AUSTIN, Texas (Reuters) - The Lance Armstrong Foundation said on Friday that donations rose sharply as fans of the cancer nonprofit pledged support, but the organization faces long-term questions about its future now that its cycling champion founder was stripped of a record seven Tour de France titles.

At the foundation's light-filled headquarters in the Texas capital, where Armstrong lives, a receptionist took a call from a well-wisher, a scene that Chief Executive Doug Ulman said was repeated throughout the day in an outpouring of calls, emails and social media messages, many from cancer survivors touched by the foundation's work.

"It's people offering to help in any way they can, people committing to additional donations, people saying, âI'm going to go buy a Livestrong shirt to show my support,'" Ulman said. "So the mood is actually pretty positive."

Armstrong was stripped of his Tour titles and handed a lifetime ban by theUnited States Anti-Doping Agency after he said on Thursday that he would not challenge USADA's charges that he had doped throughout his career. He continued to deny that he ever used performance-enhancing drugs.

Ulman said the supporters of the foundation "respect Lance's decision and I think they just want to move on."

The 100-employee foundation said it received 400 donations totaling $75,000 on Friday, an increase of 20 times from the amount donated the day before. Ulman said the organization, which raised $51 million in 2011, "is incredibly sound financially."

But the fact that the foundation bears Armstrong's name puts the organization in a tough spot, said John Daly, a professor of communication at theUniversity of Texas at Austin.

"It's like calling it the Enron Foundation - there's a challenge there," Daly said, referring to the energy company that filed for bankruptcy in 2001. "People who have given to it or know what it does probably won't be bothered. But it's going to be hard to write a donation letter right now."

In two other recent cases, charitable foundations for at-risk children andbreast cancer were hurt by high-profile scandals.

The Second Mile charity founded by formerPenn State football coach Jerry Sandusky had to be closed earlier this year after Sandusky was accused and then convicted of serial sex abuse of boys. At Susan G. Komen for the Cure, there were several departures after an abortion-related political dispute over the breast cancer organization's relationship with health services provider Planned Parenthood.

The Armstrong foundation can survive by involving high-profile people other than Armstrong and by doing good work, said Penelope Cagney, an Arizona-based consultant to nonprofits.

At the foundation, a spruced-up former paper warehouse in East Austin where replicas of Armstrong's seven Tour jerseys hang on a wall, the large yellow Livestrong sign just inside the front door recalls the foundation's well-known yellow wristbands.

Inside a separate entrance, Austin-area residents who have cancer or have a loved one who does can walk in for free services including emotional support and assessment of financial options. The foundation provides similar services by phone to callers from across the country.

Armstrong, 40, founded the organization in 1997, after he was diagnosed withtesticular cancer and before he ever won the Tour de France. Since then, it has raised nearly $500 million and has evolved from a focus on testicular cancer research to addressing the needs of survivors of all cancers. It has a number of international programs.

Armstrong now is the foundation's top donor and is serving a term as chairman of the board.

"In my mind and in our minds, he's still a champion for sure," Ulman said.

For many in Austin, Armstrong is a local hero.

Marcelo Flores, 20, a University of Texas student who lost a grandfather and an uncle to cancer, recently completed a bike ride from Texas to Alaska as part of a Livestrong-sponsored group that raises money to help people with cancer.

"I still look up to him for what he's done and what he's chosen to take on after battling the disease: raising awareness, trying to help others," Flores said of Armstrong.

(Reporting by Corrie MacLaggan; Editing by Greg McCune, Peter Cooney and Lisa Shumaker)