The veteran filmmakers both made brief remarks and were joined by university officials, alumni and hundreds of supporters at the celebration, which also featured a performance by the USC Trojan Marching Band.
"We're now officially a legitimate school . . . at least we look like one," joked Lucas, one of the school's most famous alumni, and creator of the "Star Wars" franchise.
Lucas -- whose Lucasfilm Foundation provided $75 million for the new facilities, plus $100 million for the school's endowment -- took a small group of journalists and photographers on a tour of the school's two new structures, the George Lucas and Steven Spielberg buildings.
The completed facilities have a combined 137,000 square feet of space, and are home to 10 classrooms, 19 conference rooms, eight screening rooms, six editorial labs, three mixing rooms, nine sound editorial rooms, a foley stage and three picture editorial rooms.
"When I went to school here, we had a large steel desk with a big knob on it," Lucas recalled, while observing two film students at work in the mixing room. "Times have changed. It's much better. Now it's all digital."
More construction is under way. By 2010, the Animation and Digital Arts building and three production buildings, which will house four sound stages as well as production services, are scheduled to open.
"Because of George's dedication to the school, we're in the position where we can offer the finest level of instruction," said Douglas Wellman, the school's director of facilities and operations. "And he's been very hands-on. He's approved everything down to the doorknobs."
Even though studios including Warner Bros., 20th Century Fox and Disney have also donated money to the school, $50 million still needs to be raised.
"The whole idea is to teach people how to make film," Lucas said. "The people who come out of here are high quality . . . they deserve high-quality facilities."
Still, the famous filmmaker whose first big box office success came with 1973's "American Graffiti," missed certain elements of his students days at USC. "It was sort of fun in the old, funky days," Lucas said. "You're of your time. I liked the fact that we were rebels."
Every year since 1973, at least one USC alum has been nominated for an Academy Award, Spielberg told the crowd gathered in a Spanish-style courtyard.
Spielberg, perhaps the world's most famous director, was rejected from USC's film school as a young man but was awarded an honorary degree in 1994 and became a trustee in 1996. "Since 1980, I've been trying to be associated with this school," joked the 62-year-old filmmaker. "I eventually had to buy my way in."