BY CARA BUCKLEY

KEY WEST - A Cuban flight-crew member allowed by Fidel Castro's government to testify in a recent hijacking trial in Key West has defected to the United States.

Abilio Hernandez Garcia, a steward on the domestic DC-3 flight commandeered at knife point from Cuba to Key West in March, did not return to Cuba after testifying for the prosecution, according to the U.S. attorney's office.

The trial ended a week ago with the conviction of six Cuban men, who face minimum prison sentences of 20 years. Hernandez has left Florida and has traveled to a state out west, sources who spoke on condition of anonymity said.

Hernandez, who had an application pending with the Cuban Communist Party, was one of four crew members greeted by Castro in a televised meeting following the hijacking. He was then allowed to return to Florida to testify.

During his testimony, Hernandez said he was forced at knife point to the rear of the plane, where his hands were bound.

He also said he was treated badly at Krome detention center in West Miami-Dade and fed bad food.

Hernandez insisted he knew nothing about the hijacking plot, which defense lawyers claimed was accomplished with the complicity of the crew.

Mario S. Cano, the lawyer for one of the six convicted men, said Hernandez's defection will bolster his client's chances for an appeal.

''It solidifies our position with respect to a motion for a new trial,'' Cano said.

``The government's position all along was that none of the crew members wanted to stay.''

Prosecutors had no comment.