SAN FRANCISCO — A federal appeals court yesterday threw out the sentence of a man who was convicted of plotting to bomb Los Angeles International Airport at the turn of the millennium.

Ahmed Ressam was arrested near the American-Canadian border in December 1999 after customs agents found 124 pounds of explosives in the trunk of his car as he disembarked from a ferry in Port Angeles, Wash.

Prosecutors said he was intent on bombing the airport on the eve of the millennium. The arrest raised fears of terrorism attacks and prompted the cancellation of New Year’s celebrations at Seattle’s Space Needle.

Ressam was sentenced to 22 years in prison after being convicted off all nine charges. Yesterday, the 9th U.S. Circuit Court of Appeals in San Francisco reversed his conviction on one of the charges and sent the case back to a lower court to issue a new sentence and explain the rationale behind the 22-year term.

The decision does not necessarily mean Ressam will get a shorter term. Federal judges are given wide latitude to sentence defendants as they see fit.

Two of the three appellate judges said Ressam was improperly convicted of carrying an explosive while committing a felony: lying on a customs form.

The government failed to show the “explosives somehow aided or emboldened” him to provide a false name at the border, Judge Pamela Rymer wrote.

Emily Langlie, spokeswoman for U.S. attorney John McKay in Seattle, said the government was considering whether to ask the 9th Circuit to rehear the case with 15 judges. Prosecutors maintain Ressam should get 35 years in prison.

Ressam’s attorneys did not immediately returns calls seeking comment.

After his conviction in 2001, Ressam began cooperating with authorities in hopes of winning a reduced sentence. He faced a maximum of 65 years in prison.

Over the next two years, according to court documents, he provided information on more than 100 potential terrorists and testified against co-conspirator Moktar Haouari and September 11, 2001, plotter Mounir el-Motassadeq.

Ressam told authorities he saw Zacarias Moussaoui at a training camp in Afghanistan in 1998. He also told investigators about the type of shoe bomb Richard Reid attempted to detonate on an American-bound airline flight in 2001, and provided information about a network of Algerian terrorists in Europe.

U.S. District Judge John Coughenour of Seattle, who sentenced Ressam, said the information he provided was “startlingly helpful.”

But Ressam’s cooperation came to a halt by early 2003, resulting in charges being dropped against two other co-conspirators. His lawyers said years of solitary confinement, broken by periods of intense interrogation, had taken their toll on his mental health and corrupted his memory.