About 150 people gathered Thursday in the Mission District to discuss an idea that some say is crazy even for San Francisco: opening a city-funded, legal center where intravenous drug users can congregate, get free needles and inject themselves in a safe environment.

Momentum for such a center seems to be gaining strength among drug reform advocates and some public health workers, who say it will help stop the spread of HIV and hepatitis C, prevent deaths from drug overdoses and keep dirty needles off city streets.

Advocates for the center, who call themselves Alliance for Saving Lives, sponsored the event along with the city's Public Health Department.

They are gathering signatures on a letter to send to Mayor Gavin Newsom, the Board of Supervisors and Dr. Mitch Katz, head of the Public Health Department.

Supporters include the San Francisco AIDS Foundation, the Mission Neighborhood Resource Center, the Harm Reduction Coalition and San Francisco General Hospital's Opiate Treatment Outpatient Program.

The letter reads in part, "We call on San Francisco to create a legal Safer Injection Facility staffed with trained medical professionals. ... Please help us make this critical program a reality."

But so far, no San Francisco politician appears ready to champion the cause. Newsom, meeting Thursday with The Chronicle editorial board, said he doubts any neighborhood in the city would be willing to play host to hundreds of intravenous drug users on a daily basis.

The obvious choice for the center - the Tenderloin, where many of the users live - already deals with more than its share of social service providers while also being home to many families and children, Newsom said.

"You put another center in there, you're going to enhance and advance some conflicts that are already there," he said. "I'm not ideologically against it - I'm just pragmatically concerned."

The hesitation doesn't surprise those who work in British Columbia at Insite in Vancouver's Downtown Eastside, which is akin to San Francisco's Tenderloin in that it is an impoverished neighborhood with many drug users. Insite, which opened four years ago, is North America's only injection drug center, though many exist in Europe.

It took 10 years of community organizing for the Vancouver center to go from idea to reality, said Sarah Evans, the center's program coordinator, who spoke Thursday at the San Francisco symposium.

Insite is a rather bland, sterile place used by 800 intravenous drug users every day. They bring their own drugs - most often heroin, crack, cocaine and crystal methamphetamine - but are given free needles by the center's staff. The center hands out and collects 2 million needles a year.

The center has three rules: no violence, no dealing and no injecting anybody but yourself. Eight staff, including nurses and counselors, are at the center at any given time. It recently opened an on-site residential detox and recovery program.

Despite a lot of initial skepticism, the Vancouver center now has the backing of the majority of the public, the mayor, the police chief and local merchants, Evans said.

"The evidence is really clear that we're achieving our goals for the users and the community," Evans said. "The more you look into it, the more you realize it's crazy not to do it."

The center has proven it can help stop the spread of disease and prevent deaths from overdoses, said Dr. Thomas Kerr, an HIV/AIDS researcher at the University of British Columbia. He has studied Vancouver's injection facility since its inception, and spoke at Thursday's event.

Kerr said 800 overdoses have happened at the facility, but they have resulted in no deaths because trained professionals are right there. Without the center, overdoses would happen in back alleys or single-room-occupancy hotel rooms where there would be no help, he and other supporters of the facility said.

"It's really been studied to death - it's time to move on," Kerr said. "It's obvious this is something that works."