Kathleen Humphries is trying very hard to hit the little green ball through the barn with the automatic swinging doors. Her son Scott, 9, is bouncing up and down just beyond the barn's peaked roof.

"Go ahead, Mom," he coaches. "It's kind of hard to get through the doors."

His mother swings the putter evenly, and the ball zips through before the barn doors shut. She smiles. Scott smiles.

At 9 p.m. on a balmy Friday, the Putt-Putt Golf Course on Arlington's Wilson Boulevard is in full swing. Under the bleached light of fluorescent lamps, moms and dads and toddlers and teen-agers and even a few grandparents are knocking the little colored balls through windmills and over hills and around loop-de-loops.

They've been there every Friday -- every night of the week, in fact -- for 25 years. The traffic is heavier at the intersection of Wilson Boulevard and Glebe Road than it was in 1960 around the oddly shaped 3/4-acre lot, and the Ballston Metro station has meant the beginning of new developments in the neighborhood -- including Oliver T. Carr's Ballston Plaza a few blocks away and the redevelopment of the Parkington Shopping Center just across Wilson Boulevard. But the Putt-Putt has stayed pretty much the same.

The price of a game has gone up, from 35 cents when L.J. Bruton built the course in 1960 to $2 now, and the rent on the property has surged to more than $4,000 a month. The worn green carpeting will have to be replaced soon, and even if he raises the price to $2.50, Bruton, who managed to make a profit last year, figures he'll be able to keep the course going for only a few more years before some developer wants to snatch the Putt-Putt's land, too.

"I would like to try to relocate," Bruton said, surveying the busy commercial corner from a perch on the tailgate of his blue Datsun pickup. "But there's probably no place I could afford. In an area like this, this is just a thing of the past."

The first Putt-Putt golf courses, now part of a franchise operation based in Fayetteville, N.C., were built in 1954. Now there are 1,000 all over the country and 200 more around the world, including in Japan, Australia and Canada, according to Joe Aboid, director of golf course operation for the company.

Last year, he said, 50 million people played more than 200 million rounds of Putt-Putt.

Has the game changed much in 31 years? Aboid is silent for a minute: "Well, we used to use wood rails, and now we use aluminum ones . . . . "

Bruton has been watching people play Putt-Putt for 2 1/2 decades, and he says they haven't changed much, either.

Late mornings and early afternoons, the serious minigolfers come alone to practice the finer points of putting. In May, teen-age couples in tuxedos and evening gowns sometimes play a few rounds after the prom.

The rest of the time, the course is filled with Bruton's favorite kind of customers: "Families -- that's what I like to see play," he said.

On this Friday night, the youngest member of the Allen family, 2-year-old Ben, is playing his first game of Putt-Putt. His mother, Anne, says she likes minigolf because "you can bring your little ones and people aren't offended by it. It's inexpensive and it's something you can do that doesn't take a long time."

Ben watches the last yellow ball disappear down hole No. 18 and toddles down the green toward his parents. "I want to do some more," he said.

A few holes behind, June Verzi strolls through the golf course with her granddaughter, a putter tucked under one arm and a flowered umbrella tucked under the other -- just in case.

Verzi remembers when minigolf was all the rage: "It was a big date, to go all the way to Hains Point and play miniature golf." Now there is this Putt-Putt in Arlington and a few other courses in the Washington area. Verzi brings her grandchildren every time they visit.

"What did you get on the last hole?" Christine Verzi, 17, asked her grandmother.

"Four, I think," June Verzi said, then confiding, "We're not real serious."

"Yes, we are," Christine said.

Latanya Freeman, 8, looks very serious as she bends over the green, her score card folded and clenched between her teeth.

She gives the putter a few measured swings, then swipes at the red ball, which rolls close, but not close enough, to hole No. 15.

"It's fun," Latanya said. "When we grow up and we get to be real tall, we can play real golf."

Stephanie Germana and Don Heiden, who are both 20 years old and quite a bit taller than Latanya, are still playing minigolf. "This is something different," Heiden said as the two walk arm-in-arm around the Putt-Putt course.

"We even play it at home," said Germana. "You're doing something instead of just sitting there."

The fluorescent lights slice the night sky, the cash register keeps clinking, and customers keep on lining up by hole No. 1, waiting their turns.

Bruton sits on the tailgate of his pickup and just watches. "I've been in it so long; I just enjoy it," he said. "Once you've played the game, it's sort of hard to . . . walk away and not play anymore. It's sort of catching."