Four Salvadorans suffocated and 12 others were left too weak to walk after being locked in the back of a tractor-trailer for an illegal journey from the Mexican border, authorities said yesterday.

Officials said the Salvadorans, including a 14-year-old and two 15-year-old girls, had paid $1,500 apiece to be smuggled into the United States from their Central American nation, which has been torn by guerrilla war.

Smugglers of illegal aliens had left the dead and weak Salvadorans in the rented truck after taking away "those that could walk" in another truck carrying more Salvadorans, said Hidlago County chief sheriff's investigator Erasmo C. Bravo.

The Salvadorans told authorities the smugglers then tried to set the truck on fire, he said.

A group of about 50 left El Salvador, traveled through Mexico and crossed the Rio Grande on foot, probably between Brownsville and Reynosa, and were picked up by two trucks on the United States side of the border, Bravo said.

"They knew they had some problems" by the time the trucks got to the outskirts of Edinburg, about 15 miles from the Mexican border, he said.

"So the second truck came by and opened the gate on the first truck -- you can't open it from the inside--because they were going to take only the ones who could still walk."

The others started crawling out and an unidentified woman driving by saw them. She called police on a citizens' band radio.