IN THE "WORLD'S greatest deliberative body" it takes no special talent to be recognized by colleagues as "the distinguished senator." For any of them to mean it and for voters to so thoroughly endorse the judgment is something else again. But the independence of Charles McC. Mathias Jr. long ago earned him rare respect as a public servant. His is not a record of grandstanding or of trashing his own party for points. What the Senate will lose at the close of its business next year is a man whose sense of public service is deeply rooted in the Constitution he reveres and defends with emotion and courage.

Sen. Mathias has been a great defender of civil rights and individual liberties. He has been a tireless protector of his state's interests, including its natural resources, which he seems particularly to treasure. He was also notable for being one of the first Republican politicians to recognize and criticize the Nixon administration's misconduct in Watergate: "bugging, wiretapping, breaking and entering are aggravated crimes when used to pervert a national election."

This latter commitment to the balance of powers and the government as constituted explains the senator's interests in the operation of Congress: campaign spending, the seniority system, open committee meetings, full disclosure by members of Congress of their sources of income. Again yesterday, this larger view was evident in answer to a question about the cost of running again: was it a factor? Not the thing in his case, he replied, though "it costs much too much to run for every public office today," which "is a crisis of liberty -- and I think that's not an overstatement."

"When I was elected to the Congress in 1960," he said yesterday, "we were a nation divided by the barriers of law, custom and practice. Today, there is no legal barrier of any kind between Americans of differing race and creed. That is change in its most positive form. I am proud to have played a role in that peaceful revolution." Sen. Mathias played a very large role in that revolution, and he will be missed.