"It's a waste of city resources, and it's a ruination of people's lives for doing knuckleheaded stuff," said Councilman James Kenney, the bill's sponsor. "Everyone has done knuckleheaded stuff, but we don't get locked up for it, we don't have a criminal record that follows us for the rest of our lives."
It's unclear how quickly the law may take effect. It could be months.
Mayor Nutter said Thursday that he would carefully consider the bill before deciding whether to veto or sign it. A veto would send the bill back to Council for another vote.
Councilman Dennis O'Brien argued against the ordinance, saying it would be trumped by state law, which makes it illegal to have any amount of marijuana. The measure is ripe for a legal challenge, and experts have told him it could easily be overturned by the state Supreme Court.
"State law preempts City Council action," he said after the hearing.
Even if the measure becomes law, police will still have the discretion to make an arrest and place charges. And other police departments in the city, such as housing and campus officers, still would have the authority to make arrests.
"It's going to be confusing," O'Brien said.
On Thursday, though, Philadelphia stood with those communities that have decided that arresting people for a little pot is not worth the expense or the trouble.
"It puts Philadelphia clearly on a contemporary curve," said Allen St. Pierre, executive director of NORML, a national nonprofit lobbying group that works to legalize marijuana. "It's a good trend, one that's clearly happening around the U.S."
Part of the shift, said St. Pierre, is due to the change in attitudes among those running local governments today.
Fifty years ago, when the World War II generation was in charge, marijuana was seen as an evil, destructive drug. Now, baby boomers who often have had first- or secondhand experience with pot are serving as mayors and council members. They're more likely to question why their governments spend money to arrest pot-smokers when schools are hurting and roads are falling apart.
Twenty-one states and the District of Columbia have laws that legalize some form of marijuana use, according to Governing magazine, which studies data on laws and operations. Only Colorado and Washington state have legalized marijuana for recreational use, while the others allow pot for medical reasons.
New Jersey permits medical-marijuana use. Pennsylvania, Florida, New York, and Ohio have legislation or ballot measures pending to legalize marijuana for patients.
The Philadelphia bill says nonviolent drug and alcohol abuse is a health issue, not a criminal matter. Arresting people for small amounts of pot does nothing to deter drug abuse, "but does increase the number of people with life-changing criminal records," the bill states.
Anyone found with less than 30 grams, equal to 1.06 ounces, could be ticketed and fined, not arrested.
The bill noted that Chicago began letting police issue tickets instead of making arrests in 2012, and Washington, D.C., passed a similar ordinance this year. Philadelphia, the bill said, has "a critical need" to deploy law enforcement personnel toward violent offenses.
Efforts to reach Police Commissioner Charles H. Ramsey were unsuccessful.
James Engler, Kenney's director of legislation, said the bill would go immediately to Nutter.
If the mayor vetoes the measure, it returns to Council, which would act at its next scheduled session, Sept. 11. The same 13 votes would be enough to override the veto, Engler said, and make the measure law.
Kenney is pushing to have the bill take immediate effect, planning to deliver a letter to the mayor on Friday that urges him to make a fast decision.
"Our fear is that he's going to wait and then make a decision in September," Engler said. By then, scores of young people will have been arrested, he said.
This isn't the first time Philadelphia officials have tried to lessen pot-possession penalties.
In 2010, Seth Williams, then the new district attorney, implemented a policy to all but decriminalize possession of small amounts for personal use - part of an effort to unclog Philadelphia's crowded courts.
The idea was for prosecutors to charge those cases as summary offenses rather than misdemeanors. People arrested with up to 30 grams would pay a fine, but face no risk of a criminal record.
But even as the District Attorney's Office stopped prosecuting most minor possession cases, police continued to arrest smokers, often locking them up overnight to await arraignment. Prosecutors would refer nearly all those cases to the Small Amounts of Marijuana program, where defendants' records could be expunged in exchange for a $200 fine and attendance at a drug class.
In Philadelphia, the number of people arrested for marijuana possession was roughly the same last year as the year before, 4,336 in 2013 compared with 4,272 in 2012. Last year, 13 percent of those arrested were younger than 18.
On Thursday, 24-year-old Tashira Moss told Council she got arrested last month for having $5 worth of marijuana.
Now, while looking for a job, she's worried her prospects could be hurt by an arrest record.
"I'm in a whirlwind of craziness right now," she said. "Now I don't know who is going to hire me."
Bishop J. Darrell Robinson of Yesha Ministries testified that he has worked with black youths for three decades, and that minor pot arrests are ruining their lives.
"Their future is jeopardized, their ability to make money in the city and lead a decent life is jeopardized, because of a small amount of weed," he said. "I'm here in support of this bill."
He decried what he called "racially biased" policing.
In recent years, both the ACLU and the NAACP have focused on the racial disparities involved, the black leadership group saying African Americans were nearly four times more likely than whites to be arrested on pot charges.
Kenney, speaking after the Council hearing, reiterated that black youths were disproportionately arrested - and that locking up small-time offenders was a waste of police resources and city funds.
"It's almost impossible for a young person to get a job these days," he said. "With a record, it's totally impossible."
Inquirer staff writer
Dylan Purcell contributed
to this article.