IT WAS AN exceptionally revolting, vicious assault along Edsall Road in the Alexandria area of Fairfax County about 1 a.m. Monday: A 16-year-old boy's hands were hacked with a machete -- severing four fingers on one hand -- during an attack allegedly by members of a rival gang. But as many authorities know, and not enough residents across this region realize, this was no isolated instance of brutality. Police note that the victim and assailants are members of rival gangs, one of which has been linked to at least five killings in Northern Virginia, as well as shootings, other machete attacks, baseball-bat beatings, stabbings and sexual assaults. The gang violence is spreading swiftly, according to federal and local officials, into Maryland and the District.

In a report to Attorney General John D. Ashcroft in February, Paul J. McNulty, U.S. Attorney for the Eastern District of Virginia, reported that gang activity is "a serious and growing problem" in Northern Virginia. Fairfax County police have documented more than 200 gangs in Northern Virginia over the past seven years; of these, he says, "some 80 gangs exist in Fairfax County on any given day." Local law enforcement officials estimate that more than 2,700 individuals are associated with gangs. Police said Monday's attackers are believed to be members of the largest group, with a propensity for violence: Mara Salvatrucha, or MS-13. Another "gang of immediate concern," Mr. McNulty reported, is the South Side Locos, of which the victim was a member.

In Fairfax County, police reported more than 700 gang-related incidents in 2003, Mr. McNulty notes, including 275 graffiti complaints to 55 assaults, 37 malicious wounding incidents, 10 assaults by mob, 16 drug-related charges, 13 robberies, seven rapes and 11 stolen vehicles. Gang members range in age from 11 to 40; forceful recruiting is being done in middle schools.

Rep. Frank R. Wolf (R-Va.) for years has been urging increased anti-gang efforts, such as outreach task forces of law enforcement and school authorities. He is seeking more federal funds to beef up federal, state and local efforts. Gang activities are not confined to narrow turfs; they are raising hell in shopping malls and other gathering places. Authorities say they expect the violence to increase and spill across jurisdictional boundaries. In response, officials of the region need to step up their cooperative efforts.