A federal judge has withdrawn a highly publicized ruling she issued last year declaring that President Bush acted unconstitutionally when he designated 27 groups and individuals as terrorists in 2001.

Reconsidering the issue at the government’s request, Judge Audrey Collins of Los Angeles concluded that American supporters of Kurdish and Tamil separatist groups lack standing to challenge the terrorist designations, which applied to Osama bin Laden, Al Qaeda, and others linked to militant Islam.

“Plaintiffs have pointed to no instance of their being issued a specific threat or warning that … they would be designated,” the judge wrote in a 16-page order Friday. “Plaintiffs’ fear of designation is ultimately based on speculation. Accordingly, plaintiffs cannot establish a genuine and immediate threat that they will be designated by the President.”

In November, Judge Collins ruled that Mr. Bush’s designations were “unconstitutionally vague” because he set forth no criteria for inclusion on the list and established no mechanism to get off of it. A terrorist designation typically freezes all assets in America belonging to a group or individual. Americans are also barred from doing business with or providing aid to those on such lists.

The judge’s about-face was quickly seized upon by the Justice Department, which filed a copy of the decision Monday with a Texas judge handling a case against leaders of an alleged Hamas front, the Holy Land Foundation for Relief and Development.

Judge Collins left open the possibility that groups or individuals with close ties to the 27 entities on the September 2001 list could mount a new challenge to the designations.

“She has not said, ‘I’ve determined it’s constitutional,'” a lawyer for the plaintiffs, David Cole, said. An appeal is planned, he said.

Judge Collins also ruled that the government successfully cured a constitutional problem stemming from language in Mr. Bush’s order that permitted freezing the assets of those “otherwise associated with” designated terrorist entities. In January, the Treasury Department issued regulations that define that relationship to mean owning or controlling a terrorist entity, or providing “financial, material or technological support, or financial or other services” to such a group.

The plaintiffs claim the definitions are still too vague, particularly catchall terms such as “other services.” However, Judge Collins said the new definition made what was prohibited clear enough.

The lawsuit was brought by the New York-based Center for Constitutional Rights on behalf of groups and individuals who said they wanted to support nonviolent activities of two groups on a State Department terrorism list, the Tamil Tigers and the Kurdistan Workers’ Party, known as the PKK.

Mr. Cole, a law professor at Georgetown University, said the statute invoked by the president’s order, the International Emergency Economic Powers Act of 1977, gives him t too much authority. “It’s very much like the blacklists of the McCarthy period. The president can designate anybody he wants for any reason, or no reason at all,” Mr. Cole said.

In her new ruling, the judge lifted earlier injunctions against applying parts of Mr. Bush’s order to the parties that brought the lawsuit. Despite the sweeping implications of her previous decision, she never blocked the executive order’s application to Al Qaeda and others not directly involved in the litigation.

Judge Collins, an appointee of President Clinton, has issued a series of decisions curtailing the federal government’s authority in terrorism cases. In 1999, she ruled that a criminal law banning the provision of “personnel” or “training” to terrorist groups was unconstitutionally vague. In 2003, she ruled that a ban on “expert advice and assistance” to terrorist groups contained in the USA Patriot Act was also void for vagueness.