The sign is in Arkansas, a block from the Texarkana post office that spans the state line: "Edd Hargett" -- no mention of the word Republican -- "in the East Texas tradition." All over the 1st Congressional District you seldom hear "Texas" without "East" before it.

Yet what seems an intensely local contest is really a test of regional party realignment that could change the balance of power in Congress. "East Texas" is political shorthand for a set of attitudes: a consensus on national issues and also on the values of small-town life and traditional religion in a South whose most conspicuous growth recently has been in metropolitan areas.

This is ancestral Baptist and Democratic country -- adjacent districts produced Sam Rayburn and Carl Albert, and the yellow-dog Democratic 1st stuck with Hubert Humphrey in 1968 and Jimmy Carter in 1980. Republican Hargett has a chance here because of the rise in Republican Party identification in the South over the past 18 months, but also because he has genuine local roots and chose to return here when he had other choices.

Hargett was born on a farm in Cass County, mostly cattle country now. The leaves are sodden after June rains; black-eyed daisies thrive on the roadsides. As quarterback he led Texas A&M to victory in the 1968 Cotton Bowl -- a moment relived in his first wave of TV ads. He played in the NFL (New Orleans, Houston) and the World Football League (Honolulu, Shreveport).

When the WFL folded, and he and his wife returned to the Cass County farm they'd bought, and he took the job his father helped line up as chief engineer at the local electric coop. Quite a contrast: the world of Astrodome skyboxes and Gallerias, and the county seat of Linden, with a couple of old bleached-brick buildings restored around a square and red dirt side streets a block away. "I didn't want to raise my family in the big city," he says. "I like the idea of a smaller community where you know people and people know you."

Quick to laugh and almost shy in person, Hargett isn't as aggressive as you'd expect of a candidate who lifted himself up to run for high office. But then he didn't do much of the lifting.

Phil Gramm, the Boll Weevil Democrat-turned- Republican who was elected to the Senate in 1984, created this vacancy by appointing Boll Weevil Sam Hall to a federal judgeship; he helped hire top consultants Lee Atwater, Lance Tarrance, Roger Ailes; he and the national Republican Party will raise perhaps $750,000 and are buying TV time in Dallas- Fort Worth as well as locally. They hope, and the Democrats fear, that Hargett will get the 50 percent needed to win a multi-party primary June 29 without a runoff.

Any Hargett victory would be a revolution of sorts. Republicans are already competitive in the metropolitan South; but Democrats still hold almost all offices outside the metropolitan areas. A Hargett win translates a theoretical jump in party identification into a concrete political threat in 40 nonmetropolitan southern seats held by Democrats now. That could ultimately cost the Democrats their House majority and could more quickly deprive their leadership of working control.

Such things are not much on the minds of former district attorney Jim Chapman and state Rep. Sam Russell, the Democratic contenders. Their fathers both served in the legislature and established small-town law practices. They're proud of raising something like $200,000 from their own funds and their communities. They talk a lot about qualifications and conservatism.

"Everything Jim Chapman is involved with, he ends up runnng," says Chapman, and boasts that as D.A. he made Dallas' Henry Wade, famous for his 1,200-year sentences, "look like a sissy." Russell's brochures identify him as a proven legislator and "a Democrat, but in the conservative East Texas tradition." Why Democrats? Chapman feels Texas Republicans such as Gramm "are so inflexible;" Russell says, "I just feel more comfortable as a Democrat."

But things that would have made one of them an easy winner in the past don't work so well now. The only Democratic issue they seize is Social Security, and Hargett on TV and in forums remembers that "my mom and dad depended on Social Security," and swears he'd never cut it.

For all his lack of experience, Hargett is better than the veteran pols at addressing issues in the language of ordinary people. His second wave of TV spots hammer home succinct, clear messages on Social Security (no cuts), education (basics), and school prayer. Waiting his turn patiently at the forum, he's learned to make his points clearly and get cheers. He knows his facts and figures and can adroitly insert a saving clause into a sentence to avoid trouble.

If Hargett wins, and he has a solid chance to do so, he will have proved that a Republican can be part of the "East Texas tradition," and that a handpicked Republican candidate whose message is adapted to his native terrain can beat the aggressive self-starter Democrats who have always won most rural southern districts.