It is afternoon rush hour in Arlington and a car goes up South Dinwiddie Street in the southwest Arlington neighborhood of Claremont heading toward the Fairfax County line.

Abruptly it stops. There is a new traffic diverter at the Chesterfield Road. Instead of going straight, as most drivers used to do, signs posted on a traffic island tell the driver to turn right into an extensive detour.

That's fine with some residents of Claremont, particularly those who live on South Dinwiddie Street. Their street runs parallel to crowded Rte. 7 and many commuters had been using it as a shortcut.

But while the diverter has cut the number of cars on Dinwiddie, it has caused a huge jump in traffic on neighboring streets and touched off a civil war. Emotions are running so high on whether to keep the diverter that some residents, citing fears for their safety or that of their children, declined to be interviewed.

The controversy has also raised the larger question of the balance between one neighborhood's needs and the good of the community at large. In a county that prides itself on its numerous and active neighborhood civic associations, the diverter debate has turned into a particularly touchy issue.

"People don't think of themselves as Arlingtonians, let alone Virginians," said Richard A. Staley, a member of the county Transportation Commission who is one of a minority that usually opposes diverters. They identify with their neighborhood, he said. "It's a very narrow viewpoint."

Some complain that diverters make driving in Arlington even more confusing. "Where in Arlington is there a straight street that doesn't dead-end somewhere?" asked one longtime resident.

One thing almost everyone agrees on is that development is responsible for much of the problem, particularly the huge office, condominium and shopping projects that have sprung up along Rte. 7 in Alexandria.

The added traffic from the new buildings, plus a series of poorly timed traffic lights, have sent commuters onto alternate routes such as Dinwiddie.

"We are taxpayers," said Tom Anzalone, who heads a group of nearby condominium owners opposed to the diverter. "We pay a lot of tax money for the upkeep of the streets and we feel we should get to use the streets." Anzalone was one of dozens of people who wrote or telephoned members of the County Board protesting the diverter.

"Maybe it wasn't planned that way, but because of the way things developed {Dinwiddie} has turned into a major street. You have to accept that things change," Anzalone said.

Retorted Robert L. Beskind, president of the Claremont Civic Association: "Everybody says you have to change with the times, unless it affects them."

Nancy Jennings, who lives on Dinwiddie, said that before the diverter was installed, vehicles ranging from delivery trucks to empty Metro buses used the street as a shortcut. The slowdown of traffic has meant "a return . . . somewhat to sanity," she said.

Her street was designed by planners to connect the Claremont neighborhood with major thoroughfares, she said. It was "not put in there for people who live in Fairlington {condominiums} to get to Hechinger's" hardware store, she said.

"Do people who don't live in a neighborhood have the right to use neighborhood streets for their convenience?" she asked rhetorically. "Or is it more important for residents to preserve property values and the safety of their lives?"

Even Jennings said the diverter was not an ideal solution. "The problem is, what would be better," she said. "If you allow the amount of traffic to increase unbounded, you destroy a community."

John Quinn, a county transportation Commission member, agrees. "People do not have an inalienable right to travel on a route that was not intended to carry significant traffic," he said.

A study done last year by Arlington traffic engineers found that up to half the rush hour traffic along Dinwiddie Street was not neighborhood traffic.

The street was carrying from 4,000 to 5,000 cars a day, more traffic than it should, said Jeffrey A. Sikes, a planner with the Arlington Department of Public Works, although the accident rate on the street is not unusually high.

Residents had long sought to stop some of the cut-through traffic in the neighborhood, and the diverter was suggested by the county as an experiment. After a majority of the residents in the neighborhood signed a petition supporting the test diverter, it was approved by the County Board and installed in August for a 90-day trial.

Just about everybody is now unhappy with it. "We've had a 380 percent increase in traffic in front of our house," said Roy Markon, who lives on Culpeper Street one block from Dinwiddie. There used to be about 350 cars a day on Markon's street. Now there are more than 1,200 a day.

"All you're doing is taking somebody's problem and moving it to somebody else's street," said Markon, who drafted a petition signed by about 40 of his neighbors asking that the diverter be taken out before the trial period is over.

Other residents are unhappy because they say the police have failed to enforce the diverter's restrictions. Some drivers have ignored the signs and illegally proceeded down Dinwiddie.

The County Board held a second hearing on the issue last month and told residents to try to work out a compromise. The board will not consider the matter again until late next month, conveniently timed, some say, until after the county elections.