Even so, lawyers for the humanitarian groups said they were heartened by the ruling. It came seven weeks after many of the same plaintiffs won a ruling in a separate but related case before a federal appeals court based in San Francisco. The 9th U.S. Circuit Court of Appeals found in that case that a 1996 antiterrorism law that prohibited anyone from providing "training" or "personnel" for terrorist groups was also too vague to pass constitutional muster.

In recent months, other courts have also challenged the Bush administration's designation of enemy combatants and other aspects of the campaign against terrorism, but the Los Angeles decision was the first by a federal judge to strike down any portion of the Patriot Act.

"The critical thing here is that this is the first demonstration that courts will not allow Congress in the name of fighting terrorism to ignore our constitutional rights," said Nancy Chang, a senior attorney with the Center for Constitutional Rights, the New York-based organization that brought the lawsuit against the Justice Department on behalf of the humanitarian groups. "By using a broad and vague definition of terrorism, that has a chilling effect on free speech."

The Justice Department, which had already sought a review of last month's related decision, plans to review Collins' decision as well to determine whether it should be appealed, officials said.

Administration officials have made clear that they consider the act to be an integral part of their efforts to identify, track and disrupt terrorist activities.

Indeed, President Bush in his State of the Union address last week urged Congress to renew those parts of the act that are scheduled to expire in 2005. But the administration may face a tough sell in Congress, with a growing number of lawmakers from both parties questioning whether the government's expanded powers in dozens of areas of law enforcement have infringed on civil liberties. In largely symbolic votes, more than 230 communities nationwide have raised formal objections to the law.

Mark Corallo, a spokesman for the Justice Department, said in a statement Monday that the language banning "expert advice or assistance" to terrorists represented only "a modest enhancement" of previous law.

"By targeting those who provide material support by providing expert advice or assistance," he said, "the law made clear that Americans are threatened as much by the person who teaches a terrorist to build a bomb as by the one who pushes the button."