On a desolate stretch of south Texas highway, sheriff's deputies responding to a routine disturbance call discovered a tableau of horror early this morning: the bodies of 17 people, most of them believed to be illegal immigrants, sprawled in and around a trailer at a roadside truck stop.

An 18th person recovered from the trailer died later in the day, making it the most lethal incident involving suspected illegal immigrants in at least 16 years. This afternoon, federal authorities arrested a man suspected to have been the driver of the tractor-trailer rig, which he had apparently abandoned about 175 miles north of the Mexican border along U.S. Highway 77.

Authorities said the dead -- among at least 62 people packed into the trailer of an 18-wheeler -- had apparently suffocated in the nearly airless, heat-baked container despite the efforts of some who tried to claw two holes through the foam insulation to admit fresh air.

Most of the trailer's human cargo was male. The youngest of the dead was a boy, perhaps 5 years old. Among the survivors was a girl who celebrated her 15th birthday today in an emergency shelter set up by local authorities. Sheriff's deputies brought her cake and cookies.

At least 44 survivors were picked up by local authorities, a few requiring hospitalization for dehydration and heat exhaustion and others found in twos and threes at roadsides throughout the day after initially trying to flee.

Local officials could not say how many hours, or days, the victims spent in the trailer before it was discovered about 2:30 a.m., nor where their trip originated, nor what they endured.

But police in the southern Texas town of Kingsville, about 100 miles south of the truck stop where the immigrants' journey ended, got a glimpse of their agony. It came when an emergency dispatcher received a 911 call from a man speaking Spanish and broken English at 11:42 p.m. Tuesday.

"He was saying, 'We're asphyxiating. Help me, help me. We're asphyxiating,' " said Sam Granato, chief of the Kingsville Police. "In Spanish, he said, 'We're in a trailer. We're illegals.' He goes on to say that there's 10 down, meaning that there's 10 people passed out, suffocating."

The call ended before a Spanish-speaking dispatcher could translate, Granato said. But it was only later, when the tape of the call was interpreted, that the message was clear.

Some time later, Granato said, a motorist called police to report he had seen what appeared to have been the same 18-wheeler -- with a hand protruding through a hole in the rear door as it drove north on Highway 77. "Apparently they managed to make some holes to try and wave bandanas to try and get attention from passersby," Granato said. "One was waving a bandana in front of a tail light."

Following a disturbance call, local law enforcement officials converged before dawn today on the Speedy truck stop just south of this town of Victoria, where the refrigerator trailer was discovered with its doors open. The trailer, parked in a lot behind the gas station, was white and unmarked except for its New York plates.

The officials found four bodies lying on the pavement near the truck and 13 more inside, one of whose bare feet were sticking out of the back. They said it was not clear how the doors had been opened, or by whom.

"This is not about numbers, it's not about jurisdiction," said Dexter Eaves, the Victoria County district attorney, who promised aggressive prosecution of the smugglers responsible for the incident. "We're discussing how to get every ounce of justice for these people that's coming their way -- whether that's from the federal or state government it matters not to us."

U.S. officials said the punishment under federal law could include the death penalty. "This case involves the greatest loss of life in recent history in what appears to be an alien smuggling case," said Asa Hutchinson, undersecretary for border and transportation security in the Department of Homeland Security, at a news conference in Washington. He called the case a "tragedy."

By late this afternoon, a half dozen of the immigrants remained hospitalized, most of them young and middle-aged men. And the dead remained in the trailer through much of the day as investigators gathered evidence.

"You can just imagine being one of 60 in a tractor-trailer with little to no ventilation," said Jerrel Robinowich, a spokesman for Detar Navarro hospital in Victoria. "They'd been out of the truck, in an ambulance before they got here, and they still showed up with a 105-degree body temperature. They were all very close to critical heat exhaustion."

The National Weather Service said it was 74 degrees with 93 percent humidity at 2 a.m., when the trailer was discovered. The high Tuesday was 91, one degree shy of a record for the date.

This evening, law enforcement officers were still searching for immigrants who were believed to be on foot in the area. Some officials said there may have been more than 100 people in the trailer, meaning three dozen or more may have been on the loose. After interviewing survivors, officials said that all appeared to be from Mexico, Guatemala or Honduras. Mexican consular officials from Houston were on the scene to help identify the dead.

The survivors, who were being cared for by the Red Cross and government agencies at a shelter, were described by officials as drained and disoriented. The authorities said they were giving conflicting accounts of their ordeal, making it difficult to piece together exactly what had happened.

"They are now at our local community center, receiving medical attention, water and food," Victoria County Sheriff Michael Ratcliff said.

The suspected driver of the rig, who was identified as Tyrone Williams, of Schenectady, N.Y., was arrested later in the day near Houston. His wife was reported to have said that he told her his rig had been hijacked.

The highways leading north from Mexico toward Houston and other Texas cities are frequent conduits for immigrants and drugs smuggled from south of the border. Small truckloads of illegal immigrants, usually tired but otherwise in good health, are apprehended so frequently that it barely counts as news in the area.

Today's case represents one of the deadliest of its kind, but it is not an isolated event. Last October, workers at a grain elevator in Iowa discovered 11 decomposed bodies of Mexican immigrants in a rail car. And in 1987, federal border agents found 18 Mexicans dead, with one survivor among them, in a boxcar in Sierra Blanca, Tex. The survivor told authorities that their smuggler had locked them in the boxcar in El Paso.

"This is an incredible tragedy," said Eaves, the district attorney. "There's a lot of people who would like to come to America and I can't blame them for that."

Brulliard reported from Austin.

Investigators go over trailer apparently abandoned at a roadside truck stop in Victoria, Tex., where bodies were found.