WASHINGTON, D.C. — A senior White House aide predicted this week that President Obama will use his authority under the Antiquities Act to designate more new national monuments — and big monuments — before he leaves office. If Congress will not act to preserve America’s scenic and cultural treasures, the President “has his pen and intends to use it,” John Podesta, a counselor to the President, told a dinner marking the 50th anniversary of the landmark Wilderness Act.