SACRAMENTO — Officials in San Francisco, San Diego and Los Angeles counties will be able to expand conservatorship rules to give them more control over who can be involuntarily held for mental-health treatment.

Gov. Jerry Brown signed SB1045 by Sen. Scott Wiener, D-San Francisco, on Thursday. The bill creates a five-year pilot program in the three counties intended to get more mentally ill people who suffer from substance abuse off the streets and into treatment.

The bill was among 350 that were still on Brown’s desk before Thursday. Sunday is the deadline for the governor to act on bills.

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Wiener said SB1045 will give the three counties the tools they need to help mentally ill people. Brown signed the bill without comment.

San Francisco Mayor London Breed and Supervisor Rafael Mandelman told lawmakers in June that current conservatorship laws often block counties from helping people suffering from both mental illness and substance abuse if they refuse assistance.

“It’s neither progressive nor humane to watch as people deteriorate and die on our streets,” Wiener said in a statement Thursday. “We have a moral responsibility to help people get healthy and thrive.”

County mental health professionals can now hospitalize people against their will for 72 hours, in what is known as a 5150 hold, if they pose a danger to themselves or others or are gravely disabled because of mental illness. A county can ask a judge for a 14-day extension to continue intensive treatment and repeat that process every 30 days.

Under SB1045, boards of supervisors in San Franisco and the other two counties will be able to vote to expand when a person can be involuntarily held. People with frequent 5150 holds could be placed under a conservatorship for a year, during which they would be provided with housing and treatment.

Opponents of bill, including Western Center on Law and Poverty and American Civil Liberties Union, said expanding involuntary holds would strip people of their civil rights and ignore the factors that lead them to be homelessness in the first place.

Brown also signed SB1017 by State Sen. Ben Allen, D-Redondo Beach (Los Angeles County), which will phase out fishing gear that is responsible for the unintentional deaths of dozens of marine mammals every year.

The bill targets drift gill nets, long nets used to catch swordfish. They can unintentionally trap and kill dolphins, seals, and the occasional endangered sperm whale and leatherback sea turtle.

Among the bills remaining on Brown’s desk:

•SB822 by Sen. Scott Wiener, D-San Francisco, which would create the strongest net neutrality protections in the country. The regulations would bar internet service companies from slowing rival websites or those that don’t pay for faster service.

The bill has faced intense opposition from the telecommunications industry, which argued that it is a federal issue and that state-by-state regulations are impractical.

•SB905 by Wiener, which would allow San Francisco, Oakland and seven other California cities to keep their bars open until 4 a.m., two hours later than the current mandatory closing time.

•SB320 by Sen. Connie Leyva, D-Chino (San Bernardino County), to require health centers at University of California and California State University campuses to offer abortion pills. That bill would take effect in 2022.

•SB1437 by Sen. Nancy Skinner, D-Berkeley, which would change the state’s felony murder rule that holds an accomplice in an offense such as robbery liable for a homicide that happens during the crime, regardless of whether the defendant was involved in the killing.

Melody Gutierrez is a San Francisco Chronicle staff writer. Email: mgutierrez@sfchronicle.com. Twitter: @MelodyGutierrez