In a battle of incumbents, the eccentric prevailed over the outsider yesterday as Rep. Andrew Jacobs Jr. defeated Rep. David W. Evans in Indiana's Democratic primary for Congress from Indiana's 10th Congressional District, which includes Indianapolis.

The two, forced to run against one another by a Republican-penned redistricting plan, found few ideological difference over which to to spar, and instead spent their time arguing about who had done a more effective job representing his constituents.

Jacobs, an eight-term incumbent who has built a record as a penny-pinching progressive, won heavily in the black sections of the inner-city district as he piled up an overall margin of 5 to 3 over Evans.

With all precincts reporting, Jacobs had 24,934 votes to Evans' 14,148.

In another Indiana Democratic primary yesterday, Rep. Floyd J. Fithian defeated state Sen. Michael Kendall for the right to square off against Republican Sen. Richard G. Lugar in the fall.

Fithian had 59 percent of the votes with 61 percent of the ballots counted, rolling up 165,880 votes to Kendall's 116,878.

Lugar, a popular former mayor of Indianapolis, ran unopposed for renomination to a second Senate term, but his television advertising budget made it plain that he is not taking the fall campaign lightly. He has spent $250,000 on TV, and reportedly is amassing a $3 million war chest for his reelection campaign.

Fithian, a former college professor who saw his 2nd Congressional District in northwest Indiana wiped out by redistricting, had planned to run for Indiana secretary of state, but switched to the Senate race at the last moment, when he sensed that Indiana's unemployment rate of more than 13 percent might make Lugar vulnerable.

Fithian's primary against Kendall developed into a bit of a grudge match. Fithian originally prevailed on Kendall to get into the race, then pulled the rug from under his younger opponent's campaign by getting into it himself.

Republicans control Indiana's legislature, the governor's office and both U.S. Senate seats. Last year they put together a redistricting plan intended to turn what is now a 6-5 Democratic edge in the congressional delegation into a 5-5 split or a 6-4 GOP advantage. The state is losing one congressional seat to reapportionment.

The chief victim of the reapportionment was Evans, a tireless campaigner and constituent service specialist who tried to overcome Jacobs' local party backing and longer term of service by knocking on 30,000 doors in seven months.

It did not work. Jacobs, regarded as one of the wittiest and most offbeat members of Congress, won more easily than had been expected.

In his 15 years in Congress, Jacobs, 50, has distinguished himself for not accepting pay raises, turning down all political action committee contributions and trying to shame colleagues on the Ways and Means Committee whenever they vote with the special interests.

"I have a reputation for hearing the clash of a different cymbal, if not the beat of a different drummer," Jacobs has said of himself.

During the campaign he avoided personal attacks on Evans, and concentrated instead on criticizing Reagan's economic program. "The economy is so bad," he told voters, "that even people who don't intend to pay aren't buying."

The new district Jacobs has been nominated to represent is heavily Democratic and about one-fourth black. He is expected to have an easy ride in the fall.

Most other congressional incumbents won easily amid light turnouts yesterday, but some may face difficulty in the fall.

Democrats Adam Benjamin Jr. and Lee H. Hamilton were unopposed in their primaries, and Rep. Philip R. Sharp defeated nominal opposition. Sharp is expected to have his hands full in a district where Republicans have increased their share of registered voters.

On the GOP side, incumbents John Patrick Hiler, Dan R. Coats, Elwood Hillis, John T. Myers and Joel Deckard all won without opposition.