Six o'clock on a Wednesday evening, and in the barren storefront that passes for the Kennedy headquarters here, Virginia Hood is trying to translate names on a stack of index cards into commitments from local citizens to vote for her candidate at the Jan. 21 precinct caucuses.

She started out in politics stuffing envelopes for Adlai E. Stevenson more than two decades ago. In 1960 she worked for John F. Kennedy, and in 1968 backed the insurgent effort of Eugene McCarthy. She went to the 1972 Democratic convention pledged to George McGovern. Four years ago she helped Birch Bayh carry surrounding Woodbury County in the caucuses that sprung Jimmy Carter from the obscurity of the pack.

She is at best bemused by the attention her state is now getting. "It's not a new program for us," she says. "We go through this every two years."

Cal Olson has been around town only a couple of years. He says Sioux City has a "quintessential grass-roots smell," something he tries to pay attention to as editor of The Sioux City Journal.

Local interest in the upcoming caucuses? "I don't hear it," Olson says. "I don't hear much preparation noises."

At a time when the elite of America's political industry and a small army of journalists are descending on this friendly state, the comments of Hood and Olson suggest that while the invaders may be agog over the caucuses, the natives aren't.

That doesn't make the outcome of those caucuses any less important to the political fortunes of President Carter, Sen. Edward M. Kennedy (D-Mass.) or the flock of Republicans traipsing around here. But the people of Sioux City know the candidates have more to win or lose by the outcome than does the town.

Sioux City snuggles against a bend in the Missouri River near the conjunction of Iowa, Nebraska and South Dakota. An early supply center for explorers heading into the northern plains, it was settled in the 1850s by Germans, French Canadians and Scandinavians.

The first railroad arrived in 1868, and with it came the meatpacking industry. In the boom times of the 1880s, Sioux City's population leaped fivefold from 7,366 to 37,086. The city's growth was stunted during the depression of the 1890s but resumed in the early 1900s.

By 1920 there were more than 70,000 people here, including a sizable community of Russian Jews, and the stockyards and packing industry had come to dominate the local economy.

"It was the best business town in the Midwest in those days," says Harry Smith, Sioux City's leading labor lawyer.

Today it no longer is, "This town has had a tough 10 years," Olson says.

Like other cities, Sioux City has suffered from changes in the structure of the national economy. New ways of fattening, slaughtering and transporting livestock diminished the city's role as a packing center. One by one, the major packers moved out to open smaller, more specialized plants closer to farmers and feedlots.

The only major packer left, Iowa Beef Processors Inc., has given the town, in addition to several thousand jobs, three long, bitter and occasionally bloody strikes in the last 10 years. Today the company is counted as a plus by the city fathers, but its difficulties in the last decade have underscored the falling fortunes of a one-industry town.

Sioux City attracted other industries over the years. The leading light was a Zenith television plant. A little less than two years ago, Zenith closed up, blaming competition from the Japanese.

"The psychology of that was terrible," Olson says. "People here started to get paranoid."

Over the decade, Sioux City lost 14,000 industrial jobs, according to Cornelius J. (Conny) Bodine, a former city manager, now a consultant.

But people here think things have turned around. The gasohol craze has attracted some North Carolina investors who plan to open what purportedly would be the nation's biggest alcohol plant, relying on the corn that is so abundant around here for raw material. The fellows who run the stockyards say the place is making a comeback. And just before Christmas, General lMotors said it would take over the old Zenith plant and produce carburetors for the next generation of GM cars.

The GM announcement has done more to make Sioux Citians feel good about themselves than all the attention being lavished on them by the presidential candidates and the national media.

For a few people around here, the precinct caucuses offer more opportunity for advancement than the new GM plant. These are the young lieutenants fighting the trench warfare of caucus organizing.

Mark Farnen, 22, speaks with the candor of the young. He grew up in Missouri in a political family, learned about political organizing by passing out literature at ice cream socials in his hometown, and became addicted forever when at 15 he was a last-minute volunteer substitute for an absent politician at a local oratory contest.

He's now the Carter-Mondale coordinator in the Sioux City area. Instead of a storefront, he works out of an apartment.

"Kennedy's pulling out all the stops. He's really spending money, Farnen says, "I think Carter's more popular among the people, but these Kennedy folks, well, I think I'm out-organized here."

Rich Norman, 24, arrived in Sioux City in early December, a veteran of more than half a dozen political campaigns in his native Virginia. He is looking forward to two things this month: helping George Bush finish first or second in the caucuses and leaving town.

He knows Sioux City mostly through a pile of computer printouts indentifying potential Bush voters. For the first two weeks he saw little more than his hotel room, his office and a few local restaurants.

He sees Bush as strong on the wealthier north side of town and Reagan in good shape on the less wealthy southeast side. John B. Connally, Norman says, is a poor third everywhere.

His payoff for a good Bush showing is a better assignment is a later primary state, and with enough experience his own political consulting firm.

By the time Sioux City Republicans begin to gather for the caucuses on Jan. 21, his bags will be packed and in the trunk of his car. By Jan. 22, Sioux City will be for him just another campaign ribbon.

None of this is lost on the people here. They may participate in the caucuses, but they don't expect immediate fulfillment.

Marilyn Murphy considers herself a Democrat, a liberal and an activist. She expects to take part in the caucuses on Jan. 21. But so far, none of the candidates has addressed an issue that presses heavily on Sioux City and the surrounding region. That is the future of the family farm.

Murphy is a member of the Coalition to Preserve the Family Farm, an offshoot of the Catholic Diocese of northwest Iowa, and she helped conduct studies that have shown a dramatic increase in farming by people who don't own the land. She fears that the trend could fundamentally alter life in the region over the next decade, and for the worse. So far, she says, none of the candidates has raised the issue, much less said what could be done to reverse the drift toward absentee ownership of farm land.

"Who's been here to give a farm speech that is something other than a perfunctory set of policies?" she asked.

Tim Heikes, 28, hasn't decided whether he'll go to the caucuses, though he is paying attention to what the candidates are saying. A registered Republican, he has some kind words for Carter, and says, there's too much old blood among the Republicans.

He used to farm with his father, but when the dairy business went bad a few years ago he got out and took a construction job. Today he rents the spread of an older farmer south of Sioux City and wonders if he'll ever be able to buy his own farm. That's what the politicians mean when they talk about accepting a lower standard of living.

"I always try to vote," Heikes says. "But I don't have too much faith in the system." He expects a little short-term gain from the elections, but not much more. "I look forward to better prices because of it," he says. "That's all."

That may be all that Sioux City will get from this caucus enterprise, a quick fix with no lasting side effects one way or the other. For it is the ceaseless rhythms that have carried this place from boom town to stagnant city and on the way back, not the quadrennial cycles of presidential politics, that will leave a permanent mark.