At Langston Golf Course, customers do not have to worry any more that their golf balls will be stolen by neighborhood youths hiding in the woods along the 13th fairway.

"I hired 'em," said Wallace (Sarge) McCombs, the manager. "Put 'em to work shagging balls, and all of it stopped."

Golfers have noticed other improvements, too, in the five years since a new private contractor took over the ailing 18-hole course on the Anacostia River in Northeast Washington. The grass beside the fairways no longer resembles a wheat field in Kansas. The greens live up to their name. Along the back nine, there hasn't been a mugging in years.

But now comes another threat to Langston Golf Course, one that has nothing to do with crime, weeds or urban decay. Mayor Marion Barry wants a new football stadium, and Langston, according to suggestions voiced in recent days, is one place he might consider building it.

That makes regular patrons of the course, many of whom remember Langston from the days when it was one of the few places blacks could play golf, more than simply mad.

"It makes me nauseous," said Joe Cole, 74, a former director of the D.C. Department of Recreation and a patron for 40 years.

That level of concern may be premature. The mayor's office is months from a decision on whether to build a new stadium, let alone finding a place to put it. The National Park Service, which owns the course, says it has every intention of leaving Langston as it is. Negotiations for a new 15-year lease are under way now.

"The golfers over there love it, as far as I know," said Don Rousch, who oversees park service concessions in the region.

Nevertheless, the mere suggestion that Langston's greens and fairways could someday be plowed under is enough to make some people start to worry.

"What bothers me is this is a political town, and it depends on what button is pushed," said Robert Brock of Golf Course Specialists Inc., which operates the three public courses in the District. "If someone on the Hill pushes a button, then the park service would have to fold on the deal."

That would be a cruel irony for Langston, which has undergone a renaissance of sorts after years of neglect. "The greens were terrible, the fairways were terrible and it just wasn't a fun place to play," said Rousch. "Frankly, we were about ready to close it."

McCombs, a retired sergeant with the division of federal protective services, vowed to change all that when he took over as manager two years ago. First he cleared the trash off the greens and fairways. "Tires, beer bottles, you name it," he said. Slowly he got the course back into shape.

He also tackled the crime problem, staking out the course late at night to catch the vandals who made off with the flags that marked the holes or took the golf carts on midnight joyrides. He installed water coolers and portable toilets at the tees and put up a sign against cursing in the clubhouse. There is talk of an irrigation system.

Slowly but steadily, people have started to come back to Langston. Annual patronage at the course has climbed steadily, from 20,000 a few years ago to 33,000 last year to a projected 40,000 this year, according to Brock. Gross yearly receipts are expected to top $150,000, up from $70,000 in 1983.

"One thing you'll notice is an increase in white Caucasians, Orientals and all," said McCombs. "And there weren't any a few years ago."

Now, without a whisper of warning, comes word that Langston might make a good place for a new stadium. The site was presumably mentioned because of its proximity to Robert F. Kennedy Stadium, which Redskins owner Jack Kent Cooke has said is too small. But few people are rushing to claim credit for the idea today.

Last week, a spokesman for Barry said the mayor had discussed the idea with Cooke in a meeting on Monday. In an interview Friday, however, the mayor dismissed the question of sites as "a red herring."

Whatever the origin of the proposal, the golfers at Langston are not about to lean idly on their clubs while the city ponders its next move.

"The mayor should have my telegram on his desk by now," said Andrew Humphrey, a retired school principal. Joe Cole, who said he has played at Langston with the likes of Joe Louis and Jackie Robinson, has fired off a letter to D.C. Council member John Ray. Petitions have already begun to circulate.

And Eddie Brent has come up with a site suggestion of his own. "Tell them to build it in Chevy Chase."