Sen. John Tower, who for 17 years has remained the only Republican elected statewide in Texas over the past century, is now running in his most harrowing reelection campaign yet, one that could well end with his defeat.

Always the accident in Texas one-party politics, Tower has seen two-term Democratic Rep. Robert Krueger make consistent gains and even overtake him in the polls.

A generally conservative Democrat, Krueger has followed a careful course - conservative on most issues, liberal on a few - that has apparently held onto large numbers of liberals and conservatives who abandoned one or the other of Tower's Democratic opponents in past election.

The result is a narrow Krueger lead in the only statewide, nonpartisan poll taken here so far. But so close is the race that the plooster himself called it a toss-up.

Moreover, Krueger has managed, as past Tower opponents haven't, to raise enough money - perhaps $300,000 - for a campaign-end media drive that may use equal-time laws to force Tower's commercials off the air waves and his on.

But what is also at stake here are the political futures of two men - the earthly articulate Tower, who is one of the most influential of Republican senators and among the most senior of them all, and the Elizabethanly eloquent Krueger, who is often said to hold national political ambitions if he can just win the Senate seat that was once held by the late President Johnson.

These stakes have produced gut-level campaigns that have not yet had to resort to important issues. They are campaigns that have prompted an Austin editorial cartoonist to create a parlor game called "Texas Politics."

This is a box of dirt for $30 - you just add water and sling.

Tower accuses Krueger of having spent most of his entire life "overseas or in the East" studying and teaching, a serious charge in Texas where the view is that all kinds of beliefs can afflict a man once he is beyond the watchful Eyes of Texas.

He has questioned Krueger's lack of military service, called him a "Little Lord Fauntleroy" and spoken darkly of Krueger's bachelorhood.

for his part, Krueger aides have mailed out charges to newspapers editors saying that, in essence, Tower is a lecherous drunk, a move that led to Tower's widely publicized, if little explained, refusal to shake hands with Krueger at a press club appearance here.

"Sigh," Houston Post columnist Lynn Ashby writes of the two men. "It's a real downer. Out of 12 1/2 million Texans, is this the best we can do?"

Regardless of whether they are the best, they are both expensive. Tower expects to spend $4.5 million in his reelection campaign, and Krueger expects a $1.4 million effort for the general election, following the $1.1 million primary election effort. Both men have received contributions from the same special interest groups - particularly those in oil and gas - and some groups are walking both sides of the street by contributing to both candidates.

On many issues, both Tower and Krueger play the same conservative political Muzak, the soothing background sounds that attack deficit spending, big government, national defense and intrusive regulation.

But Tower, standing 5 feet 5 inches tall in his cowboy boots with riding heels, breaks above those background sounds by criticizing Krueger's vote for the labor revision bill to help Big Labor, his vote to give the District of Columbia two Frost Belt senators to cancel Texas' votes.

Krueger accuses Tower of being a nay-sayer who has been ineffective and insensitive on behalf of all Texans. He says that no major legislation bears Tower's name and notes that it was he, Krueger, who moved the deregulation of natural gas prices to ultimalte approval by the Congress.

A a part of the majority, Kreuger, says, he could be more effective. To which Tower raises the possibility of a Republican president in 1980 and says Texas should have representation in both national parties.

But it could all get down to the minority voters, the blacks to a certain extent, but primarily the Mexican-Americans, who may very well swing this election, if they turn out in great numbers.

Tower claims that he has always gotten 35 percent or so of the Hispanic vote, a figure some analysts argue is too high. But Krueger, with the endorsemet of key Mexican-American leaders, draws 50.5 percent of the Mexican-American voters and Tower gets 26.9 percent in the Texas Monthly magazine poll. The rest are undecided or favor a third-party candidate.

It was that poll that more or less rocked the state. It showed that as of early October, Kruegen had moved ahead of Tower 42.7 percent to 38.9 percent in poll of 1,000 Texans. A little more than 17.3 percent was undecided.

Perhaps most important is the nearly two years Krueger has spent seeding the state with personal appearances, extolling the values and virtues of tiny towns, where he now hopes to harvest votes.

He has been to towns that have not seen a U.S. Senate candidate since 1948, when Lyndon Johnson dropped out of the sky in a helicopter, gradly pitching his Stetson from the chopper in bold arrival. (An aide was assigned to retrive the hat for use at the next stop, or so the story goes.)

So crucial is the Mexican-American vote to Kruger that one of his campaign aides, Marc Campos, met with the La Raza Unida Party Senate candidate, Luis Diax DeLeon, to discuss DeLeon's possible withdrawal from the race to help Krueger.

After the meeting, DeLeon charged Campos with offering financial inducements to get out, but Campos says he ended the meeting when DeLeon demanded concessions in exchange for a withdrawal. The incident has been referred to the FBI for investigation.

Whatever the seriousness of those allegations, they have been overshadowed by Tower's refusal to shake hands with Krueger. This is a state where the principal business is Doing Business and deals and dealers start and finish with a manly grip.

Tower's refusal came after the Krueger staff distributed a newspaper column by an obscure right-winger in Tennessee that referred to some unnamed senator "who ranks high in the U.S. Senate and low in the ranks of nice women who avoid getting on Senate elevators with him."

"That's the man, I'm told," columnist Tom Anderson indulged, who "comes into town for a speech and tells his escort on the way to the hotel, 'get me a fifth of whisky and a woman.'"

Although no one was named in the column, Kruegerites named the senator as Tower."

It is unknown what the effect of the non-handshake will be. Krueger claims it confirms the view among Texans that Tower is aloof and elite. Tower says that at most it may crystallize previous feelings. Neither feels it will be decisive.

So this year, with one out of every six voters undecided, according to the Texans Monthly poll, voters perhaps feel a columnist Lynn Ashby did when he wrote, "We cannot sidestep the problem. It is unfair to cop out and then to complain later. But, Lordy, does it have to come to this?" CAPTION:

Picture 1, REP. ROBERT KRUEGER, . . . leads in nonpartisan poll; Picture 2, SEN. JOHN TOWER, . . . harrowing reelection campaign; Picture 3, Krueger, campaigning in Laredo, addresses a largely Hispanic audience; Picture 4, Tower relaxes during airport-to-airport politicking in closing days of the race, Photos by Bill Curry - The Washington Post