EASTERN NECK NATIONAL WILDLIFE REFUGE, Md. – Eleven-year-old Robert Bennington stood in the midday heat, studying the global positioning system device in his hand. Eyeing a vine of “mile-a-minute” weed climbing 6 feet high on a nearby tree, the fifth-grader was plugging the growth’s location into the mapping system so managers of the refuge could track its progress.

Bennington played down his expertise, saying he was “not really” an expert at the satellite-based navigation technology, but the Chestertown, Md., youth knew more about it than most of the adults standing by. “Since I usually walk these trails, I’d like to be able to walk straight into these woods and have cool things to fiddle with, cool GPS things,” he said.

Gathered on this 2,300-acre island in Chesapeake Bay in mid-July, Bennington and nearly 20 other volunteers represent a new front in the fight against invasive species. After years of relative inaction, federal authorities and private citizens are mobilizing to curb the spread of non-native plants and animals in the United States.

“Invasive species are the greatest environmental threat of the 21st century, bar none,” said Tom Stohlgren, an ecologist at the U.S. Geological Survey’s Institute of Invasive Species Science, who ranks it a greater problem than global climate change.

Although exotic species have been infiltrating the Americas at least as far back as 1492 – when Christopher Columbus landed in the Bahamas with European wheat, barley and rye – global travel and trade have helped them proliferate in recent decades. From zebra mussels to the vibrant purple loosestrife plant, these species outcompete many native inhabitants, degrade habitat and drive some to extinction. Scientists like to compare them to the villain in the 1951 sci-fi flick “The Thing,” which consumed everything in its path.

“We pay for these organisms, whether we combat them or ignore them,” said Richard Mack, an ecologist at Washington State University. “We simply can’t afford, as a nation, to wait before we take action against these species.”

Invasives are a worldwide problem as well, and some countries, such as Australia and New Zealand, are taking stringent action. In some instances, native American species, such as rainbow trout, have moved overseas.

It is difficult to calculate the precise damage invasives inflict, but Cornell University’s David Pimentel estimates there are 50,000 plants and animals that came from somewhere else, costing the United States more than $125 billion a year by sparking fires, blocking waterways and destroying crops. For instance, zebra mussels, which infiltrated the Great Lakes in the mid-1980s and clog pipes in power plants and other facilities, cost that region $100 million to $200 million a year, said David M. Lodge of Notre Dame University.

Along with the Great Lakes and San Francisco Bay, Chesapeake Bay has emerged as a “hot spot” for non-native species, Lodge said, because of the busy port of Baltimore. Ships bring in exotic plants and animals on board as commercial imports, and also discharge invasive marine organisms through ballast water.

Rachel Cliche, a biologist who works at Eastern Neck and three other national wildlife refuges in Maryland, said that when she arrived in September 2004 to study and control exotic species, “it was overwhelming, because there were so many invasives.”

In addition to mile-a-minute weed, an import from Asia that grows 6 inches a day and displaces any plant in its way, Cliche and her colleagues at the refuge are battling Japanese honeysuckle, multiflora rose and mute swans from Europe, which eat 8 pounds in aquatic vegetation a day. All deprive the refuge’s native waterfowl – it is a sanctuary for more than 240 kinds of birds – of food and habitat.

Eastern Neck is not alone. The Fish and Wildlife Service, which oversees wildlife refuges, estimates that invasives have degraded 10 percent of the 545 refuge habitats, covering 8 million acres. In December 2002, an internal survey of wildlife refuge managers identified non-native species as the system’s No. 1 threat.

“The problem is we just didn’t know the full extent of invasives on refuges,” said Evan Hirsche, president of the National Wildlife Refuge Association, a nonprofit that lobbies on the refuges’ behalf. “And invasive species clearly don’t stop at the refuges’ borders. They’re a threat to all conservation lands in this country.”

For the first time, federal officials are launching a serious effort to chart non-native species nationwide. The task is particularly daunting because the refuges face budget shortfalls: The system gets $4 per managed acre from the federal government, compared with $20 per acre the National Park Service receives.

Last year, refuge officials, in concert with The Nature Conservancy and the National Wildlife Refuge Association, used $1 million in federal funds to map where invasives have spread on six refuges. Now, with another $1 million from the government, they are charting an additional seven, including Eastern Neck. Better tracking will allow each refuge to determine how best to get rid of invasives, officials said, by chemical, mechanical or biological means.

“We’re looking at every square foot. It’s very intense mapping,” said Kathy Huffman, a Fish and Wildlife Service biologist who has tracked invasives at Ohio’s Ottawa National Wildlife Refuge.

Refuge officials are sharing their results with scientists at the U.S. Geological Survey and NASA who are assembling a national database on non-native species.

“For terrorists, we would have done this,” Stohlgren said. “We would figure out how they’re coming in and where they’ll go.”

Although the federal government is beginning to respond, several experts said the nation has not focused enough money and attention on the problem. The Geological Survey is spending $12 million, or a little over 1 percent of its budget, on non-native organisms this fiscal year, and other agencies spend a similar portion of their funds.

“We are not dealing with it adequately,” said John M. Randall, who directs The Nature Conservancy’s invasive-species initiative.

Hoping to influence the private sector as well, Randall has worked with such retailers as Lowe’s Home Improvement Warehouses to curb the sale of exotic species. Last fall, Lowe’s stopped selling 45 invasive plants in its Florida stores after consulting with nursery growers and environmental groups.

“It’s the right thing to do,” said Michael Chenard, the chain’s director of environmental affairs.

Washington Post researcher Meg Smith contributed to this report.