The NPS has a great year by year history of the lighting of the National Christmas tree. President Carter actually didn't light the full tree - in honor of the Iranian hostages:
On December 13, the President had his daughter light the National Christmas Tree, but to everyone’s surprise, the switch only illuminated the star-shaped tree topper and the blue lights that lit-up the state trees on the Pathway of Peace. In President Carter’s Christmas greeting, he announced that the National Christmas Tree would remain dark until the American hostages were set free. He said, “Amy had lit fifty trees – one for each American hostage. We will turn on the rest of the lights when the hostages come home.” The President then requested a moment of silent prayer.