Stranded motorists often look puzzled when they glance at Scott Zipf's smiling face, slightly hidden behind mirrored sunglasses. His expression seems out of place in a world of beer cans, fan belts and slick shoulders.

On second glance, the red safety vest, white hardhat and clipboard give him an authoritative air, as he offers a gallon of gas, a can of oil or just a cup of water to the next victim of highway madness.

Zipf is one of six guardians of the Virginia Department of Highways and Transportation's Safety Service Patrol unit who skim the state's major arteries in search of a motorist with an overheated engine, a flat tire or a dead battery.

Working in two shifts, from 4 a.m. to noon and noon to 8 p.m., Monday through Friday, the six patrollers log about 8,000 miles a week and skim the entire 200-mile network every 30 minutes, except during rush hour, said Lynda J. South, a department spokeswoman.

For the past year, the patrol has helped 9,000 motorists, from the Woodrow Wilson Memorial Bridge on the Beltway to the Cabin John Bridge, and from the 14th Street Bridge on the Shirley Memorial Highway to the Prince William County line.

What most motorists don't have, Zipf and his colleagues do. Like five gallons each of gas and diesel fuel, 30-weight oil ("I guess you might call it the cheapest brand," he said), flares, jacks, two fire extinguishers, a red flag, a first-aid kit and even squeegees. Zipf even carries a drum of cold water and Dixie cups for the distressed travelers and a 30-gallon bucket to pick up roadside debris when business is slow.

The 6-footer with sandy-brown hair keeps one eye on the road, the other on the shoulder, as he scans his territory aboard the orange "safetymobile" that takes him daily from the Wilson Bridge to Little River Turnpike, about four miles past the "split," as he calls the place where I-95/I-395 splits the Beltway.

"Every motorist should carry a spare tire with enough air and have a jack," he said. "If they're a good motorist, they'll have AAA American Automobile Association ."

But isn't that stating the obvious?

You'd be surprised, he said, at the number of people whose spares are out of air or who have the right jack but the wrong car.

Virginia is one of only three states in the country that operate a roving highway service for travelers, according to South. Illinois operates a service free to motorists near Chicago, as does New Jersey on the Turnpike.

To longtime commonwealth residents, the patrol is not totally unfamiliar. Before the days of austerity, between 1973 and 1981, the service operated 24 hours a day, seven days a week.

Still, the roving scouts are a soothing reminder that help at almost any time is on the way. According to South, 30 percent fewer cars are abandoned on the highways these days.

In 12 months, the patrol has served about 800 motorists who ran out of gas, giving them one free gallon and directions to the nearest service station. Another 900 experienced some sort of engine problem, and 1,100 had flat tires, South said.

Mark Ingwersen was a recent victim of "some sort of engine problem. I just got the engine rebuilt," he said, barely audible above the traffic on the shoulder of I-95.

Zipf offered him two gallons of water and a smile, no charge. "This is great," Ingwersen said. The expression on his face seemed to ask: Is this a mirage?

After he jotted down Ingwersen's name, address and car trouble, the highway Samaritan was on his way.

It becomes clear from leafing through the letters the department receives from appreciative customers that the road program, with an annual $86,143.20 price tag, may be one of the most popular state services, especially among those from out of state.

"We get about three or four letters a week," said a beaming Ronald J. Kari, the maintenance supervisor at the state highway department's Van Dorn station.

From James T. Faust, president of the E.L. Burns Co., to the Safety Service Patrol, came a letter postmarked Shreveport, La., regarding patroller Otha M. Vines.

Thanks for the northern hospitality and the free gas, wrote Faust. "If Mr. Vines is ever in Shreveport . . . I would love to take him out to lunch as a small token of my appreciation."

On the bulletin board of Kari's station was a letter from a couple who lauded a patroller for changing their flat tire. "It is possible," the letter said, "that they saved both our lives, and in so doing, in fact, they may have performed a much better deed than they can possibly know."

Rumbling up to Rte. 1, where he makes his turnaround to I-95 westbound, Zipf came upon a tractor trailer with a flat tire.

"Can't do much with that," he remarked, as he radioed his dispatcher, requesting her to call King Transfer in Baltimore, the company for which James Holthous drives.

Wearing a M*A*S*H T-shirt, a Harley-Davidson cap and red cords, Holthous said, "Two state troopers drove right past. I tried to flag them down, but they wouldn't stop. Hey, you have anything in there to drink? I could use a drink," he said, marveling at Zipf's easy demeanor.

Minutes later, the dispatch operator signaled that she had called Holthous' company, informing it of the breakdown.

Once again, Zipf was on the road. In two hours, he had attended four additional motorists, requesting a tow truck for a gas leak victim, offering oil to a woman stranded on I-495, giving a helping hand to a trucker to readjust the straps on his load and flagging motorists into two lanes from three at the scene of an accident on I-495 southbound.

Boarding his truck after emergency units from Annandale arrived on the scene, Zipf adjusted his hat and drove on. "I guess you couldn't make a TV series out of it. It's not like "CHiPs" or anything."

He flashed a smile and said, "It's not that glamorous."