A US federal judge has ruled five Algerian men be freed because they were held unlawfully in the Guantanamo Bay for nearly seven years.

The judge, Richard J. Leon of Federal District Court in Washington, also ruled that a sixth Algerian man was being lawfully detained because he had provided support to the terrorist group al-Qaeda.

The one detainee Judge Leon found to be lawfully held, Bensayah Belkacem, has been described by intelligence agencies as a leading al-Qaeda operative in Bosnia.

The case was an important test of the Bush administration's detention policies, which critics have long argued swept up innocent men and low-level foot soldiers along with high-level and hardened terrorists.

The six men are among a group of Guantanamo inmates who won a Supreme Court ruling that the detainees have constitutional rights and can seek release in federal court. The 5-4 decision said a 2006 law unconstitutionally stripped the prisoners of their right to contest their imprisonment in habeas corpus lawsuits.

The hearings for the Algerian men, in which all of the evidence was heard in proceedings that were closed to the public, were the first in which the Justice Department presented its full justification for holding specific detainees since the Supreme Court ruling in June.

Judge Leon, in a ruling from the bench, said that the information gathered on the men had been sufficient to hold them for intelligence purposes, but was not strong enough in court.

"To rest on so thin a reed would be inconsistent with this court's obligation," he said. He directed that the five men be released "forthwith" and urged the government not to appeal.

It was not immediately clear whether the government would appeal, but some lawyers said they considered an appeal likely.

Judge Leon, who was appointed by President Bush, had been expected to be sympathetic to the government. In 2005, he ruled that the men had no habeas corpus rights.

Lawyers said the decision was likely to be seen as a repudiation of the Bush administration's effort to use the detention center at the American naval base at Guantanamo Bay, Cuba, as a way to avoid scrutiny by American judges. President-elect Barack Obama has promised to close the prison.

"The decision by Judge Leon lays bare the scandalous basis on which Guantanamo has been based - slim evidence of dubious quality,” said Zachary Katznelson, legal director at Reprieve, a British legal group that represents many of the detainees. "This is a tough, no-nonsense judge."

The government argued that the six Algerians, who were residents of Bosnia when they were first detained in 2001, were planning to go to Afghanistan to fight the United States and that one of them was a member of al-Qaeda.

The case has become an example of the Bush administration's pattern of changing strategy in its long legal war over Guantanamo as the courts have scrutinized the government's justification for its detention policies in general and its reasons for holding individual detainees.

In 2002, President Bush made the government's allegations against the men a showcase of his administration's approach to dealing with terrorists. He said in his State of the Union address that the six men had been planning a bomb attack on the United States Embassy in Sarajevo, Bosnia. Last month, however, Justice Department lawyers said they were no longer relying on those accusations to justify the men's detention.

HSH/HAR