The government can prosecute private citizens for giving advice to a foreign organization - on how to negotiate peace or take its case to the United Nations, for example - if the group is on the U.S. terrorist list, the Supreme Court ruled Monday.

In the most important foreign policy and civil liberties case of their 2009-10 term, the justices ruled 6-3 that a law prohibiting "material support" of foreign terrorist organizations can be used against people who claim to be providing only peaceful, humanitarian assistance.

Any tangible support - money, legal aid or political advice - "frees up other resources within the organization that may be put to violent ends," Chief Justice John Roberts said in the majority opinion.

"It also importantly helps lend legitimacy to foreign terrorist groups - legitimacy that makes it easier for those groups to persist, to recruit members, and to raise funds - all of which facilitate more terrorist attacks," Roberts said.

Dissenting Justice Stephen Breyer protested that the majority's interpretation "would deny First Amendment protection to the peaceful teaching of international human rights law," on the grounds that it might enable terrorists to conduct sham negotiations.

Those who intend to aid terrorism should be prosecuted, but any broader use of the law would violate free speech, argued Breyer, whose dissent was joined by Justices Ruth Bader Ginsburg and Sonia Sotomayor. The majority included liberal Justice John Paul Stevens as well as the court's conservatives - Roberts and Justices Antonin Scalia, Anthony Kennedy, Clarence Thomas and Samuel Alito.

Furious debate

The ruling touched off a furious debate over the government's power to prevent dissidents from helping blacklisted organizations. The ban on "material support" for foreign terrorists was signed into law by President Bill Clinton in 1996 and was expanded in the USA Patriot Act that President George W. Bush signed in 2001.

Under Monday's decision, "human rights advocates, providing training and assistance in the nonviolent resolution of disputes, can be prosecuted as terrorists," said David Cole, lawyer for organizations and individuals who challenged the law.

The plaintiffs sought to train members of two groups on the State Department's terrorist list - the Kurdish Workers Party in Turkey and the Liberation Tigers of Tamil Eelam in Sri Lanka - in peaceful conflict resolution and advocacy before the United Nations.

Those forms of assistance to such "deadly groups" could lead to prosecution, the court said Monday, while insisting it was not restricting free speech. "Plaintiffs may say anything they wish" on their own behalf, Roberts said.

Carter concerned

Civil liberties advocates said they also feared repercussions for U.S.-based critics of the Israeli government, who might be charged with aiding Hamas, which Washington has designated as a terrorist group. One such critic is former President Jimmy Carter, whose private Mideast diplomatic efforts have included contact with Hamas.

The ruling "threatens our work and the work of many other peacemaking organizations that must interact directly with groups that have engaged in violence," said Carter, whose organization filed arguments with the court.

On the other side, Annemarie McAvoy, a Fordham law professor and former federal prosecutor, said the court recognized the "reality factor" of a world in which groups such as al Qaeda thrive on aid funneled through charities.

"By helping the terrorists, even tangentially, they're freeing up the terrorists to focus on other things, such as violent attacks," McAvoy said.

During arguments in February, Solicitor General Elena Kagan, now President Obama's nominee to the court, defended the law and urged a broad interpretation that would allow prosecution of a U.S. citizen who filed a legal brief on behalf of a terrorist organization.

"What Congress decided," Kagan told the court, "is that when you help Hezbollah build homes, you are also helping Hezbollah build bombs."