SEN JAMES B. ALLEN of Alabama, who died suddenly on Thursday, was a master of the Senate rules. That is the first thing to be said of Mr. Allen, and it is no mean praise. He did not merely learn Jefferson's parliamentary manual; he absorbed it and employed it more doggedly, shrewdly and creatively than any other senator in years. In the era in which the all-night Senate filibuster went out of style, Sen. Allen substituted tactical skill for oratorical stamina. He was constantly devising new - but impeccably precedented - ways of sustaining debate, blocking legislation he opposed, and defending the conservative positions that he held tenaciously.

He was effective - far too effective, from the liberals' point of view. At various times he managed to block or delay campaign-financing legislation, voter-registration bills, civil-right measures, tax changes and much, much more. On the Judiciary and Rules Committees, he was always a factor to be reckoned with. On the Senate floor he was a formidable, independent force.

In short, Sen. Allen was an old-style Southern conservative. He was akin to that generation of very adept, very strong-minded and very parliamentary Southern Democrats who ruled the Senate not so long ago. He didn't merely love the rules; he relished the institution and its traditions of courtesy, precedence and rich debate. It was no accident that, for all their disagreements over issues, Mr. Allen and Majority Leader Robert Byrd developed a generally good working relationship. One would expect that of two "inside" senators with high regard for details and proprieties.

Mr. Allen's death surely diminishes the power of the Senate's conservatives. But liberals, too, may miss him, for he did impose a kind of discipline on the Senate's life. Every sponsor of a bill knew what he might have to contend with; outrageous measures were called up less often, and fewer corners cut, because Mr. Allen was there. Now other senators of both parties have learned some of his tactics - there has been ample evidence of that. But no one uses them quite as predictably or calmly or consistently. With Mr. Allen gone, there may be fewer parliamentary sieges in the Senate, but lots more guerrilla warfare. For the institution, that is not necessarily a gain.