For many troubled youths, joining the armed services has provided an opportunity to master a skill, learn self-discipline and develop respect for authority.

But police are beginning to see signs that some street gang members may have different motives to join. In recent months, investigators in Arlington, Austin and San Antonio have arrested or documented the backgrounds of off-duty soldiers who they say are also active gang members.And in Killeen, home of Fort Hood, police say they regularly encounter soldiers who are members of local street gangs. A Fort Hood soldier affiliated with a street gang that originated in Los Angeles was sentenced to life in prison on July 19 for the drug-related shooting death of a man outside a Killeen apartment complex last year. The soldier, Pvt. Marvin Clair, was an Army computer programmer who is known on the street as "Koolaid" or "Kool," police said.

The implications of gang members receiving military training are frightening, police say. Police, already outgunned by gangs armed with rapid-firing automatic weapons, shudder at the idea of gang members skilled in detonating explosives and conducting surveillance operations.

"One of the things we are seeing is that young soldiers are being used as a tool to learn military systems and strategies and so forth," said John Chapman, an investigator with the Killeen Police Department. "And they're bringing that back into the gang environment for their form of urban guerrilla warfare."

Military investigators said they thoroughly check the backgrounds of recruits and doubt that many gang members could be entering their ranks. But military recruiters - and even law officers - have difficulty gaining access to juvenile records. As a result, many recruits with juvenile offenses slip into the military undetected.

"When we run local police checks, some agencies will release juvenile records and some do not," said Maj. John Napoli, executive officer of the Army's Dallas Recruiting Battalion. "Sometimes we get them and sometimes we don't."

A bill is being drafted for the upcoming session of the Texas Legislature by state Sen. Chris Harris and state Rep. Toby Goodman, both Arlington Republicans, that would make juvenile criminal records more accessible to police and military recruiters.

Police say gang members also get into the military simply because they have somehow managed to escape criminal charges during their years on the streets.

"They may have engaged in some of the criminal activity of the gang but never been caught," said Chapman, who investigates gangs in Killeen.

On Aug. 25 in Arlington, police documented that a member of one of the city's most criminally active gangs was an off-duty soldier from Fort Hood, the nation's largest Army base, said police Sgt. Bill Weatherly. Police often document individuals who claim gang membership by photographing them and recording their names and nicknames for intelligence purposes.

The 25-year-old soldier, who was going by the street name "Big Ace," was hanging out with the gang's "OG," or "Original Gangster," a slang term for the founding leader of a gang, Weatherly said. He had a large, horseshoe-shaped tattoo of the gang's initials across his stomach and told police he was in the Army's specialized long-range reconnaissance unit, Weatherly said.

"That is a little bit scary for us," said Weatherly, who heads the Arlington police gang unit, "because you think, `Man, this guy could be setting us up, watching us, doing anything he wants.' "

About a week later, on Sept. 3, Arlington police arrested six soldiers from Fort Riley, Kan., who had jumped a fence to avoid paying admission to Six Flags Over Texas. Five of the soldiers claimed membership in a gang in southern California. Some were armed with serrated, folding knives, Weatherly said.

The leader of the group, John A. Arroyo, 21, had a large tattoo on his arm with the initials "BTL," and said his street name is "Snowman." Weatherly said Arroyo professed his eagerness to get out of the Army, go back to his neighborhood and resume "gangbanging," a street term for an array of criminal activities.

The Fort Riley soldiers spent the night in Arlington Jail charged with theft of service, a Class C misdemeanor, and were released the next morning after paying fines, Weatherly said.

"They were on leave from Fort Riley, and they all popped military IDs out," he said. "You could tell real quick that these were hard-core gang members. There was no doubt in anybody's mind that they weren't scared of anybody out there."

Officials at Fort Riley declined to comment about the soldiers.