A few weeks ago, Louis Johnson, better known to the youths who live in his foster home as "Pop," caught some of his charges throwing rocks at trucks passing on Kenilworth Avenue.

Johnson gathered up all the buckets around his house and made the boys pick up every rock they could find on the Johnson's lawn for about a week. When that rock supply was depleted, he had them start digging for rocks in the ground.

The strategy was twofold, Johnson said. It would discourage the boys from throwing any more stones, and it would ease them into another project --cleared of rocks.

Lou Johnson has all sorts of strategies to keep his "sons" -- all children found by juvenile court justices to be in need of supervision or adjudicated juvenile delinquents -- occupied and out of trouble. He's also had a lot of experience.

After raising 10 children of his own, Johnson decided that he and his wife should continue on in their retirement years with the work that occupied most of their lives -- bringing up kids.

The Johnsons, who live in Berwyn Heights, are both well over 60," Johnson said. "But don't put that in," Lou Johnson said. "Everyone will think we're too old."

"Not that well over 60," interjected his soft-spoken and white-haired wife, Catharine.

"We had seen everything we wanted to see, Momma and me . . . I guess I just felt guilty sitting around doing nothing, "explained Johnson, a bear of a man with a thundering voice.

So, when the Johnsons saw an advertisement for house parents for Family Homes, Inc., the organization that runs seven foster homes in Prince George's County, about a year ago, they decided to apply.

Stanley Levy, Family Homes director, said they were just the sort of stern but empathetic people he is always looking for to act as house parents.

Mrs. Johnson was apprehensive at first. "I had been away from it for quite a few years, you know," she said quietly. After Johnson retired from the manufacturing business in 1971, however, the couple decided that the Florida retirement scene was not for them.

"Everybody there in Florida was just sitting around waiting for something to happen, but working with these boys, you know something is always going to happen," Johnson said.

When he's not checking out the area around Greenbelt Junior High School where some of his boys attend school -- to make sure they're not truant -- Johnson works with the boys on family projects, constructing a fence, planting a garden, building walkways around the house with the rocks the youths dug up.

Is it harder raising these children, many with problems, than it was when the Johnson's own 10 children --were young?

"There's not a damn bit of difference," Johnson said. "Oh sure there's a few more dopeheads now, but the basic values are the same as they were in the 1950's. You teach a kid to be good and kind and not hurting."

The youths at Johnsons' house said they like the way "Pop" expects them to keep up with their school work and hold onto the after-school jobs he helps find them.

"He's strict but fair. You can have a lot of fun with him," said one youth from Baltimore, who has lived with the Johnson's for almost a year.

"If nobody disciplines you, then you think you can get away with anything," another youth chimed in.

"No kid wants a parent who's a pal. They have their own friends. They want a Daddy," Johnson said.

Johnson recalled that when two foster parents new to Family Homes visited his house recently to ask advice on being house parents, one of the boys advised them, "Better get a rock pile."