The story of how Honest Abe's gentle face became a national image; The Lincoln Image: Abraham Lincoln and the Popular Print, by Harold Holzer, Gabor S. Boritt, and Mark E. Neely Jr. New York: Charles Scribner's Sons. 234 pp. $35.

WITH images of politicians so pervasive during this election year in the United States, it's hard to imagine a time when campaigns were conducted without television or even newspapers capable of showing photographs of the candidates. Yet in 1860, when Abraham Lincoln was nominated for the presidency, few people even knew what he looked like.ck

In ''The Lincoln Image,'' authors Holzer, Boritt, and Neely zero in on this period of Lincoln's career to trace the role print imagery played in the making of a president.

Their interesting and meticulously researched book is the companion to a federally funded traveling exhibition now on display at Gettysburg College in Pennsylvania. Opened on Feb. 12, the 175th anniversary of Lincoln's birth, it continues in Gettysburg until Sept. 16. More than 100 black and white photos and engravings from the exhibit, some reprinted for the first time, are to be found in the book. And the text is full of interesting bits of history.

Some readers will be surprised to learn, for example, that Lincoln didn't even attend the 1860 Republican National Convention in Chicago. In those days a candidate was considered suspect if he campaigned too vigorously in his own behalf, the authors point out. Most of the delegates who voted for Lincoln had never seen him. Yet his backers were prepared.

Even though the candidate had no photographs in his possession to give them, they were able to find one in New York. They had copies made of it, and, at the exact moment when the dark horse candidate's name was put forth for nomination, they released a shower of handbills imprinted with Lincoln's likeness from the balcony. The gesture met with a roar of enthusiasm from the delegates. After the nomination, a life-size portrait of Lincoln, which had hung in a side room of the convention hall, was brought to the stage and displayed to the 11,000 cheering Republicans in attendance.

The authors also sketch in enough of the 19th-century milieu to give the Lincoln phenomenon perspective. This was an era, in fact, when people were infatuated with prints and photographs, the authors explain. Walls in Victorian parlors were nearly covered with engravings and lithographs. And, since a favorite sport of the era was politics, even likenesses of candidates were often found in homes.

As the 1860 campaign progressed, Lincoln's backers had problems in selling their candidate, the authors note. He was an unknown; he was homely; photographs of him were quite rare; and he was outspoken in his controversial stand against slavery. As a result, the authors point out, Lincoln's backers seized on various images, among these Lincoln as a ''rail splitter'' and an ''honest man.''

But anti-Lincoln cartoonists also had a field day, the book shows. One cartoon of the day features Lincoln straddling a single rail (the Republican platform) carried by a black slave and a white Republican. Inclusion of more of such cartoons would have been interesting and instructive.

To the authors' credit, however, they do provide ample illustration of how photographs and paintings evolved into engravings.

As the demand for Lincoln images grew, photographers and painters made their pilgrimages to Springfield. They apparently had their difficulties, though, in capturing the subject. Rarely did the people who knew Lincoln feel that a photograph or painting depicted him accurately.

''The Lincoln Image'' is divided into sections which focus on the campaign, the presidency, the Civil War years, and the assassination and its aftermath. We learn that prints produced after Lincoln's death undoubtedly aided in making him a national hero, second only to Washington.

Especially informative are the explanations accompanying each of the illustrations in ''The Lincoln Image.'' It was common, the authors explain, for engravers to fit a new face onto an old piece of work in order to speed up the process. Anyone who has puzzled over the oddities and inaccuracies of 19 th-century prints can better understand the work of that period through this volume.