Sanford (Sandy) Wiesenthal of Silver Spring has been running a solitary marathon in his mind most of his life. It's only in the past few years that he's begun to put his body to the test.

"I've always been a loner," says Wiesenthal, who at 50 just recently ran his second Boston Marathon. "And if anything is lonely, it's long-distance running. I've found my element."

He has also found a way to combine personal challenge with community service: With every mile of the Patriot's Day 26.2, Wiesenthal earns money to fight multiple sclerosis.

"People are in awe of the Boston Marathon," said Wiesenthal, who is director of general services for the Washington Gas Light Co. "Pledging money makes them feel like they have a piece of the action." By the time all the checks come in, Wiesenthal expects to raise almost $1,600 for the Athletes vs. MS fund.

Most of his pledgers are gas company employes. "I try to keep it low-key," Wiesenthal said, "but I'm still getting money now from people who didn't even hear about it in time."

Wiesenthal encountered the Athletes vs. MS campaign, which operates through many major sporting events, in 1980, when he qualified for Boston the first time. That year he raised $1,000, and the next year, although forced to withdraw at the last minute by a sciatic nerve strain, Wiesenthal received almost $200 anyway.

"This is a disease I'm seeing right before my eyes. There are two people at the gas company who have MS, one who was our poster girl for the United Way two years ago. I thought about her all the way. The fact that you're making $45 every mile, $1,000 after 20 miles, is plenty of inspiration."

As it turns out, marathons, like inventions, are only 99 percent perspiration. That other percent makes the difference when what runners call the quads--the quadricep muscles in the front of the thigh--call an unexpected halt.

"I'm at 21 miles --that's the one they call Heartbreak Hill--slowing to get a drink, when my legs tighten up completely. I can't move. My family's at the finish line, and some old friends from the Army who live in Boston, so I start hobbling, 'Okay, now you're jogging . . . now you're running . . . .' I get to the finish line and my wife says, 'You look great!' I said, 'I'm dying.' "

His final time, 3:33:20, was more than 15 minutes slower than in 1980--but not bad for a man who never ran a race until he was 45.

Wiesenthal describes himself as a lifelong spectator; a slight, Jewish "outsider" from Steubenville, Ohio, where the miners' sons stocked the football squads and the merchant's mensch played in the band.

"It was the same at Ohio State--if you're not 280 and 7 feet, don't even think about sports." He looked for other areas of competition. "That's the main reason I took civil engineering," he said. "It was the hardest thing I could find."

In the Army, where he became a cadre for a combat engineering unit, he "ended up going through basic training eight times," pushing his recruits so hard that he earned the nickname "Lt. Doubletime."

After joining the gas company in the late 1950s--in an era when utilities were still considered off-limits to minorities, and when WGL had segregated restrooms and water fountains--Wiesenthal said he was one of those who pushed the company to become involved in the inner city. After the 1968 riots, for example, WGL set up City Homes Inc., a subsidiary that bought shells of houses for renovation and sold them at cost.

About the same time, Wiesenthal allowed a doctoral candidate studying executive stress to wire him on a treadmill for a study. "The guy next to me is huffing and puffing, sweat pouring off him, and they told me, 'You got some problems.' I thought they had the wires crossed."

Gingerly, Wiesenthal began jogging. "My wife and I can still remember the first time I ran all around the block without stopping." He spent 10 years as "the neighborhood jogger, getting stares" and gradually losing 30 pounds.

In 1978, goaded into entering a 10-mile race in Annapolis, Wiesenthal was astounded to find himself at the finish line 77 minutes later, while middies fell like flies. "It was a hot August day; people were hanging on telephone poles, passing out, ambulances were screaming. I never felt so good about myself."

By St. Patrick's Day, when he completed the Virginia Beach Shamrock Marathon in 3 hours, 34 minutes, just over the Boston qualifying time, he had a permanent case of Beantown fever. "I'm still in awe of it."

Wiesenthal runs about an hour every morning before his wife, a nursery school teacher, wakes up. "That's how into running she is," he says with a smile. Meanwhile, he has become "the old guru" of jogging to several gas company employes. Washington Gas Light itself has picked up the pace, and will cosponsor the Home Town Run on May 22.

"You know the joke, there's nothing worse than sitting between an unpublished writer and a long-distance runner at a dinner party," Wiesenthal said. "Well, I don't want to bore people. I just know it works for me.