The two fastest-growing and most powerful gangs in the world are homegrown products of Los Angeles. The Mara Salvatrucha gang, or MS-13, and the 18th Street gang, known in Central America as Mara 18, sprang up in Pico-Union and the densely populated neighborhoods around MacArthur Park. But unlike many local street gangs, these two were entrepreneurial: They recruited Central American immigrants across the city and then expanded farther -- throughout Mexico, El Salvador, Guatemala and Honduras. Conservative estimates put MS-13's ranks at 20,000 and 18th Street's at 30,000 worldwide.

Stopping street gangs is no longer a local matter -- a point driven home to me during a symposium in El Salvador. During the conference, two points of consensus emerged. First, MS-13 and 18th Street have become an international concern -- indeed, even Interpol is now involved in the fight. Second, past strategies to handle these gangs have failed.

In the 1990s, the U.S. strategy centered on deportation: Undocumented gang members convicted of crimes were sent back to their country of origin after their prison sentences. But this only exacerbated the problem, spreading both gangs like a virus until they grew into transnational "super-gangs" with countless cliques in southern Mexico and Central America in addition to their presence in California, Nebraska, New York, Texas, Virginia, Oregon and even Canada.

The FBI now acknowledges that the MS-13 and 18th Street gangs have become America's new organized crime, using their numerical superiority and sheer muscle to extort "rent" or "taxes" from local businesses, including legal and illegal vendors. These "protection" rackets are an insidious form of crime, often going undetected because the victims are unwilling to come forward lest they incur the gangs' wrath; they also supply the gangs with steady profits and fuel their growth.

Much of what I learned in El Salvador was cause for alarm, but there was also reason for hope.

First, the good news. El Salvador's partnerships with U.S. law enforcement agencies are producing results. Intelligence on the super-gangs now flows between the U.S. and El Salvador. U.S.-sponsored initiatives on fingerprinting, police training and the handling of criminal deportees are working, and they provide a model for other countries.

El Salvador's political leadership appears committed to expanding the country's gang prevention and intervention programs. This is crucial, because effective gang reduction requires more than just arrests and gang sweeps. We must be tough on gangs but equally tough on the social conditions that breed them.

Now, the bad news. Despite progress, both super-gangs are still growing in influence across the hemisphere. Five years ago, Mexico reported little MS-13 presence; today, MS-13 is the dominant gang in Mexico's southern states. In Central America, the super-gangs are branching out beyond extortion into drug trafficking, human trafficking, identity theft and fraud. Sadly, we can expect to see similar expansion in the United States.

Nevertheless, U.S. law enforcement officials can succeed if we build on the following principles.

First, gangs fight over turf. Those of us battling them must not. Whether it is politicians arguing over control or bureaucrats wrestling over resources, infighting does not serve the public interest. Federal, state and local authorities must coordinate their efforts. This year, prosecutors in my office and the U.S. attorney's office, working together for the first time, coordinated efforts to good effect. Federal prosecutors filed criminal indictments against gang members in South Los Angeles and Glassell Park, while city prosecutors filed nuisance-abatement lawsuits to shut down the gangs' headquarters and hangouts.

Second, super-gangs observe no jurisdictional boundaries, so law enforcement officials in the U.S. need to expand international partnerships to stop the gangs' growth. The Los Angeles Police Department's new officer-exchange program with the El Salvador police is a good start, but there's still a long way to go in developing genuine working relationships with the rest of Central America.

Finally, gangs evolve. So must our methods and our laws. This year, for instance, I sponsored statewide legislation, which the governor recently signed into law, to allow prosecutors to sue gang members in civil court for damages. Now gang leaders, or "shot callers," can be held accountable for the full spectrum of damage their foot soldiers cause -- from graffiti vandalism to the costs associated with violent crime. This tool should prove particularly effective against gang leaders who direct criminal activities from behind bars, a problem Sheriff Lee Baca and Police Chief William J. Bratton have discussed in recent months.

For too long, Los Angeles has thought of street gangs as a local crisis. But the problems they present are bigger than that, and if the city wants to save countless young men and women from gang life, the solutions will have to be bigger too.

Rocky Delgadillo, the Los Angeles city attorney, oversees the enforcement of 57 gang injunctions, including ones against the MS-13 and 18th Street gangs.