Washington ? The fifth floor of the Longworth House Office Building has the feel of a college dorm the week before registration. The smell of paint is in the air, the halls are choked with boxes, desks are in piles. Spools of telephone wire are everywhere. And over there, in Suite 1504, the bookshelves are empty and the carpet is a mess.

In a week’s time the three rooms in this decidedly junior suite — no shimmery view of the Capitol from here — will be the headquarters of Rep. William J. Janklow, Republican of South Dakota. Just a few days earlier he was Gov. Janklow, and he commanded the best office in the Statehouse in Pierre. But, then again, just a few days ago an entire state leaned to hear his every whisper. Beginning next week, Janklow, one of the mouths that roared in American politics, will speak in a whisper that almost no one will heed.

He’s going to be a freshman congressman, a form of life that makes him Washington’s equivalent of a paramecium: He’s alive, of course, but he’s not likely to attract much attention or make many waves. He has a vote, to be sure, and a staff. But it won’t be like the old days, when the Legislature actually had to listen to what he said and when the newspaper reporters strained to be sure they got his quotes right. If he’s quoted this year, it’ll be because some weekly paper reprinted his press release.

One of his South Dakota predecessors, Rep. Francis H. Case, was memorably described by Lyndon B. Johnson aide Harry McPherson as “pale, square, and deadly dull.” Janklow is none of those things.

His fate as a governor-turned-House member, an extremely rare phenomenon, came to Janklow by choice, not as a form of punishment. Most of the movement between the House back benches and the governor’s chair goes the other way, with an ambitious lawmaker seeing an opening to be a chief executive of a state — and, instantly, a presidential contender. (Number of governors elected president since 1880: 8. Number of House members elected president since James A. Garfield: None.) But Janklow, who served as governor for 16 years, wasn’t permitted by law to succeed himself, and since he isn’t the retiring type, the House was about his only option.

He’s in for a surprise, and not only because he’s been assigned a top-floor office that gives him one of the longest commutes between his desk and the floor. He’s moving from an executive job to a legislative job, from a role as soloist to a member of an ensemble. But one of the things that is changing, too, is the scale. Rep. Michael N. Castle, a sixth-term Republican who served two terms as governor of Delaware, already has told Janklow that his actions now affect more than 280 million people. The population of South Dakota is well under a million, and its largest city, Sioux Falls, has about 120,000 souls.

Janklow’s not talking about his new challenge, or the new scale of things, but some of those who went before him warn that the adjustment is going to be difficult.

“As governor, you’re on the direct firing line,” says Castle, whose state, like South Dakota, has only a single member in the House. “In the House you are one of more than 400 members. It is a major cultural shift. It makes you change your outlook.”

Former Sen. Dale Bumpers of Arkansas, who came to Washington after serving as governor in Little Rock, says the adjustment is jarring — and discomfiting. “When you’re governor, you proclaim an order or have an education plan and something happens,” he says. “Here you have to jump through a lot of hoops before anything happens. When I first came here I can’t describe to you the frustration I felt. It’s a dramatic and radical change.”

This dramatic: Back in Arkansas he sometimes got his proposals passed in two days. Here in Washington he was lucky to prevail in two years. Mostly he didn’t.

Janklow, an activist governor who has luxuriated in lowering taxes and submitting a budget actually lower than the year before, isn’t a bystander by temperament. He is known as Wild Bill; he was once seen charging around the state house with a shotgun. He’s innovative; he put state prison inmates to work at building housing for the elderly. He’s iconoclastic; eight years ago he told me: “I don’t respect the political insiders. I just don’t. They’re insincere. Everything’s reduced to a calculation where you don’t tick off anybody. I tick off a lot of people but I don’t care.”

He is going to want to jump in, to speak his mind, to make an impact. He may, of course. But Rep. Castle advanced in the House by becoming the classic inside guy. He belongs to three coalitions. He tends to home-state corporate issues by sitting on the Financial Services Committee. He’s done the quiet, hard work required to help shape education policy. “As a former governor, you have a really good sense of how these programs work,” says Castle. “A lot of House members don’t.”

Not that Janklow, 63 years old, doesn’t know what is coming. The biography on his Web site sets it out: “He has often said that being governor for the great people of South Dakota is the best job, the most challenging job, and the most enjoyable job that anyone could ever have.”

But that’s not his job now. His job now is coming to peace with the slower life of the House. For a man known to be intolerant of idiocy, life in Washington is going to be tough for Bill Janklow.

David Shribman is a columnist for The Boston Globe.