The hottest thing in Boy Scouting and Girl Scouting used to be the merit badge. Now it's the police badge.

Across the country, 133,000 teen-agers have joined the National Law Enforcement Explorers Conference, making it the most popular area of senior scouting in the country. Within the past five years, 20 posts have been formed in the Washington-Baltimore area alone, including those in Montgomery, Howard, Prince William and Prince George's counties, the District, Alexandria, McLean, Vienna, Herndon, Reston, Fairfax City and Leesburg.

Instead of learning to start a fire with two sticks, these scouts learn such urban survival skills as directing traffic and recognizing that screwdrivers and letter openers are potential weapons.

At their national conferences, Explorers compete for awards in arrest and search techniques, court testimony, crime scene search and hostage negotiation. They also distribute police promotional literature and sponsor police displays at local shopping malls.

"When I was young, I watched 'Superman' and 'The Lone Ranger.' They were my heroes," says Officer Joseph Tauro, director of the eight-year-old West Springfield post, the oldest in the area. "Kids today don't have heroes. All they hear about is who's held hostage, or who's killed who. The police are the last of the good guys."

Not since the Dead End Kids aspired to be Junior G-Men have so many teens practiced to be policemen. And some Explorers follow through, entering public, private or military law enforcement, including about a dozen from the West Springfield post in the last two years.

"I hadn't even considered law enforcement before I got into the post," says 22-year-old Anita Colvard, now a Fairfax City police dispatcher. "But aside from school, it became my main interest."

Colvard, who joined the West Springfield post in 1977 at 17, eventually served as captain of newly formed McLean and then Fairfax City posts. She now is an adviser to the Fairfax City Explorers.

The majority of Law Enforcement Explorer posts are sponsored by local police departments, which pay the $35 national charter fee and help develop the national training program. Explorers study virtually all aspects of law enforcement work: firing on the pistol range, handling K-9 patrols, examining crime scenes, and writing reports.

They spend a week each summer at a junior version of the police academy. After a six-month probation, scouts who pass a test on radio codes may ride a couple of times a month with officers on patrol. Unlike the fictional police in television dramas, who are depicted working in pairs, Fairfax police generally patrol alone, so Explorers sometimes have an opportunity to assist an officer.

Tauro tells of one Explorer who kept a distraught woman talking and calm while the officer arranged her institutionalization. Another scout untangled a traffic jam, leaving the officer free to investigate the accident that had caused it.

While serving as security officers at Clifton Day festivities, Explorers spotted three men breaking into an abandoned house, reported the crime and detained the suspects until police arrived. In a rare instance a few weeks ago, two of Tauro's underaged Explorers were used to buy beer as part of an investigation of illegal sales of alcohol.

"It's not exciting every night," says Scott Durham, 19, of Woodbridge, a Fairfax City Explorer and student at Virginia Commonwealth University in Richmond. "But you do help people, whether in accidents or domestic cases, or just giving directions."

Explorers spend most of their time helping police. They prepare information displays at shopping malls, control traffic and parking at scouting and police events, and assist with the Special Olympics held for handicapped persons.

"This is really the only youth-outreach program the police department has hands-on control over," says Tauro. "I mean, you can coach a football team, but that's 10, 12, maybe 15 kids. We have more than 100 kids in three Fairfax posts, 55 here in West Springfield, and it's increasing every meeting."

"The police department that does not have this program is losing out," he adds. "People tend to generalize, and police officers are the stubbornest people in the world. If they only deal with the 5 percent of kids who are troublemakers, they tend to blow it out of proportion. These are the best kids in the world."

Durham says the program gives youths an understanding of police. "I think Explorers gives people an inside opportunity to see policemen as people, not just as authority or establishment figures," he says.

The popularity of police-sponsored scouting points up a change in the often negative image of police officers prevalent 15 years ago.

"When I was at George Mason," said Colvard, "a lot of the teachers and graduates had been in their teens and 20s during the 1960s, and their attitude was very antipolice. They said a lot of things I just couldn't agree with."The ideals of religious faith, personal honor and national pride are written into the applications for membership in Law Enforcement Explorer posts.

"I was pretty liberal before," says Colvard. "It taught me to be more conservative about most things."

More importantly, says Tauro, the program teaches confidence, efficiency and good citizenship.

"These kids at the West Springfield Post performed 10,000 hours of service last year," he says. "Not $10,000--10,000 hours. And that's worth a lot more."