Cocaine Seizure Sets Record at Border : Drugs: Nearly four tons seized in San Diego is the second-largest haul in California, authorities say.

Nearly four tons of cocaine found Thursday in a propane tanker en route from Mexico is the largest cocaine bust ever recorded at a U.S. land border crossing, federal authorities declared Friday.

The haul--with an estimated street value of $262.5 million--is believed to be the second-largest amount of cocaine ever seized in California, after the record-busting cache of 21 tons discovered last year in a warehouse in the San Fernando Valley community of Sylmar.

Meanwhile, U.S. and Mexican officials were conducting a two-nation manhunt for the driver, who was permitted to leave the Otay Mesa port of entry in San Diego after officials searching the suspicious-appearing truck were at first unable to discover the hidden drug cache, which amounted to 7,702 pounds.

The search for drugs dragged on for almost 1 1/2 days, authorities said, because inspectors first decided to take apart the rig’s 18 tires and later had to drain excess propane, which is highly volatile, from inside the tank.

Investigators did not discover the cocaine until about 2:30 p.m. Thursday--32 hours after the vehicle had first pulled into the Otay Mesa port of entry, and about 24 hours after the driver had been permitted to leave.

The driver, a Mexican national whose name was not released, had been detained for at least eight hours. He was allowed to go free, U.S. Customs officials said, because, despite the ongoing search of the truck, there was no legal basis to detain him further.

“We can’t hold someone indefinitely at the border,” said Thomas W. Hardy, acting district director for the U.S. Customs Service in San Diego. “I can’t say there was an error; we’re looking into that.”

Inspectors first became alerted to the truck when drug-sniffing dogs stationed at the facility drew attention to the vehicle’s tires, officials said. When inspectors weighed the truck, which was supposed to be empty, they found it to be suspiciously heavy. Authorities said they had had no advance information that the vehicle might be ferrying drugs.

The bust, officials said, shows the wide use that international traffickers are making of the U.S.-Mexico border, which stretches for almost 2,000 miles from Texas to California and has historically been a smuggling corridor.

Smugglers make use of the vast unguarded spaces between ports of entry, and also frequently try to sneak drugs through the ports in vehicles, as happened in this case, in hopes that the understaffed inspection force will not search their cargoes. Tens of thousands of cars and trucks enter the United States each day from Mexico, making it impossible to search each vehicle.

“They (the traffickers) never stop being innovative,” said Julius Beretta, special agent in charge of the U.S. Drug Enforcement Administration in San Diego. “Something like this leads you to wonder how many times it has happened (before). We just don’t know.”

Last year, 589,000 trucks--more than 1,613 per day--entered U.S. territory via the Otay Mesa port of entry. They carried about $4 billion in cargo.

The tanker truck was carrying propane gas for Hidro Gas Juarez, a firm based in Ciudad Juarez, Mexico. Company officials could not be reached Friday. U.S. authorities said the firm was cooperating in the investigation.

In 1985, said Customs spokeswoman Bobbie Cassidy, inspectors discovered two separate loads of marijuana totaling 135 pounds in the tires of two Hidro Gas Juarez trucks.