The Thomas Eakins Collection of the Hirshhorn Museum, one of the largest extant, goes on view today for the first time at the Hirshhorn. It is not the usual accumulation of borrowed masterpieces, but rather an in-house study of the development of one of American's greatest painters.

Usually it's the curators who have all the fun, investigating the evidence of an artist's lifetime, making the discoveries, and then selecting out only the finest examples for exhibition. As a result, what the viewer usually sees is a pristine package that says much about the art, but little about the artist, who often remains on enticing but elusive figure.

Not so the Hirshhorn's new show of paintings, drawings, photographs, sculpture and memorabilia from the life of this penetrating realist from Philadelphia, the oldest old master in the Hirshhorn collection. (He was born in 1844 and died in 1916.) Acquired chiefly from the accumulated holdings of two Eakins students and colleagues, the Hirshhorn's collection begins with drawings by Eakins the schoolboy, and ends with his last, unfinished portrait of a Dr. Spitzka. In between, discoveries and insights abound for even the most casual viewer.

It is interesting of course, simply to read the Eakins' father was a writing master and calligrapher, and exerted a powerful influence over the young artist. But how much more fascinating it is to see the evidence first-hand - as in the extraordinary map of Switzerland with its splendid calligraphy, made while Eakins was a boy of 12 at the Zane Street Grammar School in Philadelphia.

And though we know that champion rower Max Schmitt was the subject of one of Eakins' most famous paintings - and one of the greatest American genre scenes of the 19th century - how much more meaningful future readings of that painting become after reading Schmitt's letter to his old school chum, Tom Eakins, asking when they will again be able to share a swim in their beloved Schuylkill river.

The show moves on, chronologically, through the victories and numerous defeats of Eakins' life. After high school, where his genius for draftsmanship was much in evidence, the artist was sent to Paris to study at the Ecole des Beaux-Arts under Jean Leon Gerome. Obviously something of a homebody, Eakins here writes his mother, complaining "I haven't yet got my first letter from home," and includes several sketches of his Paris studio, washstand, fireplace, bookladen table and all.

After a brief stopover in Spain, where he was deeply affected by the realism of Velasquez, Eakins returned to Philadelphia to stay. There he became first an instructor, and ultimately head of the prestigious Pennsylvania Academy of Fine Arts.

Included in the Hirshhorn collection are several studies for major paintings from this period, "Arcadia" and "The Swimming Hole" among them, along with several photographs which Eakins was among the first to use as a tool in evolving his carefully worked, classical compositions. There is also evidence of Eakins' collaboration with photographer Eadweard Muybridge, with whom he pioneered photography showing human and animal locomotion.

Eakins' admission card to classes at Jefferson Medical College here attests to his interest in human anatomy, culminating in his great "Gross Clinic." This work, however, was relegated to a medical hall at the Philadelphia Centennial Exhibition because it was considered too shocking to be shown as art.

This was not the first time Eakins' abiding concern for the workings of the human form was to cause him grief. In 1886 he was fired from the Pennsylvania Academy for removing the Ioin cloth from a male model in a drawing class for women. He continued to teach at the Art Students' League of Philadelphia, founded by some devoted students, but eventually abandoned nude compositions for portraiture, which preoccupied him for his remaining years.

Along with several profound and probing portraits seen before at the Hirshhorn, including that of Mrs. Eakins, there are several portraits - some good and some bad - which were refused by their subjects, including one of Mrs. Joseph Drexel. They give some indication of the difficulties Eakins encountered in gaining acceptance in the face of more fashionable work by contemporaries like Sargent and Whistler. After decades of being ignored, he was finally admitted to the National Academy of Design as an old master. After his death in 1916, his reputation flagged once again until the resurgence of interest in 19th century American art in the 1960's.

"The distance between Victorian disapprobation and contemporary reappraisal has not been sufficiently retraced to dissolve the myths that surround Eakins, the man and the artist," says Hirshhorn director Abram Lerner in the exhibition's catalog. As a result, an all-day symposium on Eakins is being held at the museum today.