When Ronald Reagan looked west from the Capitol yesterday toward the simple white markers in Arlington cemetery, he recalled that a young World War I doghboy, Martin Treptow, was buried beneath one such marker.

Actually, Martin Treptow is not buried in Arlington Cemetery. His resting place is 1,100 miles away in Bloomer, Wis., a town of 3,300 about 80 miles northeast of Minneapolis-St. Paul, in the Treptow family plot at the city cemetery. His headstone is gray granite.

But Bloomer's American Legion post is named after the 24-year-old man, who left his summer job in a Cherokee, Iowa, barbershop in 1917 to volunteer for the Great War, the war to end all wars.

Eight months after arriving in France, Martin August Treptow, a private in Company m of the 42nd Division (now the well-known Rainbow Division), was killed in action on July 29, 1918, in a battle near Sergy, France, on the western front.

His job was to deliver messages between units, for this was warfare before radios and walkie-talkies. According to his obituary in the Bloomer Advance, his hometown newspaper, Treptown was nearing his destination, the lines of his battalion, when he was cut down by machine-gun fire.

In the pocket of his shirt, his fellow soldiers found a hand-written diary kept by this son of the Midwest. On the first page was the pledge -- which Reagan, another son of the Midwest, quoted yesterday near the end of his inauguaral address:

"American must win this war. Therefore I will work, I will save, I will sacrifice, I will endure, I will fight cheerfully and do my utmost, as if the issue of the whole struggle depended on me alone." Then he signed it.

Some of the men liked the sentiment and copied it. A few months later, "My Pledge," as it became known, appeared on posters urging Americans to buy government bonds to support the war, according to Jerome Reiscel, commander of the Martin A. Treptow American Legion Post in Bloomer. A congressman made it a part of the Congressional Record.

Officials at the White House press office said they were unsure how Reagan came to know of Treptow, his death and his promise to give his life for his country. According to Reiscel, the diary is here in Washington, probably at the National Archives.

The Archives, like all local and federal government buildings, was closed yesterday and could not confirm the location of the diary.

Born Jan. 19, 1894, on a small farm near Eagle Point, a township south of Bloomer, Treptow volunteered for the Iowa National Guard on June 16, 1917, according to U.S. military records. The Guard was activated for federal service a month later.

Treptown was first buried in Aisne, France, in a place called American City, with thousands of other young Americans who had so virgorously marched off to war and then died.

Later his body was brought home to the flat terrain of Bloomer. When his mother and father and two brothers died, they were bured with him in the family plot.

Treptow won no medals and no awards for his brief service. But he won a footnote in history yesterday when Reagan plucked him from osbscurity and sent reporters searching for facts about the young soldier's life.