The past several months have residents of Lawrence, Mass. frightened by one of the most difficult crimes to prove: arson.

The fire department has arranged arson statistics from the past year into a graph which shows that an overwhelming 131 cases of arson have occured since January. Twenty-two were reported in September alone, says Lieutenant John P. Burton of the Arson Squad.

"I stopped counting in May, myself," says Burton.

A spokesperson in the mayor's office confirmed that last week, members of the National Guard arrived at the town of 70,000 to offer assistance. The guards were unavailable for comment.

Most of the buildings targeted are abandoned 2-to-3 story homes in the northwest section of the city, Burton says. He said the fire department be-lieves that the burned-out dwellings may be the work of competitive drug dealers, their vengeful customers, or high school kids looking for entertainment on a Saturday night.

Since the vacant houses frequently serve as the base of operations for drug dealers, arson might be a way to reduce the competition "if one particular house is doing better than another," Burton Says. If the drugs are bad, then buyers might set fire to the place of purchase to "teach [the dealers] a lesson," he says. Or, the arsonists might be young people setting fires "for kicks," he says.

A "chain reaction" may have been set off, Burton says, once the town started getting publicity for its rash of arson cases. "Some of the street gangs are talking, and other street gangs say, 'we can do a better one,''' Burton says.

Yet the fire department hopes to put out the flames once and for all with some support from the National Guard, the Massachusetts State Police Fire Marshal's office and Federal agents in the Alcohol, Tobacco and Firearms branch of the FBI.

"With extra help, we're going to put a damper on it," Burton says.