A flood of money from powerful interest groups is pouring into the tight state Senate race between San Francisco Supervisors Scott Wiener and Jane Kim in what has become this year’s showdown between the city’s moderate and progressive camps.

On Wiener’s side: charter school associations, LGBT groups, and technology executives and companies. On Kim’s side: the Service Employees International Union, teachers and nurses associations, and tenants’ rights organizations funded in part by the soda industry.

The state Senate seat is a coveted position in San Francisco’s cramped political universe, where ambitious politicians struggle to grab the few opportunities for higher office. The race also underscores the power struggle between the moderates and the progressives, who have clashed on how to respond to the city’s housing and homeless crises.

Wiener, the moderate, has a more than 2-to-1 financial edge in direct contributions and heavy support from independent expenditure committees. Those committees, which cannot coordinate their efforts with candidates, can raise and spend unlimited amounts of money for political purposes. Technology investor Ron Conway, for example, has pumped $200,000 into an anti-Kim committee.

But if anything, the state Senate race shows just how difficult it can be to trace the source of political money. Major contributions are routinely filtered through two and three committees before the money is finally spent in the form of television ads, slate mailers or robocalls.

“It’s a way for people to hide their identities, and they know it,” said Ann Ravel, former chairwoman of the Fair Political Practices Commission, the state’s campaign finance watchdog. “And so that’s the reason they are taking these very extreme avenues to do what we call the nesting dolls of campaign contributions, so you can never get to the original source.”

Here’s some of what’s gone on in the race for the District 11 seat:

• The largest direct donors to Wiener’s campaign are building trade unions, real estate groups and police unions. Kim’s largest contributors are teachers and nurses groups.

• Wiener has raised more money locally than Kim. As of mid-October, roughly 68 percent of his campaign contributions had come from ZIP codes within District 11, compared with 41 percent for Kim. More out-of-state money is also flowing into Kim’s campaign than Wiener’s. Some of that comes from employees at the New York cosmetics company Kiss, where her father is chief financial officer.

• Independent expenditure committees have spent $1.5 million to support Wiener, more than five times the amount spent for Kim. Of the outside money backing Wiener, the easiest to trace is from Conway. He’s the main money behind the committee We Can’t Trust Jane Kim for Senate, which has spent more than $173,000 on ads attacking Kim for her 2012 vote to reinstate former Sheriff Ross Mirkarimi after his domestic violence scandal.

Both campaigns have condemned their opponents’ various industry connections, but that tells only part of the story. Some of the biggest donors are hidden behind a web of committees.

Take the Equality California Political Action Committee, Wiener’s biggest financial backer and the outside committee spending the most in the race. As of Friday, it had put up $855,000 for canvassing, consulting, advertising and polling to help Wiener, according to state records.

The group’s stated mission is to advocate for “candidates who support full equality for lesbian, gay, bisexual and transgender Californians and allies,” which would include the openly gay Wiener. The money behind Equality California’s political action committee tells a more nuanced story.

Its biggest contributor is the California Charter Schools Association Advocates, which — along with a sister organization, the Parent Teacher Alliance — has given more than $400,000 to the Equality California committee. Most of the Charter Schools Association Advocates’ money comes from a handful of billionaires, including former Los Angeles developer Eli Broad, media baron and former New York Mayor Michael Bloomberg, and Netflix CEO Reed Hastings.

The link between the charter schools and Wiener is not accidental. The Parent Teacher Alliance also has its own independent expenditure committee, which has spent close to $380,000 supporting Wiener.

Richard Garcia, a spokesman for the Charter Schools Association Advocates, said the group believes “Mr. Wiener has the greater ability to effect positive growth for students in San Francisco and not be a proponent of status quo agendas.”

Equality California’s other top contributors are the California Dental PAC, the California Apartment Association and the California Association of Realtors — each gave more than $170,000.

The Realtors’ interest in the race reflects the political divide on the Board of Supervisors: Kim believes developers can and should rent a quarter of all new units at below-market prices. Wiener wants the city to do a study before committing to a percentage. He is more supportive of market-rate development to build up housing stock and bring down prices.

Rick Zbur, executive director of Equality California, said his group sought donations after making it clear that its priority is getting Wiener elected. Roughly 80 percent of the committee’s political contributions during this election cycle have gone toward this race.

“We cast a broad net, and whoever is willing to support our effort we accept,” Zbur said.

Wiener, meanwhile, has criticized Kim for ties to the American Beverage Association. The trade group has spent nearly $19 million to defeat a ballot measure that would impose a penny-per-ounce tax on soda and other sugary drinks in San Francisco.

While most of the American Beverage Association’s money has gone toward television ads slamming the measure as a grocery tax, some of its money is winding its way to down-ballot races — much of it to Kim’s benefit. Kim’s political consultant, Eric Jaye, also advises the American Beverage Association.

Through a committee known as No on V, Enough is Enough: Don’t Tax Our Groceries, the American Beverage Association has contributed $250,000 to the Affordable Housing Alliance and the San Francisco Tenants Union. Those groups in turn have spent that money on slate mailers, which urge a no vote on Proposition V — and prominently feature Kim as a champion of affordable housing.

Deepa Varma, executive director of the San Francisco Tenants Union, said: “We dislike Big Soda, but we dislike regressive taxes more.” That’s also Kim’s position and the reason she is opposed to Prop. V’s soda tax. Varma said her group decides what candidates and ballot measures to support or oppose, and then “those campaigns and candidates send us money in order for us to produce mail or slate cards.”

The soda group has no interest in who wins the state Senate race, Jaye said, noting that the association has also given $32,500 to committees that put out slate mailers backing Wiener.

While Kim’s campaign argues that the financial filings show that Wiener is beholden to special interests, that’s not the way Wiener’s team sees it.

“Both sides are benefiting from donations from tech, real estate development and other business interests,” said Maggie Muir, a consultant for Wiener.

Joaquin Palomino and Emily Green are San Francisco Chronicle staff writers. Email: jpalomino@sfchronicle.com, egreen@sfchronicle.com Twitter: @JoaquinPalomino, @emilytgreen