On a sweltering afternoon, an unmarked white jetliner taxies to a remote terminal at the international airport here and disgorges dozens of criminal deportees from the United States. Marshals release the handcuffed prisoners, who shuffle into a processing room.

Of the 70 passengers, at least four are members of Mara Salvatrucha, or MS-13, a gang formed two decades ago near MacArthur Park west of the Los Angeles skyline.

For one of them, Melvin "Joker" Cruz-Mendoza, the trip is nothing new. This is his fourth deportation -- the second this year.

Wiry with a shaved head, the 24-year-old pleaded guilty in separate felony robbery and drug cases in Los Angeles. "MS" covers his right forearm. Other tattoos are carved into the skin above his eyebrows.

In the last 12 years, U.S. immigration authorities have logged more than 50,000 deportations of immigrants with criminal records to Central America, including untold numbers of gang members like Cruz-Mendoza.

But a deportation policy aimed in part at breaking up a Los Angeles street gang has backfired and helped spread it across Central America and back into other parts of the United States. Newly organized cells in El Salvador have returned to establish strongholds in metropolitan Washington, D.C., and other U.S. cities. Prisons in El Salvador have become nerve centers, authorities say, where deported leaders from Los Angeles communicate with gang cliques across the United States.

A gang that once numbered a few thousand and was involved in street violence and turf battles has morphed into an international network with as many as 50,000 members, the most hard-core engaging in extortion, immigrant smuggling and racketeering. In the last year, the federal government has brought racketeering cases against MS-13 members in Long Island, N.Y., and southern Maryland.

Across the country, more than 700 MS-13 members have been arrested this year under a new enforcement campaign that U.S. immigration authorities say will lead to more serious cases and longer sentences for gang members before they are deported.

"Ultimately, our job here is to enforce the immigration laws and then remove [criminal gang members] from the country," said John P. Torres, the acting director overseeing detention and removals for the Department of Homeland Security's Immigration and Customs Enforcement agency. But for a sizable number of MS-13 members, deportation is little more than a taxpayer-financed visit with friends and family before returning north.

"I think most of the police departments will agree that you're just getting them off the street for a couple of months," said FBI Assistant Director Chris Swecker, who is coordinating investigations across North America, where the gang operates in a loose network of cells.

Deportations have helped create an "unending chain" of gang members moving between the U.S. and Central America, said Rodrigo Avila, El Salvador's vice minister of security.

"It's a merry-go-round."

Turnaround in El Salvador

Cruz-Mendoza has been riding the merry-go-round for eight years.

He was a minor when he was deported in 1997 and again in 1998, federal immigration officials said.

In December 2003, he was convicted of attempted robbery, after he shoved a woman into a fence while trying to steal her purse at a South Los Angeles bus stop, court records show. As he demanded money, she said, he made threatening gestures and reached into his pocket, where police found a six-inch steak knife when he was arrested shortly thereafter.

In March 2004, he pleaded guilty to a second felony of drug possession, which was dismissed in a sentencing deal for the attempted robbery.

After serving little more than a year in jail, Cruz-Mendoza was deported for a third time in January, records and interviews show.

U.S. Border Patrol agents arrested him in Arizona a month later. At that point, he could have been charged with a felony for reentering the country after deportation, which could have landed him in federal prison for as long as 20 years.