A federal judge dismissed criminal charges Wednesday against the environmental group Greenpeace, ending an unusual case that drew the ire of free-speech advocates and critics of the Bush administration.

The activist group, known for its high-profile demonstrations, was criminally charged after two members were caught in April 2002 boarding a ship off Miami Beach that they believed was carrying 70 tons of illegally imported Brazilian mahogany.

The activists spent a weekend in jail. But the case became a national cause celebre when the U.S. attorney's office here took the unprecedented step of seeking a criminal indictment of the organization itself, using an obscure 1872 law intended to dissuade brothel owners from boarding ships to lure sailors with prostitutes and liquor. The law had not been used in 113 years.

Greenpeace's attorneys did not have to offer up evidence to counter the charges on Wednesday because U.S. District Judge Adalberto Jordan in Miami dismissed the case shortly after the prosecution presented its last witness following 11/2 days of testimony.

"The Bush administration and its allies are bent on chilling dissent," said John Passacantando, Greenpeace's executive director. "This is clearly a big victory for America's tradition of free speech."

Scott Anderson, a third-grade teacher from Moab, Utah, who was one of the two activists arrested in connection with boarding the cargo ship in 2002, said, "The checks and balances system worked. The message is: You cannot pick on advocacy groups."

Carlos B. Castillo, a spokesman for U.S. Attorney Marcos Daniel Jimenez, said the verdict would not alter the office's approach to handling protest cases.

"The U.S. attorney's office remains undeterred in prosecuting those persons who illegally attempt to board ships at the Port of Miami or otherwise threaten port security," he said.