The contest to represent San Francisco’s quiet District Four — the Sunset — has turned into one of this year’s loudest races, as the front-runners, Jessica Ho and Gordon Mar, spar over neighborhood ties, campaign contributions and comments in the Chinese-language press.

Entire storefronts on Irving Street, one of the busiest commercial arteries in the neighborhood, have been shrouded in campaign posters, while both Ho and Mar have pilloried each other in mailers and TV ads.

And the two campaigns for a seat on the Board of Supervisors aren’t the only sources of ammunition: Outside donors have spent more than $600,000 on Ho’s behalf, while labor unions have spent more than $90,000 supporting Mar.

But in the backdrop is a relaxed, family-oriented neighborhood that usually isn’t the stage for knockdown, drag-out political fights.

“We don’t like the way that the race has become,” said Christian Kropff, Ho’s campaign manager.

“We wish it wasn’t like this,” said Mar’s campaign manager, Edward Wright.

For several years, the District Four seat has been held by a political appointee. Current Supervisor Katy Tang was widely expected to win if she ran for re-election. But her surprise decision not to enter the race and instead endorse Ho, her new legislative aide, left the race open.

While there are six other candidates in the race, Mar and Ho — considered the front-runners because of their endorsements and the money they have raised — have focused on attacking each other.

Ho, 30, a Los Angeles native who was an intern for former District Four Supervisor Carmen Chu and student at UCSF, moved to San Francisco in March to work for Tang, who was appointed to the seat when Chu became assessor-recorder in 2013. Mar, 56, is a longtime community and labor activist in the Sunset.

Their latest spat centered on a scathing press release from Ho’s campaign that accused Mar of telling the Chinese-language newspaper, Sing Tao Daily, that he opposes Proposition 10 — which would overturn California’s rent-control restrictions — while telling English-language audiences that he supports it.

Mar denied the accusation and said the paper mischaracterized his comments. He shot back by accusing Ho of misrepresenting how long she has actually lived in the Sunset. Another dispute was about Mar accusing Ho of changing her position on local Proposition C, which would tax large businesses for funds to spend on homeless services. And, most recently, a paid staff member of Mar’s campaign was caught tearing down a Ho campaign poster.

At the same time, voters are getting inundated with biting campaign flyers, like one paid for by an independent expenditure committee supporting Mar that highlights a post on Ho’s Facebook page, a picture of Los Angeles with the caption, “Home is where the heart is.”

“She was talking about LOS ANGELES not SAN FRANCISCO,” the mailer reads.

Meanwhile, public school teacher Trevor McNeil, the most notable candidate after Mar and Ho, has largely stayed above the fray. McNeil, who has raised far less money than Mar and Ho and hasn’t benefited from any third-party spending, said the negativity between Mar and Ho has put a cloud over the race.

“It has been disappointing to see people going negative,” McNeil said. “Especially in a district that hasn’t had a contested election since 2006, people are really interested in the issues. ... I feel very confident of our strategy of staying positive, because I think ultimately it’s going to pay off.”

Given the different political leanings of Mar and Ho, it makes sense that the District Four race has spiraled into a tense battle, said longtime political consultant Jim Ross.

Ho is considered a moderate, who would largely carry on Tang’s agenda. Mar has a progressive track record and would likely tilt the Board of Supervisors toward the left on issues such as homelessness and housing.

“I think it is the one race that could change the dynamic of the board,” said Ross, who isn’t involved in any local campaigns this election. “It could lead to who is going to be the next board president. If Ho wins, it will likely be someone more moderate. If Mar wins, it would likely be someone more progressive.”

While they both oppose a Navigation Center and support building more housing in District Four, their biggest differences can be spelled out in their positions on Prop. 10 and local Proposition C, which would tax large businesses for funds to spend on homeless services. Ho opposes both measures, while Mar supports them.

Mayor London Breed endorsed both Ho and McNeil, who is also considered a pro-housing moderate.

“I know that both Jessica and Trevor will work with me to support families and working people in our neighborhoods,” Breed said in a statement. “It’s important that we elect people who put neighborhoods before politics.”

The amount of outside spending funneled into the District Four race indicates how much outside interests — from real estate investors to labor unions — feel is at stake, likely because of issues around housing and development in the neighborhood. But no independent committee has spent nearly as much on any supervisor campaign as the $618,789 Progress San Francisco, a SuperPAC that often backs moderate candidates in local races, has spent supporting Ho.

And Mar’s campaign, which has received $93,194 from independent expenditure committees — such as the San Francisco Labor Council Labor & Neighbor Independent Expenditure Political Action Committee — hasn’t missed a chance to accuse Ho for being bought by third-party interests.

Meanwhile, some voters said they couldn’t care less about all the drama.

“What it comes down to is, what are they trying to do?” District Four resident Nate Wiley said outside Java Beach Cafe across from Ocean Beach on a recent, fogless afternoon in the Sunset. “Just because they have been here for a long time, doesn’t mean they have a certain set of values.”

Trisha Thadani is a San Francisco Chronicle staff writer. Email: tthadani@sfchronicle.com Twitter: @TrishaThadani