Nineteen men have been indicted on federal racketeering charges in the most aggressive legal assault in the Washington region on a Latino street gang believed by police to be responsible for a growing list of violent crimes.

It is the first racketeering case brought in Maryland against Mara Salvatrucha, also known as MS-13, and the latest sign of increased federal involvement in the effort to combat gangs.

The sweeping indictment -- and the resources devoted to obtaining it -- reflect the level of alarm over a group that was little known outside law enforcement circles and the neighborhoods in which it operates as recently as five years ago.

The indictment accuses the 19 alleged MS-13 members of six murders and four attempted murders in suburban Maryland between April 2003 and June 14. Nine of the 10 attacks occurred in Prince George's County; one was in Montgomery County. It also says the defendants conspired to commit kidnapping, robbery and obstruction of justice.

It ascribes a greater level of sophistication and structure to MS-13 than authorities had previously alleged.

According to the indictment, leaders of MS-13 factions from across the United States meet in person and communicate on cell phones to discuss rules and activities. Dues paid at meetings are passed along to support members in prison in the United States and in El Salvador. And members are required to commit acts of violence to stay in good standing.

Among the local cliques that belong to MS-13 are the Sailors Locos Salvatruchos Westside, the Teclas Locos Salvatruchos and the Langley Park Salvatruchos, the indictment says.

Flanked by law enforcement officials from Maryland and Northern Virginia at the federal courthouse in Greenbelt yesterday, Maryland U.S. Attorney Rod J. Rosenstein said during a news conference yesterday that MS-13 members "are in danger of going to federal prison for the rest of their lives." Federal racketeering carries a maximum penalty of life in prison, and there is no parole in the federal criminal justice system.

Prince George's State's Attorney Glenn F. Ivey, whose office has obtained convictions against several alleged MS-13 members for murder and assaults, said, "The key is the federal prosecutors are viewed as the sledgehammer as opposed to our hammer."

Rosenstein said agents from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives, U.S. Immigration and Customs Enforcement and local police officers -- 320 law enforcers in all -- fanned out at 1:30 a.m. yesterday to arrest nine of the suspects. The rest were already in custody on state charges.

The investigation was conducted by the Regional Anti-Gang Enforcement Task Force, which includes federal, local and state law enforcement agencies.

Rosenstein and other officials would not detail which suspect is tied to which crime. Rosenstein also deflected questions about what investigators have learned about the structure and leadership of MS-13. Such details will be revealed in court, he said.

Immigration officials will be notified of any defendants who are suspected of being in the country illegally, he said.

Relatives of most of the defendants could not be reached yesterday. But the father of one said that his son is a construction worker and is not in a gang.

Franklin Mejia Molina, also believed to be known as "Dragon," has worked at a construction site at Dulles International Airport for the past two weeks, said his father, who spoke on the condition that his name not be published.

"Maybe he has friends in a gang. There is a lot of confusion now," the father said.

The father said law enforcement agents stormed into his Silver Spring home during the early morning hours yesterday to arrest his son.

"I want to know what my rights are," he said. "They broke down the front door and put guns to the heads of my children, who are 8 years old and 7 years old." He said he brought his family to the United States from El Salvador in 2001.

Made up primarily of Salvadoran immigrants and other Central Americans and some Mexicans, Mara Salvatrucha was formed in the 1980s in Los Angeles, officials have said. Central American immigrants initially formed the group to protect themselves against older, well-established Mexican gangs.

Mara Salvatrucha began showing up in the D.C. area in the late 1980s.

In recent months, MS-13 has been accused of a series of high-profile attacks in Prince George's and Montgomery and in Northern Virginia. The gang is responsible for more than 20 homicides and dozens of attacks in the Washington area, authorities said. Virtually all the victims have been Latinos.

In Montgomery, two knife attacks in Colesville and Wheaton on Aug. 5 left six teenagers wounded; officials said the attacks were a two-pronged assault by MS-13 on a rival group. A dozen young men and teenagers are charged in those attacks, officials said. Two of the 19 defendants named in the racketeering indictment, Nelson Bernal, 24, of Hyattsville and Santos Maximos Garcia, 28, of Silver Spring, are each charged in one of the Montgomery knife attacks.

In Northern Virginia, where MS-13 emerged in the early 1990s, officials have increasingly turned to federal prosecutions to try to stymie the gang. In December, a federal grand jury in Alexandria indicted two alleged MS-13 members on racketeering charges. The case has not gone to trial yet.

In May, a federal jury in Alexandria convicted two MS-13 members in the murder of a teenager who became a witness against the gang.

The Prince George's state's attorney's office has prosecuted several MS-13 members for homicides and assaults in recent years. In January, a Prince George's jury convicted MS-13 gang member Mario Ayala of first-degree murder in the May 2004 beating death of Ashley Urias, 38, at a Suitland cemetery.

A co-defendant pleaded guilty to second-degree murder, and a third alleged accomplice, Everec Alvarez-Chacon, is scheduled to go on trial Sept. 19 on a charge of first-degree murder. Alvarez-Chacon is one of the purported gang members named in yesterday's indictment, and the Urias murder is one of the criminal acts the indictment alleges.

In April, a senior FBI official told a congressional committee that the agency has raised the priority of gang intelligence and investigative efforts.

The FBI will use "the same statutes and intelligence and investigative techniques previously used against organized crime against violent gangs," Chris Swecker, the FBI's assistant director/criminal investigative division, told a subcommittee of the House International Relations Committee.

The federal racketeering statute, known as the RICO law, was enacted by Congress in 1970 to give law enforcement a powerful tool to go after the Mafia, said Michael Greenberger, a professor at the University of Maryland School of Law and a former Justice Department official.

The law "was designed to allow you to get at people who were technically trying to keep their hands clean but were directing the criminal activity," Greenberger said. "You build the case by bringing in the criminal participants and the people who managed them."

According to the Justice Department's Criminal Division, about one-third of U.S. attorney's offices filed criminal charges under the RICO statute in 2003 and 2004.

Staff writers Fulvio Cativo, Joshua Partlow and Eric Rich and staff researcher Bobbye Pratt contributed to this report.

With Maryland U.S. Attorney Rod J. Rosenstein, left, Prince George's State's Attorney Glenn F. Ivey discusses the case.