CUSTER, by Robert D. Ingham. Directed by Louis W. Scheeder; musical direction and vocal arrangements by William Penn; set and lighting by Hugh Lester; costumes by Rosemary Ingham; choreography by Virginia Freeman. With Tom Blair, Sandy Faison, John McMartin, William Newman, Maggie Thatcher, Ricki G. Ravitts, David Cromwell, Robert Murch, John Mansfield and Allan Carlsen. At the Terrace Theater through Nov. 18.

George Armstrong Custer had 13 horses shot from under him during the Civil War, according to "Custer," which opened at the Terrace Theater Saturday night.

It would be interesting to hear one of those horses assess Custer's qualities as a leader. That's about the only testimony missing from Robert E. Ingham's low-keyed but gracefully written and intriguing play -- a kind of oral history of the Battle of Little Big Horn, in which the parties occasionally interrupt each other to contradict or clarify a point of dispute, but otherwise stand back politely and let each, in his proper turn, present his account.

Besides Custer, the witnesses include his widow, Libby, and the two men on whom she and the pro-Custer faction laid the greatest blame for the 1876 massacre: Maj. Marcus A. Reno, who was so awed by the prospect of charging into an encampment of thousands of Sioux that he charged the other way instead, and Capt. Frederick William Benteen, who battled the Indians valiantly on the bluffs but, according to his detractors, passed up the chance to ride to Custer's rescue.

With a hot toddy in his hand and a hazy burden of guilt on his conscience, Benteen is a fascinating, highly stageworthy fellow -- as researched and written by Ingham and as played by John McMartin, a fine actor who seems to have developed a special sympathy for the part.

Benteen despised Custer for his petty vengefulness and his customary strategy of "no reconnaissance, divided command, just pitch in and pray to God." Wryly deleting an "f" from the title of Custer's memoirs, Benteen refers to them as "My Lie on the Plains." But he must also admit that, had he not nourished such a hearty contempt, he might have worried more about Custer's fate at Little Big Horn and perhaps even have done something to save him.

Ingham, a former actor at the Milwaukee Repertory Theatre, among other Midwestern sites, became acquainted with Custer in the library of the University of Montana, while teaching drama there. But, says the playwright in a delightful program note, "I quickly saw that it was not possible to write a play -- as I thought of plays -- about this material. It's all on horseback. And how do you stage six thousand Indians? So I filed it and forgot it . . ."

Later, of course, he changed his mind -- perhaps when it occurred to him to tell the story in intertwining reminiscences. This is a form that has become increasingly popular lately, and it is hard to imagine a more intelligent, informative and effective specimen than "Custer." But that being said, the obstacles that once caused Ingham not to write this play remain very real, and even in its most engrossing moments "Custer" is definitely low-metabolism theater.

When "Custer" is engrossing, it is partly thanks to the splendid cast the Folger Theatre Group has assembled, and to a stunning production concept executed by director Louis W. Scheeder, set designer Hugh Lester and costume designer Rosemary Ingham (the playwright's wife).

When the curtain rises, the only colors we see are gold, white and a tint midway between sepia and fawn. The cavalrymen and their ladies, against a churning sky, look like figures in a painting by Frederic Remington, and the sky grows darker and moodier as the tale unfolds.

A horse, it's true, would enhance the visual atmosphere considerably, quite apart from the dramatic possibilities. But in fairness to the producers, horses may not be allowed on the Terrace Theater elevators.