WASHINGTON, Feb. 23 - Pentagon officials say they do not expect to be able to provide space for representatives of human rights advocacy groups to observe any military tribunals at the naval base at Guantánamo Bay, Cuba, prompting complaints from those groups that the military is trying to shut out potential critics.

In letters last week to Amnesty International, Human Rights First and Human Rights Watch, a senior military official said it was unlikely that they would be allowed to attend any military tribunals at Guantánamo. The official, Brig. Gen. Thomas L. Hemingway, a chief legal adviser in the office of military commissions, wrote that space would be limited if and when tribunals were held at Guantánamo.

"It is expected that limited courtroom seating and other logistical issues will preclude attendance by many who desire to observe military commission proceedings," he wrote.

General Hemingway noted that there would be seats for the news media as well as for representatives of the International Red Cross.

Last Friday, the groups wrote to the defense secretary, Donald H. Rumsfeld, asking him to reconsider the matter, saying, "There can be no legitimate governmental reason for denying our access to the proceedings."

Wendy Patten, a Washington representative of Human Rights Watch, said Monday that the reasons given were implausible and that the groups should be entitled to at least one seat that they could rotate among themselves. She noted that the Bush administration had defended itself from critics of the possible tribunals by saying that the proceedings were to be open to wide scrutiny.

A senior military official said the deliberations over whether to allow the presence of human rights groups involved issues other than the availability of seats in the courtroom and the overflow room where some reporters will be able to view the proceedings on closed-circuit television. The official, who spoke about the deliberations on the condition of anonymity, said that planners considered the problems of security as well as limited food and housing facilities at the Guantánamo base, which is in an isolated location on the southeastern tip of Cuba.

The official acknowledged, however, that there would probably be arrangements for some members of Congress to attend the trials and perhaps for officials of organizations that represent victims of the Sept. 11 terrorist attacks.

President Bush has designated six of the 650 prisoners at Guantánamo as eligible for trial but there have, as yet, been no specific plans to conduct any tribunals. More than 80 members of the news media, both from the United States and abroad, are expected to attend any tribunals, officials said.