SAN FRANCISCO, July 28 (Reuters) - A California judge ordered a proposal to ban circumcisions of boys in San Francisco removed on Thursday from an upcoming municipal ballot, saying it would infringe on religious freedom.

But Superior Court Judge Loretta Giorgi, in finalizing a tentative decision reached on Wednesday, said she technically barred the measure on grounds that state laws disallow voter initiatives governing medical practices.

The law "leaves no room for localities to legislate in this area," the judge wrote in her formal opinion.

Circumcision is a ritual obligation for infant Jewish boys, and is also a common rite among Muslims, who account for the largest share of circumcised men worldwide. But critics of the practice argue that it amounts to genital mutilation.

The measure, which would have applied only to San Francisco, sought to make it a misdemeanor crime to perform a circumcision on a boy before his 18th birthday, regardless of the parents' religious beliefs. The maximum penalty would be a year in jail and a $1,000 fine.

According to attorneys present at a hearing on Thursday, Giorgi warned that even if the proposed ban were reduced in scope to exempt medical professionals, it would still run afoul of First Amendment protections for religious expression.

"Judge Giorgi couldn't have been clearer," said Abby Porth, associate director of the Jewish Community Relations Council in San Francisco. "You can't sever healing arts physicians from rabbis."

A dozen petitioners sued to block the initiative, which was added to the ballot after proponents gathered more than 12,000 signatures in San Francisco. A similar effort in Santa Monica, a coastal city west of Los Angeles, was withdrawn.

San Francisco resident Lloyd Schoefield, a proponent of banning circumcision named in the suit as a real party in interest, had sought to allow the ballot initiative go forward as an exemption to state laws under an escape clause for health or safety considerations.

In a telephone interview on Thursday, Schoefield criticized the judge for not allowing a debate in court over the health or safety of circumcision.

"We are discussing our next course of action but not gearing up for an immediate appeal," Schoefield said. "We don't have the legal power that our opponents do."

The move to outlaw circumcision in San Francisco raised alarm bells for Jewish groups across the nation.

In June, the Anti-Defamation League condemned a comic book created by supporters of the anti-circumcision movement that it said contained grotesque anti-Semitic imagery. The comic featured a character named "Monster Mohel" as an evil villain.

A mohel is a Jewish individual specifically trained to perform the ritual circumcision of infant boys.

(Reporting by Emmett Berg)