New York ? The rapid spread of vicious street gangs such as MS-13 is causing alarm in cities and suburbs nationwide, igniting bitter debate about how best to combat the threat and inspiring a comprehensive anti-gang bill in Congress.

The measure is depicted by supporters as the only effective way to counterattack gang violence, and assailed by critics as an overreaction that could clog both federal courts and adult prisons with youthful offenders.

Sponsored by Rep. Randy Forbes, R-Va., the bill moved swiftly through the House Judiciary Committee last month and is scheduled for a House floor vote Wednesday. It would turn many gang-related violent offenses into federal crimes punishable by mandatory sentences of at least 10 years, expand the range of crimes punishable by death, and enable U.S. prosecutors to try 16- and 17-year-old gang members as adults in federal courts.

“These aren’t petty hoodlums,” Forbes said. “They’re cutting people’s heads off, doing countersurveillance on police. … They’re trained in a type of violence we’ve not seen heretofore.”

The bill’s supporters include the National Sheriffs’ Assn. and the Fraternal Order of Police, the nation’s largest law enforcement union. If approved, it would move to the Senate where Sens. Dianne Feinstein, D-Calif., and Orrin Hatch, R-Utah, have introduced a bill combining tough anti-gang measures with new funding for crime prevention programs.

Opponents include numerous high-powered civil rights groups — the NAACP, the American Civil Liberties Union, Human Rights Watch and others. They cite FBI findings that serious youth crime is declining, say states can best address the problem and worry about long-term consequences for teenage offenders sent to adult prisons.

Critics of the bill say state and local police agencies could escalate the fight against such gangs under existing laws. They also say the Bush administration and Congress have cut back social programs that could deter youths from joining gangs in the first place.