By RALPH BLUMENTHAL
 
HOUSTON, March 23 - A jury on Wednesday convicted a trucker on human smuggling charges in the suffocation deaths of 19 illegal immigrants in South Texas in 2003, but spared him the death penalty by deadlocking on questions of how he was to blame.

On their third day of deciding the fate of the driver, Tyrone M. Williams, 34, a Jamaican from Schenectady, N.Y., the jury of seven women and five men found him guilty on 38 of 58 counts in Federal District Court here. But it also deadlocked on the other 20 counts, including conspiracy resulting in death, which carried possible capital punishment.

Judge Vanessa D. Gilmore declared a mistrial on the unresolved counts, leaving it up to the government to decide by next month whether to retry Mr. Williams, perhaps with three other defendants coming up for trial. Government and defense lawyers declined to speculate how Judge Gilmore might sentence Mr. Williams on the 38 counts of transporting illegal immigrants.

The charges stem from a bungled scheme by a smuggling ring that filled the trailer of Mr. Williams's 18-wheeler with at least 74 people from Mexico and Central America for transport through a Border Patrol checkpoint and deeper into Texas on the night of May 13, 2003.

With the truck's refrigeration unit turned off and the trip extended by hours because relief trucks were stopped at the checkpoint, desperate passengers clawed holes for air but succumbed to asphyxiation, heat and thirst. Mr. Williams abandoned the trailer with the bodies in Victoria and fled in the cab to Houston, where he sought medical treatment and claimed surprise that people had sneaked into his truck.

The confusing verdict, finding him guilty of smuggling but not determining his culpability in the deaths, left lawyers and the judge arguing over whether it was valid at all. But the judge ruled it was, declaring, "They took the death penalty off the table for not finding that he's a principal."

The verdict seemed to please Mr. Williams and his lawyer, who argued during the nine-day trial that the government had singled out his client as the first smuggling defendant to face the death penalty because he is black.

"He gave us all a big hug and thanked us," the lawyer, Craig Washington, said of Mr. Williams, who sat through the day's proceedings in a beige suit and orange tie. Mr. Williams's mother, Dorothy Williams, who attended the trial last week but then returned home, "has been praying for a miracle," Mr. Washington said outside court. "I'd say her prayers have been answered."

Mr. Washington, who presented only a single defense witness, a meteorologist who testified about the temperature and moonlight the night of the fatal ride, conceded in court that Mr. Williams had transported illegal immigrants. But he argued that greedy ringleaders had overloaded the truck.

The chief prosecutor, Daniel C. Rodriguez, an assistant United States attorney, put on the stand 21 survivors who gave harrowing testimony of failed 911 calls and screaming and banging to attract the attention of the driver and other motorists. The government's position was that Mr. Williams was in a crucial position to open the doors and save his passengers.

The deadlock was signaled in midmorning when the jury sent the judge a note that she read in court. It said the jury was "hopelessly deadlocked" on counts 1 through 20. It also said that on counts 21 through 58, jurors had agreed on guilt or innocence but were also hopelessly deadlocked on a series of questions they were supposed to answer after each finding of guilt.

Count 1 charged Mr. Williams with conspiracy to harbor and transport illegal immigrants, resulting in a person's death. Counts 2 through 20 were not death-penalty counts but charged him with harboring immigrants for commercial gain.

Verdict sheets handed out to the jurors called on them to find first whether Mr. Williams was guilty or not guilty of the count. If he was found guilty, jurors had to answer a series of questions, including whether Mr. Williams was a principal, or an aider and abettor or both, and whether injury or death resulted from his actions. On those first 20 counts, the jury could not come to any agreement.

On counts 21 to 39, which charged him in the transporting of people who survived, and 40 to 58, involving the riders who died, jurors agreed he was guilty. But they could not marshal the required unanimity in agreeing on the questions about Mr. Williams's role and whether he was responsible for injury or death.