WASHINGTON — A 17-year-old transgender youth, Leelah Alcorn, stunned her friends and a vast Internet audience in December when she threw herself in front of a tractor-trailer after writing in an online suicide note that religious therapists had tried to convert her back to being a boy. In response, President Obama this week will call for an end to such psychiatric therapies aimed at “repairing” gay, lesbian and transgender youth, White House officials said. His decision on the sensitive issue is the latest example of his continuing embrace of gay rights. In a statement to be posted on Wednesday evening...