There's a humdinger of a political fight going on over the state agriculture commissioner's job in Texas, but you can't digest it without some background.

The Democratic primary scrap between incumbent Reagan V. Brown and Jim Hightower is front-page stuff in Texas, where it's being taken seriously. Truth be known, state agriculture commissioners are not often page one personalities unless they're involved in some kind of zaniness.

For example, Jim Buck Ross of Mississippi is storied for the fleet of airplanes he accumulated to spray poison on fire ants. A sexual harassment hearing last year involving Kentucky's Alben W. Barkley III got statewide TV coverage.

But James Graham of North Carolina often gets more votes than gubernatorial candidates in some counties. And Illinois' John R. Block went on to become Ronald Reagan's agriculture secretary.

Well, there's some zaniness in the Brown-Hightower race in Texas, with one trying to out-"good old boy" the other, but it goes beyond that. Hightower thinks that state agriculture departments ought to be serious arms of government, watching out for consumers as well as farmers, and that Texas is as good a place as any to start.

He and Brown are staging a blistering, name-calling campaign that draws a laugh a minute. Hightower says he would get the department into the food pricing issue, help farmers market products and protect their land from development, foster more competition by helping set up cooperatives, carry the farmers' fight to Washington--none of which Brown has done, he charges.

Brown's response to these ideas is to dismiss Hightower as "this turkey who's one of the biggest jokes in Texas . . . . He's never been on a farm, never been in the Texas Agriculture Department. I feel sorry for the young man. He got in the wrong race."

Between them, Hightower (not related to Rep. Jack Hightower D-Tex. ) and Brown expect to spend close to $1 million before the May primary. Hightower, 38, a former U.S. Senate staff aide, author and editor of the Texas Observer, got national political attention in 1980. Running as a self-described populist, he came within a hair of getting elected to the powerful Texas Railroad Commission, which regulates the oil and gas industry.

After a tour as an aide to then Sen. Ralph Yarborough (D-Tex.), Hightower headed the Agribusiness Accountability Project, a farm research outfit in Washington. Among his credits are two books, "Eat Your Heart Out" and "Hard Tomatoes, Hard Times."

His philosophy on agriculture and the energy industry is interchangeable. "I'm a populist and I believe we're being s----ed by the big boys," he says. "I want to do something about it and this office has the power to do something--a fleet of cars and planes, large staff, a daily radio show, field offices. It provides a forum."

Such accouterments helped John C. White hold the office more than two decades. He went on to become chairman of the Democratic National Committee during the Jimmy Carter years.

The railroad commission race whetted Hightower's political appetite and he decided to go after Brown. He has campaigned at full tilt since October, accusing Brown of standing by while agribusiness rolls over the family farmer. "The agriculture commissioner has a record uglier than my face," he says. Hightower's slogan: "No More Bull." His nickname: "Whole Hog."

Brown, 60, a widely known raconteur and long-time official with Texas A&M extension services, claims to be the most accomplished political practitioner in the state, even though his only electoral victory was in 1978 when he won his current job. "The papers down here call me legendary," Brown says. "I'm pretty well-known . . . made over 7,000 speeches in my career."

Brown claims the support of major agricultural groups, but his term has been marked by several run-ins with farmers. One involved near fisticuffs at the Democratic convention last year after a farmer cursed him for supporting Carter.

"We're going to beat this guy like a drum," Brown says. "He's never been a success in anything he did. Both his books look like a freshman thesis. 'Eat Your Heart Out' is a condemnation of everything that's made the free enterprise system great. We'll sink this guy like the Titanic."

Actually, Brown says, Hightower's bound to sink himself. Liberally paraphrasing, he adds, "Thomas Jefferson said if you have to have an adversary, get the b-----d to write a book . . . . Well, no, Jefferson didn't say it exactly that way, but that's what he meant."

"If I can't beat Jim Hightower in Texas, we'd better move to Canada."