I don't want to write about Sen. Charles McC. (Mac) Mathias Jr. as if he had died. All the Republican from Maryland has done is to announce his decision to retire from the U.S. Senate next year, and, contrary to what is so generally assumed in this town, there is life after the U.S. Senate. There is even said to be life outside of Washington. But this, of course, is only hearsay. What interests me about the Mathias decision is neither of these vexed questions, nor even the who-struck-John political details of his recent relationship with his party, a subject that has engrossed many. What interests me is the question of why a man of Mac Mathias' particular enthusiasms should have been consigned so relentlessly over the years to the outskirts of his party.

No one in that party, I believe, will reply that this most affable and humorous of men had a personality problem, as some politically acceptable but personally unbearable figures in both parties do. Again, it is true that he was not shy about bucking party discipline from time to time and going his own way, but then neither have others at the opposite end of the Republican political spectrum been -- far from it. For example, Mathias has opposed and even been crucial in blocking some Republican appointments, most notably that of William Bradford Reynolds to be associate attorney general, but Sen. Jesse Helms of North Carolina has waged campaigns against the confirmation of many Reagan nominees, and somehow he has never been made to seem nearly so much a pariah for his failures of allegiance as Mathias has for his.

So I don't think that the breaking of discipline explains it, and I don't think Mathias' relative liberalism is the answer either. His views and his votes on racial questions have not been al that different from those of a number of other Republicans; and it is worth recalling in this connection that a group including Majority Leader Bob Dole and other Republicans recently complained to the Supreme Court about the weakness of some Reagan administration civil-rights policies.

Of course Mathias is, in this and some other key respects, a liberal Republican. But to say this is, I think, to miss the core theme and motivation of the man. It is to conjure up a kind of modernist sensibility, whereas Mathias is, if anything, its antithesis. He is no cutting-edge-of-institutional- change liberal, no social-science-minded, central- planning pol. On the contrary, the man is almost obsessive in his care for and attachment to tradition, specifically to American historical tradition.

I learned this on a truly freezing afternoon in December almost 15 years ago. I remember the temperature so well because I and a colleague spent several hours riding out to a Civil War battlefield with Mathias in the wreck of a car he drove, which had holes in the floorboards that had been kicked and butted through by the goats he ordinarily transported in it. (When you got in the car and before you ever saw the holes, you knew that goats -- at least -- had been its previous passengers.) We were there because we had been incautious enough to write an editorial in The Washington Post opposing a Mathias effort to double the size of the Antietam National Battlefield park, so that it would include such Civil War landmarks as the probable site of Clara Barton's field hospital.

Mathias insisted that we take this tour. It included, first, a Revolutionary-period farmhouse where we had a very late lunch and restored our failing vital signs with some red wine and at last -- it was pitch-dark by then -- a trek around the icy battlefield. What I remember best is the loving preoccupation of Mathias with every detail of the early-American farmhouse, its construction and furnishings, and his utter familiarity with and enthusiasm for the historic resonances of the countryside we traversed. I almost forgave him the certainty of pneumonia.

In the years since then, I have come to understand that this enthusiasm involves not only traditional Americana -- artifacts and shrines -- but also, and more essentially, traditional American values. It all seems to go together in his mind. Mathias, not to put too fine a point on it, is a Bill of Rights freak. He reads in and about the Constitution. He talks about the Founding Fathers as if he knew them, and in a way, I suppose, he does. Throughout the Watergate time and ever after, when an administration sought to overreach its authority, especially in marauding against an individual or in abusing its powers or encroaching on guaranteed rights, when it lied or snooped or denied due process, you could be sure you would hear from Mathias, that he would be on the phone and on the case. It is his passion. He will nag you to death on it.

Why this should be considered an affront to conservatism -- as distinct from proceeding from a very conservative, traditionalist instinct, which it does -- I will never know. And why it should be considered subversive of Republican policy to demonstrate so thoroughgoing a hostility to the self-aggrandizement of the state is equally hard to understand. The Senate at the moment is hardly controlled by people who are either unsympathetic to these values or hostile to Mathias. Mathias' fellow Senate Republicans -- Dole, Alan Simpson, Richard Lugar, Nancy Kassebaum, Dave Durenberger, Pete Domenici, William Cohen, John Danforth, to name a few -- represent one of the strongest and most respected governing groups the Capital has seen in ages.

You might also think that the more ideological, think-tank right, where so much of the political action and energy are in Washington these days, would have some folks within it who appreciated the antistatist quality of Mathias' passion for the U.S. Constitution. But the truth is that higher- ups in his party have spent a great deal of effort devising ways to keep Mathias from ascending to the chairmanship of the Senate Judiciary Committee, which his seniority brought him to the edge of and for which he had spent a political lifetime preparing. The Republicans, riding high in Washington, should ask themselves how it was that so many of them found this man's American political fundamentalism so frightening and what it says of them that they simply could not find a place for him in their counsels.