Sam Laudenslager leads a double life - attorney and legal editor by day and dance band leader by night and weekends.

Laudenslager, 30, a lawyer who does legal editing for Federal Publicans Inc., a Washington firm, heads the Kingsmen, which plays engagements throughout the Washington are and, on occasion, in points farther south.

If you ask him which job is more important to him, Laudenslager is hard pressed to give an answer.

"All I can say is, we all try to be as professional in our avocations as we are in our vacations," he said.

The Kingsmen is part of the Kings Park Civic Band, an 80-member group that is sponsored by the Kings Park Civic Association. Along with the Kingsmen, it has also spawned a German band - Die Gemutlichkeit - and a concert band.

Among them the Kingsmen is the varsity line-up, and in the two years since Laudenslager took over, its reputation has grown.

Rehearsals are held every Sunday night in a room over the Kings Park Shopping Center Hardware Store.

Laudenslager stands there, wire rims inching down his nose as he studies the music - "Everything's Alright" from "Jesus Christ Superstar."

"Ah one. Two. One - two - three - four."

He taps out the beat with his right foot.

The band catches the tune. It's awful. Ragged as a forest of tree frogs.

"Okay, okay, stop."

"We totally lost the trombones on that tempo. But that's what I want when we're out there . . ."

The band starts again. This time it's better. And Laudenslager keeps at it until it sounds like he wants it - great.

He drives himself and his musicians hard, and says it takes at least an hour to wind down after a practice session. By his own account, he's something of a Prussian, and there's at least one mini-mutiny at every rehearsal.

"But we're all good drinking buddies," he said.

And the players keep showing up for rehearsals. For most of them, playing in the dance bands is an outlet for musical interest and expertise they may not have exercised since school days.

Robert Weston, a clarinetist who is president of the Kings park Civic Band, estimates that there are about 12,000 ex-high school and college musicians living in Fairfax County. They're hairdressers, lawyers, civil servants. Twenty of them play with the Kingsmen.

Take Price Haight, in his 50s and assistant administrator for Loudoun Memorial Hospital in Lessburg. Ten years ago his sax was in mothballs. Then one night at a church social he heard the Kingsmen.

"I was enthralled," Haight said. "I wanted to get back to my horn."

He joined the band and has stuck with it for a decade. Like Herbert Oppenheim, 54, a trumpet player and another oldtimer with the group, Haight has taken on some administrative duties for the Kingsmen. He and Oppenheim manage bookings and special events such as the Springfield Music Festival, held in June at the Lake Braddock Secondary School. The Civic Band hosted the affair to celebrate its 10th birthday.

And this summer The Kingsmen played as part of the Smithsonian jazz Series on front of the Museum of History and Technology.

The Kingsmen average eight hours of practice and performing time a week during the season that stretches from April to October. The players' expenses are paid, and any profit its plowed back into the band operation - to purchase equipment and supplies.

"You can go through it fast if you know how to spend it," said Laudenslager.

Laudenslager has carried on a passionate affair with music all his life - from his boyhood in Norristown, Pa.; through his music camp days in New Hampshire when he used to play gigs with the Old Orchard Band; during his Georgetown Law School days when he played in the Redskins Band and in New Mexico, where he'd carry his trombone on business trips to Santa Fe to play in a blues club.

After he returned to the Washington are in 1974. Laudenslager rejoined the Redskins Band and took up with the Kingsmen. Now he's dropped the Redskins Band.

Now that Laudenslager has the Kingsmen whipped into shape, "and not without travail," he says, there is the question of where they're headed.

"You can't just try to keep up your present standard. You'll just slide backward," Laudenslager says.

The group sets goals for itself. This year it is to play engagements and play them well. There is an invitation for the 1978 San Juan Festival.

"Don't know if we'll make it to that one," says Laudenslager. But he is planning to take the band to the Hampton Jazz Festival next summer.

"We were invited this year," he said, "but the guys just didn't think we were quite ready for it. We decided to wait and work on it. We'll be better next year."