in Veracruz supervising the investigation, said by telephone last night.

The ambush took place in Hidalgotitlan, an isolated municipality of cattle ranchers and grain farmers in the sparsely settled Tehuantepec Isthmus lowlands. Larger than the state of Delaware, with vast tracts of marsh and rain forest separating stretches of fertile savannah, the region has few roads but is "full of landing strips, many of them clandestine," Francisco Fonseca, chief spokesman of the attorney general's office, said here.

Marijuana cultivation is widespread in the zone and patches of opium poppies were discovered recently, Fonseca said.

"The problem is economic, and the peasants are the last people we should blame," he said. "It is a depressed area, and the traffickers are able to pay them $20 for a little crop of marijuana when they would earn maybe $2 for the same amount of corn."

Army troops dispatched to the area to search for the killers had been conducting a sweep of the neighboring state of Oaxaca, now believed to be Mexico's largest narcotics production area, Fonseca said.

Mexico is said by U.S. authorities to be the source of one-third of the heroin and perhaps one-fifth of the marijuana imported into the United States, as well as the conduit for as much as one-third of the South American cocaine brought into the United States.

Apparently lured into an ambush by drug traffickers Friday in a remote district of Veracruz State, the police fled on foot but were soon surrounded by a large gang of heavily armed attackers, according to an account by two witnesses, Fonseca said. The witnesses, local police informants, said they escaped into the bush as the gunfight began, Fonseca added.

"When the police arrived, the drug traffickers rounded up a group of local marijuana growers, people whom they supplied with weapons," Fonseca said. "The witnesses guessed that there were about 40 attackers, but from the duration and scale of the battle, it appears that there may have been as many as a hundred."

The police, who apparently had been en route to a nearby farming settlement before intercepting and following a confessed drug smuggler to the site of a marijuana pickup, ran out of ammunition in the gunfight, Fonseca said. The police were then captured, bound and killed, and their bodies were carried downriver by boat, he said.

Among the suspects being interrogated, Ventura confirmed, is a state judicial police commander stationed in the nearby city of Acayucan.