The Defense Department is changing several rules governing its military trials of terrorism suspects held at the U.S. naval base at Guantanamo Bay, Cuba, department officials said yesterday.

Pentagon officials portrayed the changes as improvements to a process they have repeatedly asserted assures all defendants a full and fair trial. Some private legal experts welcomed the changes but said they did not go far enough and did not address some of the most objectionable features of the trial system.

At a Pentagon news conference in which he announced the procedural changes, Air Force Brig. Gen. Thomas L. Hemingway declined to say whether the adjustments amounted to major changes or minor tinkering.

"This will make for a more orderly process," Hemingway said. Asked whether the changes make the trials more fair, he replied, "Ultimately it might be, in the eyes of some people."

He said the most significant changes pertain to the duties of the presiding officer of the trials, or commissions. Under the new rules, the presiding officer is more like a judge in a court martial or civilian court and is required to rule on all questions of law; the other members of the commission will function more like a jury and are no longer permitted to participate in deciding most legal questions, Hemingway said.

The presiding officer can no longer vote with commission members on findings of guilt or innocence and sentencing. However, a majority of the other commission members may overrule the presiding officer on rulings regarding the admissibility of evidence, as was the case previously.

Eugene R. Fidell, president of the National Institute of Military Justice, said the changes make the Guantanamo Bay proceedings more like those of a military court martial, which he called a step in the right direction.

Other legal experts said the process was still flawed.

"There still is no appeal to an independent civilian court," said Kenneth Roth, executive director of Human Rights Watch, a New York-based organization. Referring to U.S. Defense Secretary Donald H. Rumsfeld, he added: "The commissions still have Rumsfeld or his designate serving as prosecutor, judge, appellate judge and potential executioner. That has not changed one iota."

Trial proceedings were begun last summer against four suspects, including Salim Ahmed Hamdan, a Yemeni. But the process was halted after a district court ruled in November that he could not be tried by a military commission unless a "competent tribunal" determined that he was not a prisoner of war under the Geneva Conventions. The commission had not begun hearing evidence when the trial was halted.

In a ruling in July, a three-judge panel of the United States Court of Appeals for the District of Columbia Circuit ruled that the commission itself was such a competent tribunal, and that Hamdan could assert his claim to prisoner of war status at the time of his trial before a military commission.

Hemingway said he could not forecast when the four suspended trial proceedings would be resumed. The Pentagon says it is holding 505 prisoners at the Guantanamo Bay prison compound, which opened in January 2002.