Everyone has heard all the excuses that San Francisco supervisors have for keeping homeless Navigation Centers out of their districts — too hard to find the right site, costs too much, not enough need in their neighborhoods.

But those excuses would no longer be tolerated under a proposal by District Six Supervisor Matt Haney. The legislation Haney plans to introduce at next week’s board meeting would force each district that doesn’t already have a Navigation Center to open one in the next 30 months — no matter what.

“It is critical that we step up and say we are going to all be part of the solution,” Haney said. “This is not just talk. This is action. This is commitment.”

The city’s eight Navigation Centers are clustered in Districts Six, Nine and 10, which include neighborhoods with large homeless populations like SoMa, the Mission and the Bayview. Haney’s legislation would sprinkle eight more centers around the city, even in districts that are well-to-do and have smaller homeless populations. But the ordinance outlines no formal punishment if a district does not build a qualified facility in 30 months.

District Nine Supervisor Hillary Ronen, District 10 Supervisor Shamann Walton and District Four Supervisor Gordon Mar are co-sponsoring the legislation. Haney said he hopes more of his colleagues will sign on by Tuesday.

Navigation Centers provide intensive health and housing services and have more lenient rules than traditional shelters. Other facilities that would qualify under the legislation include sites that offer services to people living in cars and RVs and those focused on homeless transgender youth.

Haney’s plan comes as a proposed 200-bed Navigation Center on the Embarcadero in his district is facing intense pushback from neighbors. Neighbors say the facility, proposed by Mayor London Breed, would attract more homelessness and crime to the area.

But legislation forcing all districts to open their own sites, Haney said, would help supervisors show constituents that building a shelter in their neighborhoods is a civic responsibility.

“The supervisor can say this is part of a citywide plan, it’s something we’ve all committed to and it’s going to make a difference in addressing homelessness in our city,” he said. “It’s important to have something ... that demonstrates shared responsibility.”

Some board members said Thursday that they support the concept of Haney’s legislation, but are dubious about how realistic it is, given how difficult and expensive Navigation Centers are to build.

Several supervisors without Navigation Centers in their districts said they have already been trying to find spaces, but have had no such luck.

“Space in some of the districts is really limited,” said District Five Supervisor Vallie Brown, who has been looking for a place to put a Navigation Center, or other type of shelter, in the Haight. “I think every district should have a Navigation Center, but the problem is just trying to find space for one.”

Navigation Centers are often temporary structures built on land slated for development. But finding open land that is both big enough and has access to utilities is difficult.

They are also expensive. Building a Navigation Center from scratch, or renovating an existing building, can cost the city $2 million to $3 million. That high price tag can quickly become hard to justify when the site is just temporary.

Haney did not have a specific funding proposal, but said he would help identify funds for these new Navigation Centers in the next few budget cycles. Breed already plans to allocate money in the next two budget cycles to fulfill her promise of creating 1,000 more shelter beds by the end of 2020.

District Two Supervisor Catherine Stefani, who represents neighborhoods with low homeless populations, such as Pacific Heights and the Marina, said she is open to a Navigation Center in her district — but added they should go in areas where they will have the most impact.

“The placement of Navigation Centers should not be a politically driven choice,” Stefani said.

District Eight Supervisor Rafael Mandelman, who also has been looking for sites, said forcing the city to build a center in every district may not be the “magic formula” to solving San Francisco’s homeless crisis. He is worried that locating Navigation Centers in areas where they may not be viable could slow down the city’s ability to build more shelter space.

“I want to get shelter beds up and running as quickly as possible,” he said. “If (the legislation) gets us closer to that goal, then I’m inclined to support it. If it moves us away from that, then I’m inclined to oppose it.”

Meanwhile, Breed’s office has also been looking for sites all around the city. In the past few months, her office has vetted and rejected more than 100 locations, ranging from a shuttered Pottery Barn in the Castro to the empty 6x6 mall on Market Street.

“All neighborhoods need to be part of addressing our homeless and housing crisis,” said Jeff Cretan, the mayor’s spokesman. But “we have to balance our need for Navigation Centers to be built across the city with the need to create opportunities quickly to help people who are unsheltered today.”

The legislation — called “Navigating Homelessness Together” — also says that the city must have at least three community meetings and coordinate with the district supervisor when a site is proposed. It also says the department must create criteria for how sites are chosen, such as size and proximity to public transportation.

Haney said “this is the beginning of the process with this legislation” and he expects to amend it with his colleagues.

Most supervisors did not take a firm position on the legislation Thursday as they had yet to see the official language. But the fact that many are already looking for sites is a departure from a few years ago, when the late Mayor Ed Lee received a lukewarm response when he asked each supervisor to identify sites in their districts.

Mar, who represents the Sunset, said his district should play a role in helping the city’s homeless population, even though the neighborhood has historically bristled at the idea of a homeless shelter.

Though Mar initially didn’t think there was much need in his district for a Navigation Center, he has since changed his position, as the area’s homeless population has grown.

“I believe that citywide problems like homelessness require citywide solutions,” Mar said. “But similar to the debate around increasing housing density in all districts, I believe that it’s important to work with the community to come up with the most appropriate way to do that.”

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