Louisa May Alcott inspired generations of girls with her own portrait in “Little Women” as rowdy, moody Jo March, who wished she had been born a boy, loved to run and skate, wrote plays with dashing parts for herself and “scribbled” stories to support herself and her family.

A much fuller portrait of this fascinating woman emerges in this absorbing new biography by screenwriter Harriet Reisen, who worked with Emmy Award-winning producer Nancy Porter to create a marvelous documentary — a project some 20 years in the making — about Alcott for the “American Masters” series on PBS scheduled to air in late December.

Reisen’s cinematic sensibility makes for a marvelous book, impossible to put down, with its finely drawn portraits of characters who come alive in a couple of sentences, a book rich in affecting scenes and colorful anecdotes and a fine sense of both the intimate personal detail and the historic backdrop of Alcott and her family and their place amid the great minds of 19th century New England.

Reisen draws on journals, letters, recollections of friends and contemporaries and Alcott’s books (including her contemplation of suicide, referred to in her novel “Work”) for this lively narrative. She even did some detective work that turned up a previous biographer’s 1975 interview with 96- year-old Lulu Nieriker Rasim, Louisa’s niece and the only person then still alive to have known Alcott. Lulu’s memories of her famous aunt (who died when Lulu was 8 years old) are published here for the first time.

Among the highlights of this fascinating life:

Alcott dismissed her writing for children as “moral pap for the young,” preferring her secret literary production of thrillers featuring murderers, transvestites and revolutionaries.

As a girl, Louisa was tutored in literature by Ralph Waldo Emerson, in natural science by Henry David Thoreau. Both were her neighbors in Concord, Mass.

Her books sold better than those of such luminaries as Emerson, Hawthorne and Melville.

Alcott was an early proponent of running and exercise; she ran every day.

She may have suffered from manic depression. (Her mother made note of Louisa’s black moods when she was only 10.)

A radical abolitionist like the rest of her family, Alcott wrote an inter-racial romance and included a “quadroon” among the pupils of Jo’s school in “Little Women.”

Reisen draws a nuanced portrait of Louisa’s complicated relationship with her father Bronson Alcott, a self-educated philosopher whose refusal to work for wages impoverished his family — and whose disastrous utopian experiment at Fruitlands nearly ended his marriage. (Louisa as an adult would write: “A philosopher is a man up in a balloon, with his family and friends holding the ropes, trying to haul him down.”)

Reisen perceptively notes how different Louisa’s life was from that of her wealthy cousins and other middle-class girls. Her family lived on handouts and hand-me-downs, hounded by creditors, and feasted on meals of bread, apples and water. (Louisa had moved 30 times before she was 25 years old.) “At almost nine, hunger told her how dire things were ... Her raw hands reminded her that she and Anna performed dirty chores their playmates never thought about; in ‘Little Women,’ she would give the March family a servant, and she herself would have ten when she died.”

Among the memorable scenes in this beautifully written narrative: Louisa (who contracted typhoid during six weeks as a Civil War nurse) comforting a mortally wounded young blacksmith, holding his hand when he died; Louisa running with sister May to save Ralph Waldo Emerson’s books from his burning house; Louisa nursing her dying 23-year-old sister Lizzie, “who looked like a woman of 40, all her pretty hair gone”—a scene she would romanticize for “Little Women,” which Reisen considers “among the most affecting scenes in all fiction.”

We are also reminded that Alcott’s was a stirring rags-to-riches tale. Louisa was not even into her teens when her mother, Abigail, expressed the wish that Louisa would someday help support the family. At 15, Louisa vowed: “I will do something by and by. I’ll be rich and famous and happy before I die, see if I won’t.”

Mrs. Alcott’s job as “missionary to the poor”— and the family’s move to a basement apartment on the fringe of Boston’s South End — gave Louisa a close look at urban-style poverty. “The teenager stranded in the basement dump,” Reisen notes, wrote a novel, “The Inheritance,” of a young woman living in half-mansion, half-castle.

Reisen includes a detailed accounting of Louisa’s publishing output and earnings, including the $32 she made at age 21 selling her first book, “Flower Fables,” and notes her rare skill at tailoring her work for the market, producing and selling poems, stories, popular fiction and literary fiction to support herself and her family.

Fans of “Little Women” will be intrigued by Reisen’s detailed account of Louisa’s relationship with Ladislas Wisniewski, a Polish nationalist 10 years her junior who was the model for Jo’s friend and would-be-lover Laurie.

Although Alcott and her doctors believed the mercury-laden calomel she was dosed with for typhoid caused the health problems that began to plague her in her late 30s, Reisen includes speculation by modern medical professionals that Alcott may have suffered from lupus, citing the telltale butterfly rash on her face in an 1870 portrait.

A master at creating jolly tales from a life of many troubles, Alcott emerges here as the life of the party, running off to the docks at age 4 to show the sailors her new green shoes, walking 30 miles to visit a friend, hamming it up as a character actress on stage, or shaking her feather duster in the faces of fans who knocked at her door.

One quibble is that Reisen waits for dramatic effect until the end of the book to mention the religious awakening Louisa experienced at 13 — a realization of God’s presence in the natural world. This surely should have been mentioned earlier.

Scholars quoted in the PBS documentary agree that “Little Women” is a great book but disagree as to whether Alcott belongs in the ranks of the greatest American writers. Reisen notes that “Little Women” has never been out of print in 140 years and that it helped inspire the careers of women as diverse as Gertrude Stein, Simone de Beauvoir, J. K. Rowling and Sandra Day O’Connor.

As this biography makes clear, Alcott was an American hero. She was a pioneer in publishing, a feminist, an abolitionist, a Civil War veteran, a philanthropist. She inspired generations of girls to aspire to more than marriage and children by her example. More than that, as Reisen says: “She was her own best character.”

Jean Westmoore is The News’ children’s book reviewer.