LOS ANGELES — A federal appeals court ruled yesterday that some portions of the U.S. Patriot Act dealing with foreign terrorist organizations are unconstitutional because the language is too vague to be understood by a person of average intelligence.

The ruling by the 9th U.S. Circuit Court of Appeals in San Francisco affirms a 2005 decision by U.S. District Judge Audrey Collins, who ruled on a petition seeking to clear the way for U.S. groups and individuals to assist political organizations in Turkey and Sri Lanka.

Collins said language in the Patriot Act was vague on matters involving training, expert advice or assistance, personnel and service to foreign terrorist organizations. Her ruling prevented the federal government from enforcing those provisions as they apply to the terrorist groups named in the lawsuit.

The language of the law is so unclear, plaintiffs argued, that it could be used to prosecute people who trained members of foreign groups in "how to use humanitarian and international law to peacefully resolve ongoing disputes" or in how to ask the United Nations for disaster relief. Violators could be subject to prison terms of up to 15 years.

Charles Miller, a Justice Department spokesman, said his agency was reviewing the ruling to determine a response.

In its 27-page decision in Humanitarian Law Project v. Mukasey, the unanimous three-judge panel said that to survive a vagueness challenge, a statute "must be sufficiently clear to put a person of ordinary intelligence on notice that his or her contemplated conduct is unlawful."

The language covered by the ruling remained unconstitutionally vague despite congressional amendments to the Patriot Act meant to remedy the problems, the appeals court ruled.