San Diego ? A sabotage campaign by the nation’s most radical environmental group has moved from the countryside to the doorstep of the nation’s biggest cities.

The Earth Liberation Front, a movement that originated in the forests of the Pacific Northwest, has claimed responsibility for a string of arsons in the suburbs of Los Angeles, Detroit, San Diego and Philadelphia in the past 12 months. No one has been charged in any of the attacks.

The attacks, which included the costliest act of environmental sabotage in U.S. history, have targeted luxury homes and SUVs, the suburban status symbols that some environmentalists regard as despoilers of the Earth.

“Their actions used to be aimed at ‘out in the country’ industries,” said Ron Arnold of the Bellevue, Wash.-based Center for the Defense of Free Enterprise, who has written several books criticizing the environmental movement’s radical wing. “Now they’re moving from a save-the-wilderness focus to an anti-capitalist focus.”

This summer, environmentalists in Southern California turned six-figure luxury homes under construction into charred sticks of wood, destroyed an unfinished 206-unit apartment complex and firebombed brand-new Hummers, the mammoth sport-utility vehicles that start at $50,000.

The ELF is the FBI’s No. 1 domestic terrorism priority. The organization has done more than $100 million damage — but caused no deaths — since it split off from the radical environmental group Earth First! and surfaced five years ago in the United States.

The ELF first took aim at urban sprawl in 2000, when it burned luxury homes and condos under construction on New York’s Long Island. But Phil Celestini, the agent in charge of the FBI’s domestic terrorism operations unit in Washington, noted that the San Diego fires “are taking places in more densely populated areas than in the past.”

On Aug. 1, a fire destroyed a five-story, 206-unit apartment complex under construction in San Diego’s University City neighborhood.

The damage estimate of $50 million made it “the single largest act of property destruction ever committed by one of these groups in the history of the country,” Celestini said. “It’s sheer dumb luck and providence that someone has not been killed. You set a fire that big, there’s no way of predicting what the ultimate consequences will be.”

A contractor walks through Clippinger Chevrolet in West Covina, Calif., where vandals torched and vandalized sport utility vehicles the previous day. The radical Earth Liberation Front stated in an unsigned e-mail that the Aug. 12 incidents were ELF