It is ironic that Republican control of the Senate after 1986 should be jeopardized by the retirement decisions of two such seemingly contrasting characters as Sens. Paul Laxalt of Nevada and Charles McC. Mathias of Maryland. They appear to be opposites in everything but their vote-getting ability.

But Laxalt and Mathias have more traits in common than is obvious. The liberal easterner and the conservative westerner were born within nine days of each other in the summer of 1922. They both came out of World War II and entered local politics, and both have established themselves as the most successful and only consistent Republican winners in states with heavy Democratic registration edges.

For all the difference in their political philosophies, they are remarkably similar in personality -- which is the reason they are probably irreplaceable as candidates in 1986. There are few senators of either party whose retirement automatically shifts the odds in favor of the opposition taking over the seat.

They are both blessed with a quiet charm and sense of humor that have enabled them to withstand the vanities of the Senate far better than most. They are -- as their constituents, their colleagues and reporters know -- fun to be around.

They are both lawyers whose real love is the land. Mathias is as fond of his farm in West Virginia as Laxalt is rapturous about his ranch. They both know there is more to life than Senate roll calls, which is why they are leaving without regrets while still in their prime.

They are alike in another respect: neither likes to work too hard. They always have taken time to smell the flowers. They enjoy good company and conversation, and they are not afflicted with consciences that require that they be demonstrably improving each shining hour.

It is not an accident that Laxalt has served 11 years in the Senate and Mathias 17 without attaining the chairmanship of a major committee. Mathias was denied the chairmanship of the Senate Judiciary Committee by a conservative power play in 1981 and was relegated to the relatively unimportant Rules Committee chairmanship. But the truth of the matter is that neither has the ego or the drive that goads him to seek power.

But there is an obvious difference in their status as they approach retirement -- a difference that speaks volumes about them and about their party. Laxalt leaves as general chairman of the Republican Party and closest personal and political friend of the president of the United States. Mathias leaves as a figure beloved by his friends and admired for his work on civil rights and environmental legislation, but as a man so far from the levers of power in his party that his only recourse has been to align himself on key issues with the opposition Democrats.

How did this happen? It happened in part because the tides of history have moved the center of gravity in the Republican Party westward and rightward -- increasing the influence of conservatives such as Laxalt and President Reagan and diminishing the sway of progressives such as Mathias and his natural allies among the eastern seaboard Republicans.

While Mathias hitched his hopes to the ambitions of men such as the late Nelson Rockefeller, Laxalt joined forces with Reagan. The rest, as they say, is history. But there is more to it than that, for men shape their destiny as much as destiny shapes them.

The contrast between Mathias and Laxalt parallels the difference between the progressive and conservative wings of the GOP in the past 20 years. It is, in part, a contrast between political effort and political ease.

Laxalt paused in his political career to serve a term as governor. During that time, he put his impetus behind, and his ideological stamp on, a party organization that has made the GOP increasingly competitive in Nevada.

Despite his dislike for long hours, Laxalt traveled constantly -- especially in the West -- during the past decade, rallying conservatives, promising them that someday Reagan would make their dreams come true. And he did.

Meantime, Mathias, as a member of the Senate, did what most progressive Republicans do: he did his own work well, kept his own fences mended and did not worry much about his party. The Maryland GOP is weaker today than it was when Mathias was first elected to the Senate.

The difference between professionalism and dilettantism has been increasingly obvious in the status of the two men. In 1976, when Laxalt was managing Reagan's almost successful challenge to President Ford, Mathias was toying with an independent candidacy for president. It never came to pass.

In 1984, while Laxalt presided at the conservatives' triumphant renomination of Reagan in Dallas, Mathias, typically, was writing an apologetic piece for The Post, headlined "Why Should a Moderate Go to Dallas?" In it he said conservatives were in the saddle because people like himself "do not pay close attention to party affairs. . . . It has been a long-term generational weakness of Republican moderates."

As usual, Mathias had it right. And, as usual, Laxalt had it made.