SOMEWHERE in the gadfly memories of most journalists there are favorite quotes that validate the curious business of being a reporter. One favorite is a fragment from Philip Graham who said that journalists accomplish "the impossible task of providing every week a first rough draft of history...."Contrary to this is the memorable laceration from one Spiro Agnew denouncing journalists as "an effete corps of impudent snobs who characterize themselves as intellectuals." A major exhibit to help form or change your own conclusions about journalists has been provided by the Library of Congress in cooperation with the American Society of Newspaper Editors (ASNE). "The American Journalist: Paradox of the Press" opens to the public today in the lobby and second floor of the Christian Science Publishing Society and continues until Sept. 18. The exhibition, first seen at the Library of Congress earlier this year, was made possible by a $325,000 grant from the Gannett Foundation. True to his profession, Loren Ghiglione, the co-curator of the exhibit and editor of The News in Southbridge, Mass., has avoided a conflict of interest. In the preface of his splendid book accompanying the exhibit he notes that he "has refrained, in the book and the exhibit, from noting the achievements of any Gannett journalists." Score points for journalism ethics, and applaud Mr. Ghiglione and his co-curator, Dr. David F. Halaas, for mounting an earthy, contentious, fascinating exhibit. It has artifacts, such as Ernie Pyle's typewriter, Margaret Bourke-White's camera, Walt Whitman's spectacles, old photos, dashes of history, fun, and seriousness, and a smattering of front pages. It might have been subtitled "the rascals and beavers of journalism." Behind the First Amendment that protects journalists and behind the ritual grind of putting out a daily or a weekly, journalism has hatched some wonderful characters. Some were rascals who played fast and verbose with the truth while others pursued the truth with dogged beaverness that toppled presidents. The exhibit wisely focuses on these "rascals and beavers" with appropriate forays into the issues of journalism, such as liberal journalism in the South during the height of Civil Rights marches. Part 1 of the exhibit catagorizes journalists as street reporter, persuader, crusader, investigator, exploiter, entertainer, war correspondent, and broadcast journalist. Part 2 tackles the "the journalist of fiction." For a genuine street reporter, consider Meyer Berger of the New York Times, who went from police reporter to writing a column. What made Berger different was the "poetry" of his prose and the speed of his writing. In 1949 a gunman shot 13 people on the streets of Camden, N.J. Berger retraced the steps of the crime spree, interviewed 50 people, and then wrote a 4,000-word article in two and one-half hours. Berger got a Pulitzer Prize for local reporting, and he gave the cash to the gunman's mother. For sheer tenacity consider Edith O'Keefe Susong. A divorced woman with two children, Susong took over a faltering weekly in Greeneville, Tenn., in 1916. She did everything: wrote the articles, sold ads, helped run the press, took the papers to the post office. Her competitors scoffed at her. Eventually she bought them out and started a daily, the Greeneville Sun. When she died 58 years later her paper had one of the highest circulation/household ratios in the country. For a journalism artifact, stop for a moment in the exhibit and consider Bob Woodward's notebook, the very notebook in which he wrote the first lines noting that five men had broken into the Watergate complex. He scribbled the lines when the city editor of the Washington Post called him. It was the beginning of the end of Nixon's presidency. What the displays of the exhibit prove is the force of journalism, the dynamics it creates by being so close to the issues of the day. At best it takes history by the hand, trying to explain what is happening. At worst, as the exhibit demonstrates, journalism can stumble badly, look ridiculous, and besmirch the wrong people for the wrong reasons. * The exhibit travels to the Dallas Public Library Sept. 30-Dec. 15. It is planned to make two more stops - in the Midwest and West Coast - before it reaches the Strong Museum in Rochester, N.Y., Aug. 21, 1992-Oct. 18, 1992.