The appearance of the letter, which was published in the International Herald Tribune, raises the prospect that some athletes may make protests during the Games, which start today at 1.08pm UK time.
With the focus of the world's media on Beijing, not only the host nation but the multinational sponsors, including McDonald's, Johnson & Johnson and Coca-Cola, will be sensitive about the spectacle being overshadowed by protests.
One of the signatories is Cuban hurdler Dayron Robles, who is competing in the high-profile 110m hurdles against China's great hope Liu Xiang.
Participants have been reminded by Jacques Rogge, the president of the International Olympic Committee, that they are not free to make political statements within the Games.
"The athletes have the full right of course to express their views outside of accredited zones," he said. "But we do not want demonstrations or propaganda, for instance, in the podium or in the Olympic village or in a venue."
Other athletes who signed the letter include the US 400m runner DeeDee Trotter and the Croatian high jumper Blanka Vlasic.
The letter is supported by Amnesty International in Germany and can be found at German website Sportsforpeace.de.
Its publication comes in the same week that protesters managed to hold up banners supporting Tibetan independence near the Bird's Nest stadium and US president George Bush issued measured criticism of China's human rights record.
The full text of the letter reads:
Dear Mr. President Hu,
We all hope that the Olympic Summer Games in China will be a great success and that the Olympic ideals will come to life.
That is why we are asking you:
- to enable a peaceful solution for the issue of Tibet and other conflicts in your country with respect to fundamental principles of human rights.
- to protect freedom of expression, freedom of religion and freedom of opinion in your country, including Tibet.
- to ensure that human rights defenders are no longer intimidated or imprisoned.
- to stop the death penalty.
China is the focus of worldwide attention. Your decision on these issues will determine the success of the Olympic Games and the image the world will have of China in the future. We are asking you to respect human rights in China in order to achieve lasting peace and reconciliation.