Brian and Burke want to be police officers. So do Matthew and Scott. But not all the teenagers who spent last week at Alexandria police headquarters were cadets in waiting.

They were among more than a dozen youngsters who devoted a week of their summer to the third Youth Citizens' Police Academy, a course held each August that offers teenagers an up-close, hands-on opportunity to find out how their police department works.

"I thought police only did one job--catch bad guys. I used to think they were mean," said Brian Powell, 14, who will be in ninth grade at Minnie Howard School.

"But the only time they have to be mean is when a person doesn't cooperate," he said. "I've seen they save lives, go off buildings, look in windows. When you're a K-9 officer, the dog is your best friend."

Brian and his academy mates saw all kinds of things they hadn't seen before. They visited the firing range and the communications center. They observed the polygraph and fingerprinting processes. They met with an officer who patrols on a bicycle and heard from a sergeant who negotiates with hostage-takers.

They visited the city courthouse in Old Town and the home of a residential police officer in a public housing complex in Del Ray. They watched K-9 teams go through precision maneuvers with the dogs and saw members of the special operations team rappel off the roof of the jail.

"The academy can help the kids relate to the police better," said Officer Charlette Young, the police department's Drug Abuse Resistance Education instructor, who runs the class with a mix of informality and authority. "They see that we're human. They interact with other officers without them slapping the handcuffs on."

Sgt. Ron Ware, supervisor of the crime prevention unit, told the students: "There are a lot of misconceptions about the police department and about you. As responsible young men and women, you can let people know what the truth is."

In their quest for the truth, the students had plenty of questions for the participating officers.

When do you shoot at people? (When they look like they're going to kill someone, said Sgt. Jesse Harman, head of the street crimes unit, whose officers "jump out" on drug dealers.) What do you do with the money you seize from drug dealers? (It's used for equipment, such as computers and bicycles, and other expenses that the taxpayers then don't have to spring for.)

When a youth asked Harman why police are rough with people, he explained that street crimes officers put a suspect on the ground to ensure the safety of both officer and suspect and to keep the suspect from escaping.

"It looks like we're rough, but we don't want to get in a foot chase in a neighborhood, where someone might get hurt. . . . It doesn't look nice, but how many drug dealers are nice?" he said.

Sgt. Paul Story, showing the class his police-issue Harley-Davidson motorcycle, had to fend off a number of eager youngsters who wanted a ride. "Nobody touches my baby but me," he told them. But he did let the group take turns using a radar gun to detect speeders on Eisenhower Avenue--an unusual sight that did, indeed, cause drivers to slow down--and urged the students not to be "knuckleheads" when it's their turn to get behind the wheel of a car.

An old hand at police headquarters is Burke Brownfeld, 17, who will be a senior at the Potomac School in McLean. He volunteers in the police property room and is a member of the Explorers post. But even he was in for some surprises last week.

"I'm definitely learning things I didn't know," he said, adding that the academy disproved "the theories of the police in the media and on TV. In some ways, it's nothing like what you see on TV."

Tammi Mings, 14, who will be in ninth grade at Minnie Howard, is a member of the police-sponsored drill team and would like to be a gym teacher. She said the class didn't change her perception of police, because she felt she already knew them pretty well.

"There are police around my area who are friendly. They come out and we do things with them," she said. For example, she said, a block party was held in her West End neighborhood during the National Night Out activities last week.

Scott Montiel, 14, also a ninth-grader at Minnie Howard, enjoyed the K-9 demonstration but was sold on the special operations (SWAT) team.

"I always thought police were really serious, but they can have a lot of fun," he said. He views police work as "kind of cool--you get to help citizens and stuff."

Matthew Sawh, 16, who will be a junior at Thomas Edison High School in Fairfax County, said, "It's a whole lot harder to be a police officer than I thought."

He characterized as "awesome" the trip to the firing range, where everyone donned protective ear and eye equipment and watched Officer Joe Landry, a skilled marksman, fire a handgun, a shotgun and a submachine gun. Several of the more enthusiastic students picked up the spent shells and casings as souvenirs; others, mainly the girls, kept their distance.

Some youths were also reluctant to try the firearms training simulator (FATS), which required them to aim a gun that emits a laser beam, view films of situations faced by police officers and decide whether to "shoot" the gun. The machine then tells them whether they used good judgment and whether they hit the target.

"We do this so you'll know what officers go through," Young said. "We want you to make split-second decisions like we do, to feel the pressure we're under."

Markeza Mamo, 16, who will be a junior at T.C. Williams High School and wants to be a doctor, went through the FATS exercise but "wasn't too keen on it."

"I don't like guns," she said. "I don't want my brothers playing video games that involve shooting."

The students in the class are recruited by police and by alumni of previous citizens' academies.

Also, six of the students are members of the police-sponsored Explorers post.

In general, the academy is open to any youth age 14 to 18 who is interested in learning about the police and who attends middle or high school in Alexandria. The participants received door-to-door transportation and free lunches contributed by Thrifty Car Rental and Eurest, the food service vendor at a nearby professional association.

The youth academy, with six-hour daily sessions, is similar to the police department's adult citizens' academy, held in the evenings each spring and fall, with an important exception: Because of the teenagers' inherent restlessness and shorter attention span, there is more emphasis on hands-on activities and field trips.

Indeed, at times last week, the youths were bursting with energy, and at other times, they seemed to have forgotten to eat their Wheaties.

"Wake up, you're missing the movies!" Harman said during a videotaped presentation of a drug deal, causing a drowsy student to bolt upright.

CAPTION: Left, Markeza Mamo, 16, in front at left, and Elizabeth Pettingell, 14, watch Alexandria special operations team members, above, give a rappelling demonstration at the jail next to police headquarters. It was one of many up-close and hands-on activities for participants in the Youth Citizens' Police Academy, a one-week exploration of police work.

CAPTION: Scott Montiel, 14, of Alexandria, fastens his helmet during a special operations demonstration at the police department. "I always thought police were really serious, but they can have a lot of fun," he said after participating in some academy activities.