A U.S.-backed resolution to condemn the island's record is usually presented at every spring meeting in Geneva of the U.N. Human Rights Commission, which this year was to open Monday and run through April 22.
No resolution targeting the island has emerged this year. But Cuba expects such a proposal will be presented and considered in mid-April.
"We urge the governments of the commission's member countries to not permit (the resolution) to be used to legitimize the anti-Cuban aggression of the administration of (U.S. President George W.) Bush," the letter said.
Washington maintains a four-decades-old trade embargo against the island, with trade and travel restrictions being steadily tightened in recent years.
Nobel Peace Prize laureates such as Adolfo Perez Esquivel of Argentina and Rigoberta Menchu of Guatemala signed the letter, as did South Africa's Nadine Gordimer and Portugal's Jose Saramago, both recipients of the Nobel Prize in Literature.
Among American signatories were actor Danny Glover, author Alice Walker and historian and activist Howard Zinn. Other international figures included filmmaker Walter Salles of Brazil, the music group Manu Chau and France's former first lady, Danielle Mitterrand.
The letter said the U.S. government has no moral authority to criticize Cuba's human rights record after its own scandals over treatment of terror suspects at prisons in Iraq and the U.S. naval base at Guantanamo Bay.
This "nobel and important" declaration comes as "humanity lives very difficult and even dangerous moments," Roberto Retamar, director of Casa de las Americas, Cuba's center of Latin America culture, told a news conference.
A U.S. report on rights practices in Cuba released last month acknowledged there were no extrajudicial killings or disappearances of opponents on the island last year. But it took Fidel Castro's government to task for violations of civil and political rights such as freedom of speech, press, assembly, as well as the imprisonment of dissidents.
Some who signed the letter had criticized Cuba when the government sentenced 75 political opponents to long prison terms in the spring of 2003.
Asked about the dissidents, Retamar said, "I would like for all prisons to be empty," but said those imprisoned were "mercenaries" who deserved to be jailed for working with Cuba's enemies.
Last year's resolution criticizing Cuba narrowly passed, adopted by 22 votes to 21, with 10 abstentions.