JOHN L. McCLELLAN, the Arkansas Democrat, was nearing the end of his fifth term in the Senate when he died yesterday at the age of 81. So, his career spanned some enormously important - and occasionally convulsive - changes in the country's public life, and it also brought him the entitlements and rank that go with longevity in office: Sen McClellan was chairman of the Senate Appropriations Committee when he died, and he had previously been chairman of the Senate Committee on Government Operations. He had played a prominent role in the civil rights battles of the postwar years, the Army-McCarthy hearings, the labor and crime legislation that took shape in the past two decades.

In much of this we had found ourselves on the opposite side from John McClellan, especially where racial and civil-liberties questions were concerned. But none of that alters our view that Sen. McClellan was a man of personal dignity and fairness, who did not abuse his power in the Senate or seek to close out the views of those who disagreed with him. And wherever others, ourselves included, may have fetched up concerning his principal interest - i.e., the creation of conditions that would restore for authority in this country - no one could deny the relevance of this preoccupation to our public life in recent years. One didn't have to share Mr. McClellan's conclusions on how to deal with crime to share his outrage at the organized depredations of the labor and Mafia racketeers.

Sen. McClellan does leave one indisputably monumental achievement: the enormous and enormously complex codification of the nation's criminal laws on which he had worked for many years and which he had not so long as managed to accomodate to the views of some of his critics, such as Sen. Edward Kennedy. The negotiated result, now before the Congress, is legislation of great stature and importance - truly of landmark quality.

We would mention only one further aspect of the senator's record.That is the sad and terrible record of personal tragedy that befell him as a father three times bereaved in a life that was stark and Job-like in its accumulated ordeals. John McClellan fought back, mastered his sorrow, overcame the temptation to self-pity and, with hard work, built a new life. This is a town where accomplishment is often measured in terms of legislative monuments alone. But we put Sen. McClellan's personal strength in the face of adversity at the top of the list of his life achievements.