WASHINGTON >> In an institution hampered by perpetual uncertainty, there are a few comforting givens on Capitol Hill.

Bean soup is always on the Senate cafeteria menu. Reporters stand unceasingly idle behind a string of red velvet ropes, waiting to shove a recorder in the face of a senator departing the floor.

And Rep. Tim Johnson, R-Ill., perpetually paces the Capitol hallways, a cellphone pressed to his ear as he talks to constituents, whom he calls all day long, one by one, just to say hello.

He calls them as he walks to go vote, plowing through the Longworth House Office Building, then traversing the Capitol Rotunda and zooming beyond his colleagues, a phone pressed tightly to his right ear as if it grew there.

He calls them as he wanders through his district’s shopping malls and the parks near the Capitol, his staff chasing alongside with large binders, a mobile virtual office.

He calls them from the treadmill at the members’ gym.

“I can remember several occasions in the House gym where we started out on treadmills or exercise bikes at the same time, and both got in pretty healthy workouts,” said Rep. Ron Paul of Texas. “There was one big difference: As we worked out next to each other, I read the paper and watched the news. Tim had a call list he dialed through and talked to dozens of constituents.”

He calls them so often that most of his colleagues have never seen him without a cellphone, except when he canters to the House floor to vote.

Johnson — a willowy figure, so kept by the combination of constant motion and a diet consisting largely of hot tea and granola — will soon be a Capitol Hill fixture no more. Elected in 2000, Johnson abruptly announced after winning his primary that he would retire at the end of the year, citing, among other things, a “grossly gerrymandered congressional map” in which “two-thirds of the voters have never been represented by me.”

No one likes to contend with new constituents — Rep. Barney Frank of Massachusetts said redistricting was one of his motivations to retire — but Johnson, 65, was not simply nervous about appealing to new voters. He was worried about a whole new set of first phone dates.

Johnson, a thrice-divorced father of nine, calls roughly 4,000 of his 700,000 constituents each year.

“I am almost like a dinosaur,” said Johnson, who would agree to be interviewed only by, yes, phone. “I think people think I am unique,” he added, clearly embracing the notion of understatement. “My style makes you sufficiently out of the mainstream and people can wonder how effective you are.”

He cuts a slightly disheveled swath through the Capitol at all hours, his calling often cited by colleagues as his chief accomplishment after a decade of service here.

“Tim had his finger on the pulse of his district,” Speaker John A. Boehner said in an email, “and always reminded members that at the heart of every democracy are representatives who will listen first, learn, and then lead.”

Johnson said his calling habits grew out of his many years in the Illinois Legislature.

“I came to the conclusion that the problem with government is that they were too out of touch with people and had very little individual relationships,” he said.

His political passions were inherited from his parents, he said, “kind of the way some families are farmers.” His father’s family were Southern Democrats involved with the Truman campaign, and his mother came from “strong Republicans from Central Illinois.”

Johnson, a lifelong Republican, first served on the City Council in Urbana, Ill. He has one of the most independent records in the House, with a roughly 50 percent positive rating on his votes from liberal and conservative groups alike. Republican House leaders never quite know which way Johnson will go on any number of matters — he was against them on a payroll tax holiday and opposed a troop presence inB Afghanistan.

Johnson has attributes that most people do not see, said Rep. Daniel Lipinski, a moderate Democrat from Johnson’s home state.

“I always appreciated how he literally marches to the beat of his own drummer,” Lipinski said, recalling his colleague’s passionate questioning of witnesses as a guest in a 2008 Science and Technology Committee hearing that always stuck with him, and his very occasional floor speeches, like one opposing a Republican tort reform bill.

“He rarely speaks on the floor, but when he would speak, he was really, really good,” he said. “I think most members never really saw it.”

Johnson said he is happy to be known as the caller, mostly because his constituents so appreciate hearing from him and asking him to address their problems.

“No one person stands out more than another,” he said. “In most cases they were happy, in a few cases tearful, I guess at the thought that a congressman would talk to an individual from a small town in Central Illinois. And in a few cases it’s angry about my votes. Hopefully it has been beneficial to the system.”

For now, he is hanging up.

“The truth is, it’s missed baseball games, missed weddings and a couple specific situations that arose very recently with my family,” he said, explaining his desire to return to private life at the end of the year, hoping he left his impression along the marbled halls. “I want people to remember that I was a voice of common sense and real people living in the real world.”

© 2012 The New York Times Company