SAN FRANCISCO (Reuters) - A group opposed to male circumcision said on Tuesday they have collected more than enough signatures to qualify a proposal to ban the practice in San Francisco as a ballot measure for November elections.

But legal experts said that even if it were approved by a majority of the city's voters, such a measure would almost certainly face a legal challenge as an unconstitutional infringement on freedom of religion.

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.

The leading proponent of a ban, Lloyd Schofield, 59, acknowledged circumcision is widely socially accepted but he said it should still be outlawed.

"It's excruciatingly painful and permanently damaging surgery that's forced on men when they're at their weakest and most vulnerable," he told Reuters.

His group submitted about 12,000 signatures supporting his proposed ban, said Rachel Gosiengfiao, campaign services manager for the city's Department of Elections. The agency has 30 days to verify the petitions. He needs 7,200 valid signatures to qualify.