Where most people have knuckles, Rep. David W. Evans (D-Ind.) has calluses.

They are forget-me-nots of a punishing, incumbent-versus-incumbent Democratic primary campaign, arranged courtesy of the Republican-controlled state legislature.

In settlement of some old accounts, the GOP thoughtfully gerrymandered Evans out of his district and tossed him into a fight for survival against Rep. Andrew Jacobs Jr., who happens to be the only other Democrat who's managed to prosper politically in this most Republican of the nation's big cities.

Their primary, which winds up this Tuesday, has nothing to do with interest rates, Social Security benefits, defense spending, or any other issues of the hour, on which the two have staked out middle-of-the-road records. The question is more fundamental: How should a congressman go about being a congressman?

Evans, in eight years in Congress, and Jacobs, in 16, have fashioned dramatically different answers, and their fratricidal fight is a triumph of stylistic differences over substantive ones.

Evans, 35, an earnest, intense former parochial-school social studies teacher, is the congressman-cum-caseworker. He peppers his constituents with mail, town meetings and home visits; thinks nothing of knocking on 30,000 doors in a campaign; and sees the highest calling of his office as helping a voter track down a Veterans Administration benefit form or a wayward Social Security check.

Jacobs, 50, a tall, angular vegetarian, is the congressman-cum-gadfly. His chief weapon on the House Ways and Means Committee has been the power of shame. When the committee voted a tax break for the Gallo winery, he showed his disapproval by buying a gallon of Gallo and pouring his colleagues some thank you cups.

Jacobs declines congressional pay raises ("Somebody's got the organ grinder and the monkey mixed up," he says); gives back most of the money allocated to his office for staff expenses; uses his franking privilege only to respond to constituent mail; and refuses political action committee contributions, on the theory that "the only reason they aren't bribes is that Congress gets to define bribery."

As to whether these self-denials are wholly principled or partly tactical, former Marion County Democratic chairman William Schreiber, says: "I've known him for 20 years and I've never been sure. But I'll say this: they've been worth a couple of million dollars of publicity."

The differences between Evans and Jacobs are partly generational, but they concern personality and necessity as well.

The district Evans has been serving since his come-from-nowhere Watergate upset of 1974 is heavily Republican. He has responded by assuming the posture of a round-the-clock candidate, and never more so than this year.

The newly fashioned 10th District he is running in is heavily Democratic, covering all of inner-city Indianapolis. Jacobs represents 52 percent of it, Evans just 40 percent. Moreover, at one time or another, Jacobs has represented all of it.

"If everybody holds his own, we win," says James Beatty, a Jacobs adviser.

No one understands that math better than Evans, who has been burning shoeleather like a man posessed since last fall. He has knocked on 30,000 doors since Oct. 1, devoting roughly 35 hours a week to the task. He's taken time off only when the wind chill dived below minus 20, or to make a rare trip to Washington, where he's checked in an average of just a day a week this year.

Even with all that, Evans has found it necessary to run--literally. "We started out walking and we found we just weren't covering enough houses," he says matter-of-factly.

Evans makes his rounds with two aides, one who stays a house ahead of him and finds out if anyone is home, and another who follows in a car and keeps updating a master computer voter list.

"Code her E and pro-life," Evans will shout to the driver as he darts from house to house, meaning that the voter he has just visited should receive campaign mail especially targeted to Evans voters who are opposed to abortion.

Evans' own staff is sometimes distressed by the hours he devotes to his "walks," as they are misnamed. "We've tried to get him to be a little more legislative, but it's hard," said one aide.

Jacobs, too, says he baffled by the frenzied pace of his opponent.

He takes a far more conventional approach, going door-to-door by telephone only, talking before local ward organizations (who have given him their endorsement) and appearing on three live, half-hour "Ask Andy" television call-in shows, where his ready wit shows to good advanatge.

Neither man publicly attacks the other, and on the surface at least, it is the most civil of campaigns. But the usual campaign tensions are there.

"When have you ever seen a congressman before?" they like to ask voters when they campaign in Jacobs' section of the new district.

Jacobs' supporters fire back that Evans has politicized the perks of his office. They claim that it costs at least $25,000 to send a franked mailing to all constituents and that Evans uses the process as a kind of polling service, feeding the responses to his questionnaires into his political operation.

All this, of course, is standard operating procedure for most congressman, and Evans makes no apologies. Ditto for his acceptance of PAC money.

Their voting records are similar, but not identical. Jacobs made a name for himself in the late 1960s as a pro-Great Society, antiwar activist. Since then, his votes have veered toward the middle, with his inbred fiscal convervatism coming more and more to the fore. One profiler has called him a "parsimonious progressive." Evans, too, follows the socially liberal, fiscally conservative path.

One key battleground between the two will be the city's black community, which accounts for 25 percent of the new 10th District and as much as 33 percent of the vote in a Democratic primary. Jacobs, who has represented more of the black community longer, is thought to have an edge.

While the Evans-Jacobs race is the most hotly contested primary in the state, it is not the only one affected by the the GOP redistricting plan.

Rep. Floyd Fithian (D-Ind.) saw his northwest district wiped out and decided to run for the Senate. Fithian is running against an energetic but little-known state senator, Michael Kendall. The winner will face Sen. Richard G. Lugar, whose aura of invincibility has recently been pierced by the state's 13 percent unemployment rate.

Four-term Rep. Philip R. Sharp, a Democrat from Muncie, has found his new district more Republican, and there is a three-way GOP pirmary under way for the right to take him on.

The other two Democrats in the state delegation, Rep. Adam Benjamin Jr. and Lee H. Hamilton, survived redistricting in good shape. Neither faces primary oppostion, and both are thought to be safe in the fall.