LYNCHBURG -- He was most noticeable in his absence.

Eight flags fluttering at half-staff and a lone #71 football jersey marked Liberty University's first commencement Saturday without its founder.

Former House Speaker Newt Gingrich urged the graduating class to honor the Rev. Jerry Falwell's spirit by confronting "the growing culture of radical secularism" with Christian principles.

Gingrich, who is weighing a 2008 presidential bid, continues a trend of using Liberty's commencement as voice box for conservative politicians. Last year, Republican John McCain gave the address at the religious school started in 1971 by Falwell, a Baptist preacher who later founded the Moral Majority that helped catapult Ronald Reagan into the presidency in 1980.

Falwell's two sons made their first appearance since the elder preacher's death Tuesday. Jerry Jr., chancellor of the university, and Jonathan, executive pastor at Thomas Road Baptist Church, flanked Gingrich on the podium before a crowd of 17,000 seated in the university's football stadium.

Before commencement, in a small room overlooking the colorful scene of excited graduates, Jerry Falwell Jr. said showing up was a way to honor their father.

"I'm going to be really upbeat because that's what Dad would have wanted," said Falwell Jr. "I've cried more this week than at any other time in all of my 44 years."

Later, he addressed the university for the first time as its chancellor.

"No one can replace Dad, but ...," said Falwell Jr. haltingly as he was overcome with emotion. Spontaneously, people clapped as he struggled for composure. "But there's a team here ready to carry on, and we're going to give it everything we have as he did for so long."

Saturday's class was the largest so far at Liberty, with 3,598 undergraduates, graduate students and distance learners. The university, with about 120,000 alumni, has grown to three campuses. An engineering school is scheduled to start in the fall, and a medical school is planned to open in five years, Falwell Jr. said.

This year's graduates included the first 50 students from the university's inaugural law school class.

Gingrich's 30-minute speech included readings of Bible passages and from Franklin Roosevelt's D-Day radio address. He encouraged students to end "this anti-religious" bias and inject God in the public square.

"A growing culture of radical secularism declares that the nation cannot profess the truths on which it was founded," Gingrich said. "We are told that our public schools can no longer invoke the creator, nor proclaim the natural law nor profess the God-given quality of human rights."

Surveying the packed stadium, Gingrich told the graduates that they were Falwell's legacy. Saturday was the second time he was chosen as commencement speaker. He was conferred with an honorary doctorate of humane letters.

He said Falwell told him a man's worth isn't measured by his talent or wealth but by what it takes to discourage him. He said the university's founder persevered in his faith.

"If you seek a monument to that perseverance, look around you," he said. "Look around this stadium, across this campus and in this city."

The day was bittersweet for some, as exhilaration blended with sorrow. Prayers and songs were peppered throughout the ceremony. Silly string lassoed professors. Mortarboards were decorated with crosses and with words, including "Jerry's Kid 4 Life."

Paul Tomlinson, 22, wept after he watched a montage of pictures of Falwell's life, including black-and-white photographs on his wedding day and a photo of him holding a Donald Duck soda bottle from the abandoned plant where he started his church.

"It's such a sad day," he said. "I know Jerry's smiling down on us. It's like he graduated ahead of us."

Ruth Santino of Gettysburg, Pa., sat on the grassy slope as she watched her daughter graduate. "I think this is a very joyous affair, and yet honors Dr. Falwell at the same time."

Becky Falwell, Jerry Jr.'s wife, said the graduation was "absolutely beautiful." She began tearing up as she anticipated the June 2 graduation of her son, Trey, 17, -- the first grandchild -- from Liberty Christian Academy. "His grandfather won't be there to see him. And four years from now it'll happen again" at the university.

Ray Simms, 69, one of the 35 members of Falwell's original church started in 1956, quietly watched the graduation unfold. He said he had to come.

"I used to go to youth rallies with Jerry before he was a pastor," Simms said. "It's been a rough week. I just felt I had to be here."