MIAMI — Convicted terrorism plotter Jose Padilla will be resentenced in December after an appeals court concluded that his 17-year prison term was far too lenient for a trained Al Qaeda soldier and former violent gang member.

US District Judge Marcia Cooke set a Dec. 3 date for resentencing.

Prosecutors previously sought the maximum life sentence for Padilla but declined to say whether they would do so again.

Padilla, a 41-year-old US citizen,was convicted in 2007 of terrorism support and conspiracy charges. Prior to his indictment, he was held at a Navy brig for more than three years without charge as an enemy combatant.

When Cooke sentenced Padilla in 2008, she gave him credit for his time in the brig and provided other sentencing discounts totaling about 12 years below the 30-year minimum for his convictions. The US Court of Appeals for the 11th Circuit sided with the Justice Department in concluding Cooke committed several errors in not adding years for Padilla’s training at an Al Qaeda camp in Afghanistan and accounting for his 17 prior arrests.

‘‘Padilla poses a heightened risk of dangerousness due to his Al Qaeda training,’’ the court said. ‘‘He is far more sophisticated than an individual convicted of an ordinary street crime.’’

The US Supreme Court declined to hear Padilla’s appeal.

Padilla is being held in solitary confinement at the Supermax federal prison in Florence, Colo., said his attorney, chief federal public defender Michael Caruso. He said at a hearing Wednesday that he has ‘‘very limited’’ contact with Padilla because of prison restrictions regarding access.