Supervisor Scott Wiener will announce he is running for state Senate Wednesday, setting the stage for an election still 1½ years away, but already generating intense speculation about what progressive candidate will run against him.

A moderate Democrat who is one of the most prolific but divisive members of the Board of Supervisors, Wiener has championed increased funding for transportation, an expansion of the police force and — notoriously — a ban on public nudity. He has endorsements from state Attorney General Kamala Harris, Lt. Gov. Gavin Newsom, state Sen. Mark Leno — whose seat Wiener seeks to occupy — and Board of Supervisors President London Breed.

Even with such endorsements, Wiener is sure to face a tough race. The question is against who.

The most likely candidates are Supervisor Jane Kim and former Assemblyman Tom Ammiano. Democrat Kim is a former Green Party member who has championed affordable housing and comes from the ranks of the Asian political establishment.

Ammiano is the standard-bearer of the city’s left, and has the benefit of widespread name recognition. In 1999, he famously mounted a write-in campaign for mayor that forced incumbent Willie Brown into a runoff.

Campos may run

Another potential candidate is Supervisor David Campos, who lost a race for Assembly last year to fellow Supervisor David Chiu by a razor-thin margin. Campos had made a name for himself taking on Airbnb and advocating on behalf of the Mission District, including his controversial bid to temporarily halt the construction of market-rate condominiums in the neighborhood.

The prevailing opinion is that if Ammiano decides to run, Kim and Campos won’t.

Ammiano the favorite

Ammiano is the “800-pound gorilla,” Campos said. “If he decides to run, he will be the odds-on favorite to win that seat. If he doesn’t, we’ll see. A lot of us want him to run.” As for whether Campos would run, he said he likes being in San Francisco right now. “But it’s politics. You never say never. So I never rule anything out.”

In a text message, Ammiano said he would decide soon, and noted that polls are strong in his favor and that people he has contacted in Sacramento are enthusiastic about him running. He said if he doesn’t seek the seat, he would support a “candidate that reflects my political perspective and has a proven record” and “not just lip service.”

Ammiano, who was a political mentor to Campos, did not respond to a question about whether he would support Kim.

Also in a text message, Kim said, “Nothing is off the table. I’m definitely interested in the work and impacts that can be made on the state level. Right now, my focus is on District 6.”

A race between two supervisors — all of whom work in close quarters with offices on the same floor — could lead the board to take up more wedge issues that would highlight the supervisors’ differences. To the extent there has been disputes, such as on expanding the police force and the proposed building moratorium in the Mission, Wiener frequently clashes with Kim and Campos.

Political consultants are keeping tabs.

“There is a little bit of a parlor game going on in San Francisco right now,” said political consultant Eric Jaye. No matter who the progressive camp puts forward, he said, “it will be a tight race.”

The gay vote

To the degree the gay community will coalesce behind Wiener will likely depend on who runs against him, as both Ammiano and Campos are also gay. Political consultant Jim Stearns, who has advised many progressive candidates, said Wiener has “divided the gay community” with his policies. “One of your strengths as an LGBT candidate is unified gay support, and he does not have that.”

Who would have a better shot at beating Wiener depends on whom you talk to.

Jaye said Kim would be the more formidable candidate.

“Jane Kim would have the benefit of the progressive voters, the lion’s share of the Asian community, and a strong story to tell to moderate Democratic women beyond the progressive base,” he said. “While Ammiano would poll well at the beginning because of his name recognition, he has also historically been quite polarizing. He is well-liked by some, and much less well-liked by others.”

But Stearns said Ammiano has the clear edge.

“If Tom runs, Tom wins,” Stearns said. “He is really well-known, well-regarded, and has the experience of being in the state Assembly and would be able to garner statewide labor support. The major institutions like the Sierra Club, the teachers, the nurses would get behind him.”

Jumps into race

Wiener isn’t waiting to see who his opponent will be. And he has his own list of unions supporting his candidacy.

They include the San Francisco Police Officers Association, United Food and Commercial Workers Western States Council and the International Brotherhood of Electrical Workers, Local 6.

In an interview, Wiener said he is most proud of his record championing funding for transportation, changing regulations to allow for more in-law units, and requiring new buildings to create infrastructure to use gray water to conserve water.

Opposed moratorium

He also led opposition to Campos’ failed moratorium on building market-rate condominiums in the Mission and opposed an initiative to use transit funds to give free Muni passes to low-income youth, saying the money should go to vehicle and equipment maintenance. Google later stepped in to fund the program.

“People can agree or disagree with me on different issues but they'll never have to guess what my view is,” Wiener said. “I think it's very important to have principles and be very clear about them.”

Emily Green is a San Francisco Chronicle reporter. E-mail: egreen@sfchronicle.com Twitter: @emilytgreen