Somebody's idea of a practical joke, Dennis Corbett said to himself when the signs went up, overnight and without warning, on Nutley Street last week.

"Private road," declared bright red, authoritative-looking signs. "No trucks or buses."

"It tickled me," said Corbett, a Fairfax County merchant who has run a clothing store at Nutley Street's Pan Am Shopping Center for two years. "How the hell could this be a private road? I thought it was a hoax."

The signs were no hoax. Nutley Street, a major artery through the center of Fairfax County leading to the Vienna Metro Station and carrying several thousand cars a day, is indeed a private road at its southernmost stretch, between U.S. Rtes. 50 and 29. Unlike most Northern Virginia roads, the street has never been owned or maintained by a state or local government.

The driver of any vehicle, not just buses or trucks, who wants to use the private section of Nutley Street does so only with the good graces of developers Cyrus Katzen and Efrain Guerrero, who own the road as part of a general partnership based in Baileys Crossroads, according to county officials and land records.

"The road is not a public right of way," said Robert Moore, an official in the Fairfax County Office of Transportation. "As I understand it, they could build a fence across it if they wanted to."

Katzen did not return repeated telephone calls to his office, and Guerrero, saying he was in litigation against his partner, declined comment.

However, Pan Am merchants and county officials said the new signs, like several no-parking signs erected along Nutley Street earlier this year, appeared to be Katzen and Guerrero flexing the muscles of ownership. With the opening of Metro, increased traffic has led to concerns over the condition and safety of the road, merchants said.

Although the fact that Nutley Street is in private hands surprised many merchants and motorists, Fairfax County officials said the sign was only a reminder of the bad taste left in their mouths when the road was built seven years ago. The builders of the Pan Am Center, a firm associated with Katzen that later sold the plaza, refused to build the Nutley Street extension to the quality standards necessary to incorporate the road into the state highway system, according to county officials.

Another major road that remains partly in private hands is a section of International Drive at Tysons Corner, Moore said.

Although there have been requests from citizens and elected officials for the county to take ownership of the private part of Nutley Street, with the eventual goal of turning it over to the state, that prospect is unlikely.

Virginia would not accept the southern end of Nutley Street unless major improvements were made to the road's surface, and Fairfax has no money budgeted to improve the road, said Claude G. Cooper, director of the county's Department of Environmental Management.

The contrast between the public and private sections of Nutley Street will become even sharper within the next year, as a major, multimillion-dollar expansion of the road from four lanes to six north of Rte. 29 to Vienna is scheduled to begin. No improvement is scheduled for south of Rte. 29.

"It just doesn't seem logical," said Corbett. "How can a major road be privately owned?"

Corbett, like some other Pan Am merchants, has had another concern since learning that part of Nutley Street has a status little different from a private driveway.

"If they can stop buses and trucks, what's next?" he said. "Who else can they stop?"