The FBI was investigating whether a radical environmentalist organization was responsible for a fire ignited by explosives that destroyed two buildings and several vehicles at a tree nursery. 

The FBI was also looking into whether arson was to blame for a fire that gutted laboratories and offices at the University of Washington's Center for Urban Horticulture, about 150 miles to the north. 

Both fires were reported at about 3:20 a.m. Monday. No one was injured. 

"It's too early to say that those two things are connected," FBI agent Ray Lauer said. "If (the Seattle fire) turns out to be a politically motivated arson, then we're interested. Then we have to look to see if it's connected with anything else." 

In the Oregon fire, about a half-dozen pickups, all-terrain vehicles and a semitrailer at Jefferson Poplar Farms were destroyed along with an equipment storage building and a maintenance building, the Oregon State Police said. Jefferson grows hybrid trees for paper production. 

A number of undetonated explosives were found by arson investigators near the nursery's office building. Officials declined to describe the devices. 

The letters "ELF" were written on the side of a building, as was the phrase "You cannot control what is wild," said FBI spokeswoman Beth Anne Steele. 

The Earth Liberation Front is a shadowy group that, since 1996, has claimed responsibility for arson attacks against commercial entities that the radicals say threaten or damage the environment. 

On Monday afternoon, ELF spokesman Craig Rosebraugh said: "At this point, the ELF has not officially claimed responsibility. But I wouldn't be surprised if an official statement came out." Rosebraugh has said he is not an ELF member and only reports its activities. 

As of Monday night, similar graffiti had not been found at the horticulture center in Seattle, investigators said. The Bureau of Alcohol, Tobacco and Firearms was bringing a dog to sniff for evidence of accelerants. 

The fire destroyed decades of work and records for some teachers and researchers. 

"Rational people do not do this," said H.D. "Toby" Bradshaw, a professor at the urban horticulture center. "If it was a personal scientific dispute, we'd be debating this in a public forum." 

Bradshaw said previous owners of the Oregon tree nursery were affiliated with a university-based group called the Poplar Molecular Genetics Cooperative. 

A group calling itself the Washington Tree Improvement Association attacked Bradshaw's genetic engineering research by hacking down 200 trees on Nov. 27, 1999, three days before the World Trade Organization riots in the city's downtown area. 

On Monday, Bradshaw said, plastic boxes in which he keeps a pair of corn snakes for use in biology lectures were moved from his office to a place under a tree, far from the flames. That could indicate the fire was set by someone who broke into his office, he said. 

Tom Hinckley, the center's director, said he lost more than 30 years of teaching and research records, including slides documenting the regrowth of vegetation in the blast zone from the eruption of Mount St. Helens on May 18, 1980. 

The FBI considers the ELF one of the county's leading domestic terrorist organizations, with millions of dollars in damages linked to its actions since 1997. Steele said the Pacific Northwest is "ground zero for eco-terrorism." 

The ELF claimed responsibility for a 1998 fire that caused $12 million damage at the Vail, Colo., ski resort. The group said the fire was set because Vail had expanded into lynx habitat. The group also claimed responsibility for other fires including one Jan. 2 that caused $400,000 damage at Superior Lumber Co. in Glendale, Ore.