President Bush encountered widespread protests yesterday when he received an honorary degree and spoke at the commencement of his alma mater, Yale University. Graduating students heckled Bush, held up signs that read “Conservation, Not Consumption” and “Don’t Turn Your Back on the Environment,” and handed out “Got Arsenic?” stickers. Some students from the Yale School of Forestry and Environmental Studies wore miniature power plants on their mortarboards and burned incense through the smokestacks. More than 170 Yale professors boycotted the ceremony, claiming Bush was not worthy of the degree. Bush lost the presidential race on the campus last fall, 49 percentage points behind Al Gore and 2 points behind Ralph Nader.