To many Washingtonians, there's nothing more relaxing than a leisurely bicycle ride along Virginia's Mount Vernon Trail. But to Linda J. White of Alexandria, it's all in a day's work.

White, in a rotation with the four other members of the National Park Service's bike patrol, spends two days a week policing the 16-mile path between Mount Vernon and the Arlington Memorial Bridge. Though as a park ranger she is not empowered to write tickets or make arrests, White does her share to keep the trail safe and fun.

Armed with pruning shears to clear the trail, a counter to tally the number of people, and bags of tools and first aid supplies, the 27-year-old fixes broken bikes, administers emergency first aid, gives directions and teaches cycling ethics and safety. For many cyclists struggling through the path's increasing bike and foot traffic, the rangers are a welcome presence.

The trail has become so popular since it opened in 1973 that it now draws more than a half million cyclists a year, many of whom the rangers say zoom along the narrow, winding paths at dangerous speeds. In response to the heavy traffic, the bike patrol was increased to five rangers three years ago. Before that, one ranger periodically monitored the trail.

On weekdays, the path, like the roadways, is most congested during morning rush hours. Traffic picks up again around 10 a.m. when pleasure cyclists begin to cruise the trail.

On weekends, when two rangers are on patrol, the trail gets so congested that there have been frequent accidents, some serious.

On July 4, an elderly man walking on the trail suffered a cracked skull after a bike struck him from behind, she said. Dents in trees along the path show the impact of handlebars. Last September, Shirley Metzenbaum, wife of Sen. Howard M. Metzenbaum (D-Ohio), suffered severe head injuries in a fall.

In an attempt to reduce the number of injuries, rangers have begun painting yellow lines down the middle of dangerous lengths of the path. In the next few months, White said, they may install 15-mile-an-hour speed limit signs that would be enforced at some spots with radar.

Two of the most treacherous areas along the path, White said, are at National Airport, where cyclists must cross busy airport entrances, and along the southernmost part of the route between Dyke Marsh and Mount Vernon, where the trail is hilly, woody and winding.

Plans are under way to create a special tunnel that would bypass the airport entrances and to level a dangerous curve at the southern end of the path, White said. Park officials say they face a constant dilemma because straightening paths and cutting down trees may make paths safer, but many cyclists feel such measures also make the trails less enjoyable.

From a distance, White resembles any other cyclist, but on closer inspection she is clearly on official business. In her drab green uniform, with a Park Service badge and two-way radio, she turned the heads of joggers and cyclists as she zipped along the Mount Vernon Trail on her 10-speed, all-terrain Peugeot one recent morning. "I'm not breaking the law," one woman yelled.

White is constantly scooping debris off the path and reminding those around her of the rules of the road.

"Those are dangerous," she screamed at one cyclist wearing a radio headset. "Warn people that you're coming," she yelled at a cyclist who sped past a woman pushing a stroller.

White also tries to teach by example: She wears a helmet, keeps to the right side of the path and warns "On your left" when passing.

Though times are often slow, White said some days are action-packed. "Sometimes hours and hours will go by where you do nothing," she said. "But when there's an accident, you really make a difference."

White said few would envy her job on hot summer days when she has to navigate steep, unshaded inclines.

But most of the time, she says, she knows she's lucky to be away from a desk. "I like the variety," said White, who graduated from West Virginia University in 1982 with a specialty in parks and recreation.

When she and the other rangers are not on bike patrol, they work at a children's camp on Theodore Roosevelt Island and help out with activities at Fort Hunt Park.

White said she put in 1,000 miles on her bike last year and a few hundred miles so far this year. As she trudged up one hill recently, a racing bicyclist sped past her and White quipped, "I don't go fast, but I go far."