HAVANA, Jan 22 (Reuters) - Cuba's Fidel Castro, ailing and 82, signaled on Thursday that thoughts of mortality were on his mind as he wrote in an Internet column about death and failing health.

In his second column in as many days, after a prolonged silence that fueled speculation about his health, Castro also praised new U.S. President Barack Obama, who he said had become "a living symbol of the American Dream."

The former leader had been rumored to be in worsening condition because he had not written a column since Dec. 15 after averaging nine a month in 2008.

He has not been seen in public since intestinal surgery in July 2006 that forced him to turn over power to brother Raul Castro, so the frequency of his columns have become an informal barometer of his physical state.

But he wrote that he had made a conscious decision to reduce the number of columns, or reflections as he calls them, because he did not want "to interfere or get in the way" when government leaders are grappling with the world financial crisis.

"I am fine, but I insist that none of them should feel themselves bound by my reflections, my serious state of health or my death," he said.

He wrote that he had had the "rare privilege" of observing events for a long time, but said, without explaining, "I expect I won't enjoy that privilege four years from now, when the first presidential term of Obama has concluded."

Castro's columns are usually filled with vitriol for the United States but he has been complimentary of Obama previously and in the two latest pieces.

He praised him on Thursday for ordering the closure of the prison at Guantanamo Bay, constructed by the Bush administration to house and try men suspected of terrorist activities.

"Nobody could doubt the sincerity of his words when he affirmed that he would convert his country into a model of liberty, respect for human rights in the world and the independence of other peoples," he wrote.

"The intelligent and noble face of the first black president of the United States since its founding ... had transformed itself under the inspiration of Abraham Lincoln and Martin Luther King to become a living symbol of the American Dream," he said.

But Castro interjected a note of skepticism, asking what Obama will do "when the immense power he has taken in his hands is absolutely useless to overcome the unsolvable, antagonistic contradictions of the (U.S.) system?" (Editing by Mohammad Zargham)

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