With pressure mounting to deal with San Francisco’s swelling tent encampments, Mayor Ed Lee is moving to turn a Mission District warehouse into a “pop-up” 120-bed homeless shelter.

“The goal is to try and ramp up and get as many people off the streets as possible,” said Public Works Director Mohammed Nuru, who is helping in the shelter setup and whose aggressive cleanups of tent camps have drawn the wrath of advocates for homeless people.

The Mission shelter would be in a warehouse at 1515 S. Van Ness Ave., and be open for seven or eight months starting in early June. The center is expected to cost about $2.5 million and be open around the clock, with some counseling and support services on site.

It would be a scaled-down version of the city’s two Navigation Centers, which have larger staffs to help homeless people find jobs and deal with issues such as substance abuse and mental problems. Like the Navigation Centers, the goal at the Mission shelter would be to get at least some homeless people into permanent housing.

Since the start of the year, outreach workers have managed to “transition” four large homeless camps — each with 40 or more residents — into Navigation Centers and other shelters, along with five smaller camps.

There are plenty more: Sam Dodge of the Department of Homelessness and Supportive Housing estimates there are 19 camps in the city with at least six people. Public Works puts the number of camps at 37 — though its definition of a camp is one where at least two people are living.

The planned Mission Center would be limited to campers in the Mission, where homeless-aid officials estimate that 150 people are living on the streets.

At first, plans called for making the South Van Ness shelter a full-scale Navigation Center. But officials feared it would take too long to get one of those up and running, given the burgeoning camp problem in the neighborhood.

“The mayor is moving aggressively because he realizes there is an issue with the encampments in the Mission,” said Lee spokeswoman Deirdre Hussey, “and he is working closely with (district) Supervisor Hillary Ronen.”

Ronen, who took office in January, told us Tuesday that “the tent encampment crisis in the Mission is completely out of control. In my view, it’s a public health crisis.”

The South Van Ness site became available when Ronen brokered a deal with developer Lennar Multifamily Communities for an apartment project. Lennar is letting the warehouse be used as a shelter until the firm breaks ground next year.

The shelter will give Lee political cover for Public Works’ camp cleanups by providing a place where displaced residents can go.

Those cleanups have become a source of friction at City Hall. Department of Homelessness and Supportive Housing officials have complained that the Public Works sweeps are undermining their efforts to build trust among those living in the camps and get them off the streets. But Public Works says the camps — where workers have found rats and thousands of used needles — have become a public health hazard.

Bad night: A retired Los Angeles police detective hired by San Francisco District Attorney George Gascón for his new unit probing police officer-involved shootings was arrested on suspicion of public drunkenness last week while attending a training session for D.A. investigators near Sacramento, authorities say.

The trouble started for Roger Guzman when he and another man were picked up by an Uber driver outside a Roseville bar at 2:14 a.m. Thursday, according to police in the Placer County city.

After driving the two men about a mile and a half, the driver stopped and ordered both of them out.

“They were creating a disturbance, so (the driver) kicked them out of his car and called us,” said Roseville police spokeswoman Dee Dee Gunther.

Both men were arrested for allegedly being drunk in public and were taken to the county jail in Auburn to dry out.

Inebriates arrested in such cases typically are released without charges after several hours once they’ve sobered up, Gunther said. That appears to be what happened in this case. A spokeswoman for the Placer County D.A.’s office said no charges were filed against either man.

San Francisco Hall of Justice sources say Guzman, who earns $116,000 a year, was attending a two-week training course mandated for D.A. investigators by the state Commission on Peace Officers Standards and Training when he was arrested.

The district attorney’s office said it couldn’t comment on Guzman’s arrest because it was a personnel matter. “However, the D.A. takes these matters very seriously,” said spokesman Alex Bastian.

Guzman did not return our calls seeking comment.

He was hired as part of the city’s move to make the district attorney’s office the primary investigator in police-involved shootings, supplanting Police Department inspectors.

Just last week, Gascón said his office would not file charges against two police officers who killed a knife-wielding man, Amilcar Perez-Lopez, in the Mission District more than two years ago. It was the first ruling that Gascón has made in a fatal police shooting in nearly 26 months, and leaves his department still dealing with a backlog of 10 fatal shootings by police in San Francisco.

San Francisco Chronicle columnists Phillip Matier and Andrew Ross appear Sundays, Mondays and Wednesdays. Matier can be seen on the KPIX TV morning and evening news. He can also be heard on KCBS radio at 7:50 a.m. and 5:50 p.m. Monday through Friday. Got a tip? Call (415) 777-8815, or email matierandross@sfchronicle.com Twitter: @matierandross