The District has invested $23,000 in new technology that it hopes will help settle debates over an issue that has inflamed passions among city residents: whether to cut down decaying trees.

Ainsley Caldwell, the District's chief forester, used the new device for the first time last Friday in Barnaby Woods, where Pepco had undertaken an aggressive pruning program to prevent trees from toppling onto power lines during storms.

While officials are still analyzing the results, they tout the device -- the Tree Radar Unit -- as a way to measure decay without cutting into the trees. And they say that they expect to use the machine to assess the health of trees in other District neighborhoods.

"It's like an X-ray," Caldwell said. "It can figure out the ratio of decay to solid wood."

Barnaby Woods residents became infuriated in September after discovering that Pepco was poised to cut down five to seven trees that it had identified as potentially hazardous to the electrical lines.

Their complaints prompted the city's Department of Transportation, which oversees trees on public land, to order a 90-day moratorium on the pruning so that arborists could inspect trees in the area.

In addition to Caldwell, who analyzed the trees for the city, arborist Keith Pitchford was hired by residents to conduct his own tests. Pitchford used a Resistograph, which measures a tree's density by drilling a tiny hole. Although his findings are preliminary, Pitchford found that one of five trees he examined, a Scarlet Oak, would likely be a "removal candidate."

"The other ones had some wounds, but they're superficial," Pitchford said. "I doubt they'll prove to be hazardous."

Pepco expanded its tree-cutting policy after Hurricane Isabel last year caused hundreds of trees to topple over power lines and left thousands of residents in the District and Maryland without electricity.

Bob Dobkin, a Pepco spokesman, said the utility is evaluating 50 power lines in the region to ensure that they won't be knocked out by falling trees. A feeder line in Barnaby Woods is among 10 under review in the District; others include lines in Shepherd Park, University Heights, Friendship Heights, Palisades and Foxhall.

The utility has increased its tree trimming budget from $8 million to $10.3 million.

"The trees are the biggest cause of outages during storms," Dobkin said, estimating that they account for 80 percent of power failures. "When the crews show up, we always have a few customers who come out and ask us not to touch the trees. It's something we have to do if we're going to provide reliable power."

In Barnaby Woods, residents in September discovered a Pepco crew preparing to remove trees along Barnaby Street. Their prodding prompted the city and Pepco to delay the work until further evaluation.

Barbara Gray, a 26-year resident of the neighborhood, said she is more concerned about preserving trees than enduring an occasional night without electricity.

"I don't care about the power outages," she said. "I'm used to it. I have a flashlight. I don't want to sacrifice these beautiful trees for 100 percent power."

The District purchased its new Tree Radar Unit from a Silver Spring manufacturer about a month ago. The device is half the width of a shoe box, weighs about three pounds and is hooked up to a laptop computer.

To use the machine in Barnaby Woods, Pepco had to turn off power to the neighborhood for four hours so that the electrical currents wouldn't interfere with its radio waves.

Michelle Pourciau, deputy director for the D.C. Division of Transportation, said the device may become useful in other neighborhoods if residents object to removing trees.

"When there's a question from an arborist over the right procedure, we can expect [to use] this," she said. "Where there are questions about the best action to take, our goal is to preserve and save every tree."