Theodore Bacon was driving along Virginia Rte. 681 in Loudoun County near dawn recently when a deer bounded out of the darkness and into the path of his 1980 Honda.

"I never even had a chance to hit the brakes," said Bacon, a rescue squad worker from Lovettsville. "I swerved to avoid the deer but ended up hitting it anyway." Bacon's next moments remain a blur -- a fence etched in the night by the headlights of his car and the momentary sensation of being airborne as his car went over an embankment.

His car rolled over three times. Bacon was wearing a seat belt and was not thrown from the car. He was extricated 10 minutes later with only a scratch on his right hand. The car, valued at $4,800, was demolished.

The deer-related accident is one of an increasing number of such incidents occurring in Northern Virginia counties. Herds of deer ranging for food and mates are increasingly crossing paths with man as new roads and subdivisions are being carved into the white-tailed deer's natural habitat west of Washington.

In Virginia alone, the number of reported crashes between vehicles and deer has climbed by 25 percent in five years. Some Virginia motorists have resorted to attaching high-pitched, wind-activated whistles to their vehicles in an effort to scare the animals.

But game wardens say the thick patches of grass found along roadsides in the spring and the salt laid on highways during the winter's storms are irresistible lures.

"It is when they come close to the road that we have our problems," said Rick Loving, a Virginia game warden in Warrenton, 45 miles west of Washington. "This happens mainly during two times of the year: the fall and the spring. In the fall, the bucks are in rut and looking for mates. In the spring, the does are skittish and anything scares them when they are ready to drop fawn."

Highway officials have marked many roads with deer warning signs, but police say a pair of distant, luminous eyes staring in the dark frequently is the only warning a motorist gets. Usually there is only the fleeting image of a deer making a spectacular leap into the blinding beams of the headlights before a resounding crash.

Because the eyes of deer are more light-sensitive than those of humans, the nighttime encounters with cars often are fatal. "Deer become mesmerized by the bright lights," said Jack Raybourne, game division chief of the Virginia Commission of Game and Inland Fisheries. "They don't know what the lights are. They will try to jump across them. Maybe the first one makes it and then, bam! The second or third deer gets it."

When a car moving 55 miles an hour hits a deer that weighs between 135 and 150 pounds, the collision might not only kill the deer and damage the car but also seriously injure the passengers.

There were 109 persons injured and 3,127 deer killed by vehicles on Virginia highways in 1983, the latest annual statistics available, according to Raybourne. He estimated that only half the deer deaths are reported to authorities.

The magnitude of deer kills on Maryland roads has not reached the proportion of the Virginia problem but still is bothersome, police there say. In 1983, 943 deer were killed on Maryland roads, up from 835 in 1979.

"It's a very serious problem not only because of the impact on deer but because of the damage it causes to human life and property," said Dick McCabe, publications director for the Wildlife Management Institute.

Robert Gianniny, a claims consultant for State Farm Insurance at the firm's Bloomington, Ill., headquarters, says that the cost of a claim for car and truck damages from deer accidents typically ranges between $700 and $1,000.

"I was surprised to see the number of deer cases, particularly in the rural areas to the west of the D.C. metro area," Gianniny said. "We are getting more and more claims all the time."

Drivers who see the deer stumble and then continue running generally believe that the deer survives. But game wardens say the injured animals often run back into the woods, collapse and die.

The number of Odocoileus virginianus, also known as the Virginia white-tailed deer, has been steadily growing since the early 1900s when unlimited hunting, clearing land for timber and farming nearly drove the species to extinction.

Decimation of most of their natural predators -- primarily wolves -- and protective hunting laws have led to a rise in the number of deer to 500,000, or between 20 and 25 per square mile, Raybourne said.

White-tailed deer are "good breeders" and considered one of the most successful wildlife species. Hunters annually thin the herds by about 90,000, a number supposedly matched by illegal kills. Still, the deer population continues to grow.

Deer have learned to cope with most of the obstacles suburban man has imposed. Highways landscaped with grasses and shrubs to prevent erosion serve as feeding grounds for them, the game wardens say. The deer live comfortably in close proximity to towns and often treat homeowners' prize gardens and shrubs as salad bars.

The animals most often are killed along Northern Virginia roads in the counties of Fairfax, Fauquier, Culpeper, Stafford, Rappahannock and Loudoun. The last has the state's highest number of roadside deer kills. There is a tract of about 7,000 acres in Loudoun where corporations such as Xerox, International Business Machine Corp., Magnavox and others forbid hunting, which has provided a refuge for deer. Virginia Rte. 15, which runs through the area toward Leesburg, is a killer stretch for deer.

"I am always looking out for eyes," said Jean O'Meara, an executive secretary at the Xerox training center near Leesburg. "Since February, I have had to stop five times for them . . . . They can really mess up a car. Unfortunately, they lose their lives."