WASHINGTON -- The Bush administration wants the military jury that sentenced Osama bin Laden's former driver to reconvene for new deliberations that could add five years to his scheduled release date of Dec. 31.

In August, a six-officer panel convicted Salim Hamdan of providing material support to terrorism. It acquitted him of a more serious conspiracy charge and sentenced him to four months and 22 days beyond the time he had already served -- far less than the 30 years prosecutors sought.

Mr. Hamdan's sentence surprised the Bush administration, which had argued that prisoners like him presented such a threat to national security that they could not be tried on U.S. soil or in federal court. Jurors said the government failed to prove Mr. Hamdan was more than a minor functionary in al Qaeda.

Prosecutor John Murphy, a Justice Department attorney, initially said the government accepted the decision and called it "a victory for the system." But on Sept. 24, prosecutors filed a motion asking that the sentence be reconsidered. The Defense Department released the document Thursday, after inquiries by The Wall Street Journal.

The motion contends that the military judge, Navy Capt. Keith Allred, lacked authority to credit Mr. Hamdan for the time he served in pretrial confinement. Without such credit, Mr. Hamdan, who was captured in November 2001, would face an extra five years.

The chief Guantanamo prosecutor, Col. Lawrence Morris, said the government wants to clarify that unlike courts-martial, military commissions cannot credit defendants for time served.

"The length of the sentence is a matter of indifference to us," Col. Morris said. He said that if the jury still wants Mr. Hamdan released on Dec. 31, it could resentence him to however many days remained until then.

Lawyers for Mr. Hamdan opposed the motion, and said there was no legal basis to reconsider the sentence.

"In short, the administration's position is that it should have two opportunities to seek a sentence that it deems long enough," they said in a legal filing.

"I really am at a loss for words," said Lt. Cmdr. Brian Mizer, Mr. Hamdan's military defense lawyer. "The government, having stacked the deck, is now complaining about the hand it was dealt."

A civilian lawyer for Mr. Hamdan, Harry Schneider, said he believed the U.S. motion "is an effort to postpone the release date into a new administration."

During deliberations, jurors asked what credit Mr. Hamdan would receive, and fashioned a sentence that set his release date precisely on Dec. 31.

Hardy Vieux, a former Navy officer and a lawyer with the firm Blank Rome in Washington, said military judges routinely grant credit for pretrial confinement. "It's a fairness issue," he says.

For their part, defense lawyers have sought to hasten Mr. Hamdan's release date, arguing during trial that he deserves three days of credit for each day of the two years he spent in solitary confinement. Capt. Allred has yet to rule on that request.

Regardless of his criminal sentence, the government maintains it can hold Mr. Hamdan indefinitely as an unlawful enemy combatant. The government has not disclosed its plans for Mr. Hamdan, defense lawyers said.

Write to Jess Bravin at jess.bravin@wsj.com