Photo: Liz Moughon / The Chronicle

San Francisco Mayor London Breed’s plans to add 280 new beds for the homeless has two supervisors worried she is prioritizing the quantity of beds over the quality of care.

Supervisors Hillary Ronen and Matt Haney say the mayor’s expansion plans in their districts — 60 beds to the Division Circle Navigation Center, 20 beds to Civic Center Navigation Center and building a new, 200-bed center on the Embarcadero in South Beach — doesn’t seem to include a corresponding increase in services and security. This has put them on edge about adding new beds in their districts, which already host the majority of the city’s homeless services.

In particular, Ronen said adding too many beds to the Division Circle Navigation Center could “erode the model that we spent years creating.”

“This could lead to worse outcomes for both the unhoused residents of the Navigation Center as well as their surrounding neighbors,” Ronen said in a recent letter to Jeff Kositsky, director of the Department of Homelessness and Supportive Housing, regarding the Division Circle expansion.

Meanwhile, Haney said he is “not convinced” that a proposed 200-bed Navigation Center on Seawall Lot 330, which would be the biggest in the city, will offer the same level and quality of services as a traditionally smaller shelter. The number of beds at other centers around the city ranges from about 60 to 130.

“Adding 100 more people to a Navigation Center is not something we have seen yet, and that hasn’t been proven successful yet,” he said. “We’ve got a lot of questions about how to get this right.”

But Jeff Cretan, a spokesman for the mayor, said the larger centers will offer a similar level and quality of services as existing facilities. Funding for the expansion, which comes from the city’s recent $415 million windfall, include both capital and operational costs for increased on-site staffing.

Photo: Scott Strazzante / The Chronicle

Breed, who is steadily chipping away at her promise to add 1,000 beds — in both standard shelters and Navigation Centers — by 2020, originally proposed a plan to fund the extra beds for four years through the windfall. But the supervisors, including Ronen and Haney, voted to slash that funding to two years to make room for other priorities such as increased teacher salaries and energy independence.

Navigation Centers are temporary structures that have more relaxed rules than traditional shelters, offer robust services to steer people into permanent housing and allow round-the-clock stays. But since they are expensive to build and operate for just a few years at a time, the mayor’s office is pushing a new model called the SAFE Navigation Center, which offers similar services as Navigation Centers — but will be bigger and exist longer.

If the Port of San Francisco allows the city to use the land, the 200-bed shelter on the Embarcadero will be the city’s first SAFE Navigation Center.

The timely opening of the shelter relies heavily on two ordinances sponsored by the mayor, which would exempt shelters and Navigation Centers from the building permit process and expedite the hiring of contractors to manage the facilities. The Board of Supervisors will vote on both pieces of legislation Tuesday.

Even though the mayor’s office said there would be a corresponding increase in services at the proposed center, Haney said he is still apprehensive to support a model that has yet to be tested in the city.

“The big shelter warehouse model is not one that we seek to replicate in our city, and that’s why we’ve pursued the Navigation Center model,” he said. “And it’s important that we stick to those principles.”

Residents of Rincon Hill, South Beach, South Park and Mission Bay jammed two community meetings last week in overwhelming opposition to the Embarcadero Navigation Center. Meanwhile, Ronen said she has received concerns from her constituents about the Division Circle expansion.

Their comments also come a few weeks after a number of supervisors blasted the Department of Homelessness for the bureaucracy and logistics involved in creating more Navigation Centers. Ronen particularly criticized the department, saying there is a lack of specifics on when and where the city would provide more shelter beds. She also said that her colleagues need to step up and welcome more services to their districts, too.

In her letter to the department, Ronen asked for assurance that the expansion would also come with increased neighborhood security and a promise that the homeless will not be asked to leave the center until “suitable housing is obtained.”

“I just want assurance,” Ronen said, of her letter to the department. “I never agreed to the weakening of the very carefully crafted model that we know works.”

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