The retirement of Sen. John G. Tower of Texas is no more an ordinary political event than was his first election. His election was a landmark in the emergence of the conservative movement in America and the rise of the Republican Party in the South. It will not be a shock if his surprise announcement last week that he is stepping down at age 58 turns out to be an equally important signal.

My recollection of that June day in 1961, when Tower was sworn in as the first Republican senator from Texas and the Deep South in the postwar era, is that a large contingent of congressional Republicans met his plane at National Airport and escorted him to the Capitol for the ceremonies.

The clips say there were at least 200 Texans on hand, wearing "Viva Tower" buttons. Senate minority leader Everett McKinley Dirksen, never one to underplay a scene, said Tower's victory was "not unlike the election of Lincoln in 1860."

Today, when Republicans hold Senate seats in Florida, Georgia, both Carolinas, Virginia, Alabama, Mississippi, Tennessee, Oklahoma and Texas, it is hard to recall what a sensation it was to have a Republican from the South. And what a senator!

A few of us had caught glimpses of the 35- year-old professor during his quixotic campaign in the autumn of 1960 against Sen. Lyndon B. Johnson. LBJ had craftily had a law passed allowing him to appear twice on the Texas ballot that November, once as a candidate for reelection and once for vice president.

But not until Tower came to the Capitol did we realize what a tiny, bandbox figure was to be succeeding the lanky Johnson--for what an implausibly dapper and polished English-looking gent was now speaking for the brawny Lone Star state. (In later campaign years, Roger Mudd's pieces on Tower--focusing lovingly on his English cigarettes in their elongated holder, his gold lighter and cuff links--became television classics.)

Tower was lucky to win. In the election to pick Johnson's successor, an impossibly overloaded primary yielded as the Democratic candidate one "Dollar Bill" Blakely, a colorless conservative who had been appointed as the interim seat-warmer by Gov. Price Daniel. The liberal Texas Democrats, with their usual shrewdness, decided Tower would be easier to beat for reelection in 1966 than Blakley, so they stayed home or voted Republican in the special election. And Tower got in.

But there was more to it than that. Tower had stumped around Texas with Sen. Barry Goldwater, preaching a free-enterprise, anti- big-government philosophy that was a direct challenge to the Kennedy-Johnson version of the welfare state. Goldwater was just beginning to convince some Republicans that his uncompromising conservatism might work at the polls. When Tower won in LBJ's home state, the theory became a passionate conviction for millions of conservatives and Republicans.

As the years went on, we learned that Tower was less a fluke than he first seemed. He was a resourceful politician who hired bright staff people, many of whom have gone on to useful careers of their own. Earlier than most politicians, he entrusted his organization and fund- raising to capable women.

Following him around east Texas in one campaign, I had the impression that his father had served every Methodist church in that part of the state. Everyone Tower met seemed to be a former choir member and, remarkably, Tower acquired a kind of choirboy innocence of his own.

That night, in the bar, he was quite a different fellow, holding court for the ladies and the reporters with tales of how he won Mexican- American votes in the Valley towns, "just giving 'em the old Amigo bit."

I am not privy to his personal reasons for quitting at the end of this term, rather than seeking reelection in 1984. It is said that he, like Majority Leader Howard H. Barker Jr. (R- Tenn.), is "fed up" with the frustrations of the Senate.

Tower is cynical about many issues, but not national security. He wanted to be secretary of defense in President Reagan's first Cabinet, and maybe he will get the job if there is a second term. That is about the only thing that would reconcile Texas to losing the chairmanship of the Senate Armed Services Committee.

The gaps left by Baker's and Tower's retirement plans make the Republicans increasingly vulnerable to a Democratic takeover of the Senate next year. Tower's decision may signal more than that. The man may look small, but all his political life his actions have produced large waves. His quitting will probably do so too.