Agents Seize 3 1/2 Tons of Cocaine at Border : Crime: Driver of propane truck is released while authorities spend more than a day emptying tanker.

Federal agents Thursday seized what they believe is more than 3 1/2 tons of cocaine from a propane-filled tanker truck, the largest volume of cocaine ever confiscated at the California-Mexico border, authorities said.

Drug Enforcement Administration and U.S. Customs agents discovered the cocaine at 2 p.m. Thursday after spending nearly 30 hours bleeding propane from the Mexican tanker.

Agents stopped the northbound truck about 6:30 a.m. Wednesday at the Otay Mesa border cargo inspection station after noticing it was nearly 7,500 pounds heavier than it should have been.

The driver, a Mexican whose name was withheld, was allowed to leave the scene because federal officers were unable to readily determine Wednesday whether drugs were inside.

Tom Hardy, acting district director for the U.S. Customs office in San Diego, said his agency was seeking to find the driver, who could face life in prison and a $4-million fine if caught, charged and convicted of cocaine smuggling.

“We just couldn’t hold him an inordinate amount of time,” Hardy said. “Right now he’s at large.”

Agents estimated the seizure at more than 3 1/2 tons, although the exact amount of cocaine in the Hidro Gas Juarez tanker was uncertain late Thursday because heavy fumes slowed the unloading of the drug.

The seizure--which federal officials estimated to be worth $85 million wholesale and $425 million at street prices--is the largest ever in San Diego County and the second-largest ever in Southern California. A world-record 21 tons of cocaine was discovered at a San Fernando Valley warehouse a little more than a year ago.

The tanker was loaded with loose bricks of cocaine cut into kilos, some wrapped in plastic bags and some wrapped in cellophane. One law enforcement official said it is impossible to determine exactly how much cocaine was inside because the truck’s weight was not known.

“If the truck was filled with steel, the total amount of cocaine could be less,” the source said. “Then again, it could be a lot more, almost up to 10 tons. The tanker was loaded to the gills.”

The truck’s manifest, which shows its destination, indicated the truck had nothing more than gas inside. Federal agents became suspicious because of the weight discrepancy and held the truck overnight at the border crossing. On Thursday, they used narcotics-sniffing dogs, which detected cocaine inside, Hardy said.

Agents could not get into the truck until 2 p.m. Thursday because of the gas and fumes.

Members of the San Diego Fire Department bomb squad, fire investigation unit and hazardous-materials unit checked for explosives inside before agents entered.

Hardy said the U.S. Customs district in San Diego had seized 200 pounds of cocaine during the fiscal year ended last week. During the fiscal year before that, it seized 3,135 pounds.

One drug enforcement official said late Thursday that propane tankers are more typically used by smugglers to haul marijuana. Cocaine is usually transported in commercial trucks, he said.

The largest-ever drug bust occurred in late September, 1989, when federal agents seized almost 20 tons of cocaine--worth an estimated $6 billion on the street--at a warehouse in the San Fernando Valley community of Sylmar. Agents confiscated an additional $12.2 million in cash there.

Seven men were arrested in what Los Angeles County Dist. Atty. Ira Reiner later said was part of a massive operation that had funneled at least 60 tons of drugs into the country during 1988 and 1989.

At the time, the Drug Enforcement Administration said the Sylmar seizure represented about 5% of the world’s annual production of cocaine--more than growers in Peru, the world’s largest supplier, can produce in a month.

“This is not just powder on the table,” Donald Hamilton, a DEA spokesman, said at the time. “It’s more like powder on the football field.”

Investigators later determined that the Sylmar operation was linked to warehouses in El Paso and Ciudad Juarez, Mexico.

In May, 1989, U.S. Border Patrol and Customs agents seized 969 pounds--or 0.485 of a ton--of cocaine worth a street value of $60 million from youths who were carrying the drug in duffel bags across the border just southeast of Imperial Beach.

That same month, Border Patrol agents seized 767 pounds of cocaine at the San Onofre checkpoint.

The largest San Diego-area border seizure had been in September, 1986, near Jacumba, when 1,285 pounds, or 0.64 of a ton, were confiscated.