About 50 people attended the "Come Out of Homosexuality" event, where the Reverend Jerry Falwell spoke by video-conference, reports CBS station KPIX-TV.
Activists accused Falwell of promoting violence such as the beating death of gay Wyoming college student Matthew Shepard.
"Christian bigots out of our city!" cried Josh Trenter, who was hauled away by police after allegedly tossing a blueberry pie. Michael Johnston of the Kerusso Ministries, a Falwell supporter, told CBS Radio Station KCBS-AM he was hit in the side of the head by the pie. Another report said it hit only the video screen on which Falwell was speaking.
Trenter and another member of a gay rights group were cited for battery and released.
Declaring that "God loves you and so do I,'' Falwell said that "just as people can come out of the closet, so can people choose to come out against a sinful lifestyle.''
The presentation was designed "to reach out to the homosexual community in a spirit of love,'' said Allen Wildmon, a spokesman for the American Family Association, a conservative Christian group that sponsored the event with Falwell, the former leader of the now-defunct Moral Majority.
"This is not to force anybody's views on anyone,'' said Wildmon, who timed the lecture to counter publicity from National Coming Out Day, an annual event celebrating gay life. "We all have a freedom of choice in America.''
The event came as jury selection began in the first-degree murder trial of Aaron McKinney, accused of killing Shepard in Laramie, Wyoming. Falwell condemned Shepard's killers and said the lecture's timing was coincidental.
The timing "was very tacky,'' said San Francisco Supervisor Tom Ammiano, who has long been active in the gay rights movement. "I think it's extremely disrespectful and I think it reflects the depth of their insensitivity and self-serving agenda.''
Fellow Supervisor Leslie Katz agreed.
"There's such hatred that comes out in that approach. It implies people can change,'' Katz said. "That's the behavior that results in people on the fringes committing grievous acts against others.''