MONTEREY, Tenn., Oct. 23— In rural, rugged middle Tennessee, the race for one State Senate seat has been altered by a single bullet, and the surviving candidate in District 15 will watch the outcome from behind a jail door.

Tommy Burks, the popular Democrat who was expected to win re-election easily, is dead and buried. Mr. Burks, 58, was shot in the forehead on Monday at his 1,000-acre hog farm outside the little town of Monterey, not far from his pumpkin patch.

The crime left just one name on the ballot in the Nov. 3 election, that of the Republican challenger, Byron (Low Tax) Looper, who was arrested this morning and charged with the murder of Mr. Burks.

Because under state law a dead man may not appear on the ballot, but a man charged but not convicted of a felony may, only Mr. Looper's name will confront shaken citizens in voting booths.

Suddenly, negative television advertisements, name-calling and mud-slinging do not seem so bad, people here said.

''It's hard to believe,'' said Doug McBroom, the Putnam County Executive and a Democrat who, like others in his party and in an embarrassed Republican Party, said he will support the write-in candidacy of Charlotte Burks, the incumbent's widow, in her last-minute campaign for his office.

''This is supposed to be a system of the people, for the people,'' Mr. McBroom said. ''Something this bad, it strikes at the heart of that system.''

Others were more blunt.

''If he did it, they should string him up,'' said Patricia Hassler, who owns an antique shop in Monterey, a town with 2,872 residents.

Mr. Looper, 34, who had his middle name legally changed from Anthony to (Low Tax) to reflect his political philosophy, was in the Cumberland County Jail today, awaiting an arraignment, as people from wide places in the road, places like Hanging Limb, Muddy Pond and Lovejoy, asked themselves if simple politics was enough to motivate a murder.

''We feel real comfortable we've got the right person,'' said Sheriff Butch Burgess of Cumberland County, although he and other investigators would not say what evidence they had linking Mr. Looper to the crime, or what motive -- beyond political gain -- he might have had.

In fact, no one has an explanation, But people here said that Mr. Looper's political career, still new, had seemed self-destructive from the start.

Mr. Looper, the controversial Putnam County Tax Assessor who is under indictment on charges of theft and misuse of office and is the defendant in a paternity suit, was arrested at his home in Cookeville this morning about 1:15 by a deputy sheriff who was staking it out.

Mr. Looper had last been seen on Sunday night, the night before Mr. Burks's body was found in the cab of his pickup truck, a small bullet hole in his forehead. As late as on Thursday night, investigators had refused to call Mr. Looper a suspect, saying they were only searching for him to question him.

But around here, where Mr. Burks made a bounty of friends and allies in three decades in state politics, people were suspicious early on.

It was Mr. Looper's absence, more than anything, that made people suspicious. Four days passed without a word from him. If he had nothing to do with the crime, then why was he in hiding, people here wondered.

''It doesn't look good,'' said Jack Phillips, the Mayor of Monterey.

''It sure doesn't,'' said Clinton Wright, who was visiting with the Mayor.

Mr. Phillips, like others here, wondered why Mr. Looper never called the Burks family to offer sympathy. At least, people here said, it was bad manners. Mr. Looper's lawyer, Lionel Barrett of Nashville, was apparently the only person who spoke with him during his absence. Mr. Barrett said he spoke with his client again today but offered no insight into where he had been or why he had been missing.

Meanwhile, Democrats -- and some Republicans who said they disapproved of Mr. Looper's behavior in office -- drafted Mrs. Burks to run.

''Write-in campaigns are hard,'' said Mr. Phillips, ''but I think she can win.'' He, and others who know District 15 politics, say they doubt Mr. Looper can be elected. Mr. Phillips has donated his mayoral salary, all $500 of it for this year, he said with a smile, to Mrs. Burks's election.

All over Putnam County, people wave placards at the roadside to urge support for the write-in campaign.

Until the murder, it had not been shaping up as much of a race. Mr. Looper's campaign attracted little attention, and there seemed no bad blood between the candidates, people here said.

On one side of the election was the gray-haired Mr. Burks, who people here say they cannot remember ever seeing in a suit and tie.

''You'd see him in his rubber work boots, after slopping his hogs,'' Mrs. Hassler said. ''He was one of us. He was a good man, probably the only honest one we had.''

His politics, in the State House and Senate, sometimes put him at odds with his own party, and sometimes aligned him with Republicans. He fought against abortion and gambling, and for victims' rights.

He made his most controversial stand two years ago when he sponsored a bill that would have required the dismissal of teachers who taught evolution as fact. The bill failed.

But here in his district, he was far from controversial. Most people thought as he did, Mrs. Hassler said. He voted their will, she said.

On the other side was Mr. Looper, who, even before the events of this week, seemed in deep trouble.

Born in Tennessee, he was a student at West Point until, he said, a knee injury forced him to take an honorable discharge in 1985, The Associated Press reported. He moved to Georgia, where he ran unsuccessfully for the state Legislature at 23. He was a legislative aide, then reportedly lived awhile in Puerto Rico.

He won his job as tax assessor in what many people here described as a negative campaign two years ago, promising to fight for lower taxes.

But quickly his career was marked by accusations of scandal, including charges that he had offered tax breaks to land developers in return for political contributions. The accusations led to Mr. Looper's indictment in March on charges of theft and misuse of office -- charges he denied. He is awaiting trial.

He is also being sued by a former girlfriend who said he fathered her baby and tried to transfer ownership of her home to his name by faking a deed.

In a statement after the woman filed suit, he said that she ''left me with heart palpitations, a small box of memorabilia and a red G-string.''

His manner bothered many here.

''His attitude was that we're all dumb, and he was here to save us,'' Mr. McBroom said. He talked down to Democrats, and promised favors to his Republican constituents, people here said.

He dismissed employees and insulted co-workers, courthouse workers said.

''He thought he was the smart one, but he kept getting caught,'' Mr. McBroom said.

Mr. Looper said he was being persecuted because he was a Republican, in a county dominated by Democrats.

Finding people to speak up for him is hard. One woman in Cookeville acknowledged voting for him, but begged not to have her name used in connection with him.

His race for the State Senate seemed to make no sense. He ran unopposed in the primary, because State Republican Party officials did not believe anyone could unseat Mr. Burks. The party did not endorse him because of his political history, state party leaders said this week.

It is possible, but unlikely, that he could win.

Write-in candidates almost always fail, but voters here said this is an unusual case.

''I think she will win,'' said Mr. Phillips of Mrs. Burks, who has had little to say publicly about her campaign. The voters, Mr. Phillips and others here said, will vote their broken hearts, and their outrage.

Photos: Tom McClatchie, right, and Marshall Cox of the Putnam County Volunteer Fire Department searched for the gun used to kill Tommy Burks, a Tennessee state senator, near where his body was found on Monday. (Associated Press); Tommy Burks, above, a Tennessee State Senator, was killed on Monday and Byron (Low Tax) Looper, top, his challenger, was arrested yesterday in the crime. (Associated Press) Map of Tennessee showing location of Monterey: A bullet altered a State Senate race in the small town of Monterey.

Fred Thomas Burks