SAN FRANCISCO - A federal appeals court threw out the sentence of a man who was convicted of plotting to bomb Los Angeles International Airport to mark the start of the year 2000.

Ahmed Ressam had been sentenced to 22 years in prison on nine charges. Yesterday, the San Francisco-based U.S. Court of Appeals for the Ninth Circuit reversed his conviction on one of the charges; it sent the case back to a lower court to resentence him and explain the rationale behind the 22-year term.

Ressam was arrested near the U.S.-Canadian border in December 1999 after customs agents found 124 pounds of explosives in his car trunk as he disembarked from a ferry in Port Angeles, Wash. Prosecutors said he was intent on bombing the airport on the eve of 2000. The arrest raised fears of attacks and prompted the cancellation of New Year's celebrations at Seattle's Space Needle.

Yesterday's ruling 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 had been improperly convicted of carrying an explosive while committing a felony: lying on a customs form. The government failed to show that 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 Ninth Circuit to rehear the case with 15 judges. Prosecutors maintain that Ressam should get 35 years in prison.

Defense attorney Thomas Hillier II said the reversal "helps in fending off the government's argument that the original sentence was too lenient."

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

Over the next two years, according to court papers, he gave information on more than 100 potential terrorists and testified against coconspirator Moktar Haouari and Sept. 11 plotter Mounir el-Motassadeq. But his cooperation came to a halt by early 2003, resulting in charges being dropped against two other coconspirators.