The law would subject psychologists, psychiatrists and other mental health professionals to discipline by their licensing boards for providing minors therapy to change their sexual orientation. The state and many professional groups say the therapy is ineffective and potentially dangerous.

A three-judge panel of the U.S. 9th Circuit Court of Appeals agreed to block the law, scheduled to take effect Jan. 1, pending a decision on its constitutionality.

"This is a very good sign for our clients," said Mathew Staver, found of Liberty Counsel, a religious liberties group that sued to block the law, arguing that it violates free speech rights. "To get an injunction pending appeal is a very difficult thing to do."

A spokeswoman for state Atty. Gen. Kamala D. Harris said she would "vigorously defend" a law that banned what she termed an "unsound and harmful practice."

A District Court judge initially rejected the suit by Liberty Counsel, whose clients include a 15-year-old boy undergoing the therapy. The Christian-oriented legal group appealed that decision to the 9th Circuit.

The judges who are hearing the case are Alfred T. Goodwin, appointed by President Nixon; Edward Leavy, a President Reagan appointee; and Milan D. Smith Jr., named to the court by President George W. Bush.

Staver, calling the preliminary injunction "very welcome news," said it was "never routine" and granted only in extraordinary situations when the court believes an appeal has a "likelihood of success."