At the National Archives, Ms. Blanton had been working with 19th-century Army records for several years when she stumbled on a file kept by a postwar clerk in the Adjutant General's office; it was about women caught serving in the armies of the Civil War. ''There were handwritten notes, obituaries that were clipped out; it was a carefully kept file,'' Ms. Blanton says. ''I had never heard of such a thing as women Civil War soldiers, and I was fascinated.''

Ms. Cook, 45, had seven Indiana ancestors who fought for the Union, including one, Col. Absalom Hanks Markland, who served on the staff of Gen. Ulysses S. Grant. After the war, Grant gave Markland the saddle he had used during the Civil War as a token of his esteem. Ms. Cook's middle name is Markland, after the colonel. Still, she says, she was more interested in the American Revolution than in her family's role in the Civil War.

That changed after she married. Her former husband, Frederick Burgess, is an avid Civil War buff. At their 1990 wedding, they dressed in Civil War-era clothing and cut their wedding cake with a 130-year-old officer's sword. On weekends, Ms. Cook started accompanying him to re-enactments of famous Civil War battles. Most of the other women she met there were dressed in hoop skirts and portrayed more traditional female Civil War roles, like grieving widows or sutlers, merchants who traveled with the armies and sold goods to the soldiers. Ms. Cook, a flutist, wanted to play the fife and drums during battles, something that required taking to the field dressed as a male soldier. Eventually she also learned how to shoot a musket.

One day Ms. Cook received a letter from Ruth Goodier of Chipley, Fla. Ms. Goodier said she had heard of Ms. Cook's lawsuit and supported her right to serve as a male soldier during re-enactments. She added that she knew women had fought in the war because her great-grandmother's older sister, Sarah Rosetta Wakeman, had served two years, and that she had a collection of Wakeman's letters home from the front. She also had a daguerreotype of Wakeman, dressed in her uniform, holding her musket with the bayonet attached, that had remained hidden in a family attic for years.

Ms. Cook was astounded, since no collection of letters written by female soldiers was known to exist. In the hope of getting the letters published, she started researching the life of Wakeman, who used the name Lyons Wakeman while serving in the 153rd New York Volunteer Infantry. Wakeman saw action around Washington and in the 1864 Louisiana Red River campaign before dying that year in an Army hospital from the effects of chronic diarrhea. Oxford University Press published the Wakeman letters, edited and annotated by Ms. Cook, in a 1994 book entitled ''An Uncommon Soldier.''

It was while researching the Wakeman letters at the National Archives that Ms. Cook and Ms. Blanton met and talked about pooling their resources and writing a book together about female soldiers. In the beginning, they simply set out to document as many as they could find. This alone was a challenge, as many of the women came from working-class backgrounds and couldn't write. Others went home after the war, married and had children, and, not wanting to seem different, never talked about their war experiences. But Ms. Blanton and Ms. Cook quickly realized that they didn't want just to tell the stories of the individual women who had served. They also wanted to set them in a context, to explore how the women fit into the broader society.

''One of the things that bothered me when I was asked to leave the Antietam battlefield after portraying a male soldier was the attitude of the park officials there,'' Ms. Cook recalled. ''They considered Civil War women soldiers eccentrics and oddballs, that something wasn't quite right about them.''