Lincoln Steffens was approached one day by an earnest history professor. Tell me, the professor said, how you happened to start muckraking. Share your knowledge on an important chapter of American history and in so doing cast light upon the rise and run of social movements.

Steffens replied that he wasn't the original muckraker. "The prophets of the Old Testament were ahead of me," he said wryly, adding that so were countless American writers and reformers of the last century. He then explained:

"I did not intend to be a muckraker; I did not know that I was one until President [Theodore] Roosevelt picked the name out of Bunyan's 'Pilgrim's Progress' and pinned it on us; and even then he said it did not mean me. Those were innocent days; we were all innocent folk; but no doubt all movements, whether for good or for evil, are as innocent of intentions as ours."

And that is how it started.

We are indebted to two judges on the bench of the U.S. Court of Appeals for the District of Columbia for calling public attention to the part muckrakers played in our history:

George MacKinnon, a one-term Republican congressman from Minnesota, was described as a conservative with no judicial experience when he was appointed to the bench here 15 years ago by President Richard M. Nixon, for whom he had worked in political campaigns. Antonin Scalia was described as a "well-known conservative scholar" from the University of Chicago law school when President Reagan appointed him to the bench three years ago. They are the ones who have dredged up memories of the muckrakers and drawn lessons for the future from those social and journalistic reformers, or crusaders, if you will, of decades ago.

The judicial allusion to muckrakers and the problems they create came in the judges' decision last week to reinstate a jury verdict that The Washington Post had libeled the president of Mobil Corp. Now granted, it seems self-serving for someone on the payroll of this paper (and a longtime, card-carrying, second-generation member of the press as well) to say what a terrible decision theirs was and what an appalling precedent it could set. Besides, the lawyers will be arguing the merits of this case for some time and the final judgment has yet to be rendered.

Yet, this decision cries out for public scrutiny, debate and understanding. For, if my reading of it is correct, the implications are startling. They are alien to the experience of the way the press has performed historically in this country; they cast aside the reasons why the press was granted such extraordinary legal license to examine and report, criticize and praise, challenge and dissent on areas encompassing the widest range of American life; they are a direct threat to the philosophical assumptions and constitutional guarantees underlying the First Amendment, the bulwark against abridging freedom of expression for every American, whether a member of the press or not.

Muckrakers like Lincoln Steffens at the turn of the century exposed municipal corruption, campaigned for good government, prodded the conscience of the nation by calling attention in print to abuses in political and corporate life, spurred the climate for reform and the progressive era that followed, put a definite imprint on the passage of laws that are still standard in this country, and then the muckrakers passed into history. The judges linked that old history of journalistic practice to what they see as wrongs in the present era of so-called investigative reporting -- and condemned them both en masse. As their dissenting judicial colleague, J. Skelly Wright, wrote:

"The notion that a policy of muckraking and hard-hitting investigative journalism is somehow evidence of actual malice is deeply troubling, contrary to the nation's tradition of a free and aggressive press, and entirely unsupported by precedent."

Wright, in my view, brilliantly went to the heart of the matter by saying:

"This conclusion represents a sharp departure from the principles of free and vigorous discussion that have been the touchstone of First Amendment jurisprudence. It is a conclusion fraught with the potential to shrink the First Amendment's 'majestic protection' . . . .

"In our society speech may be controversial and contentious; words may be intended to arouse, disturb, provoke, and upset. For a primary 'function of free speech under our system of government is to invite dispute. It may indeed best serve its high purpose when it induces a condition of unrest, creates dissatisfaction with conditions as they are, or even stirs people to anger.'

"Muckraking -- a term devoloped when writers like Lincoln Steffens, Ida Tarbell, and Upton Sinclair relentlessly exposed pervasive corruption -- may be seen to serve that high purpose even if it offends and startles; so, too, hoping that readers will react in colorful terms to front-page stories fits comfortably within the traditions of a free press and a nation that has nothing to fear from an aroused citizenry. As Justice Brandeis observed, 'Like the course of the heavenly bodies, harmony in national life is a resultant of the struggle between contending forces.' "

That kind of language may sound too old-fashioned for today's ears, though I find it stirring. And certainly the current climate in which the press is continually accused of having a "negative news" cast of mind has had an adverse impact on public attitudes. But if last week's decision serves to introduce this generation of Americans to the role the muckrakers played in our history and to such journalists as Lincoln Steffens, the mentor for Walter Lippmann, among others, it will have been worthwhile.

Besides, it can't be all bad if that decision forces people to read that wonderful book, "The Autobiography of Lincoln Steffens." There you'll find these words:

"As a journalist, I was keen to deal with certain sayings which men used to express their unformed thoughts and save themselves from the labor of thinking out what they meant. 'Don't knock; boost' was one of those thought-savers. It was the grafters' answer to all muckraking, and, passed on to the absent-minded citizens, we heard it everywhere."

Dangerous thought. It ought to be banned.