The ailing Fidel Castro did not show up to a huge military parade Saturday marking the 50th anniversary of the founding of Cuba's Revolutionary Armed Forces, fueling speculation about the severity of his condition and the possibility he may not return to power.

Acting President Raul Castro, who is Fidel's younger brother and the island's defense minister, led the event instead, giving a speech reaching out for dialogue with the U.S. government, which has a decades-old trade and travel embargo against the communist-run island.

"We take this opportunity to once again state that we are willing to resolve at the negotiating table the long-standing dispute between the United States and Cuba ... as long as said resolution is based on the principle of equality, reciprocity, noninterference and mutual respect," Raul Castro said.

"In the meantime, after almost half a century, we are willing to wait patiently until the moment when common sense prevails in Washington power circles," he said.

The acting president still criticized the United States, particularly its involvement in the Iraq war and attempts to "annex Latin America" through its regional trade policies. He did not explain his brother's absence in his half-hour speech.

Raul Castro also used the event to underscore cohesion among the Cuban people, the armed forces and the Communist Party — a recurring theme among officials in recent days. "This unity is our main strategic weapon, which has made it possible for this small island to resist and overcome so many aggressions from imperialism and its allies," he said.

Cubans and Castro supporters as well as foes around the world had speculated all week whether the elder Castro brother, recovering from intestinal surgery, would show. The military event, which lasted about two hours, culminated five days of events — none of which were attended by Castro — to celebrate his birthday.

The Cuban leader turned 80 on Aug. 13 but delayed the celebrations to give him time to recover from surgery two weeks earlier for intestinal bleedings. He has not been seen in public since July 26, and few details about his condition have been released by Cuba's government.

"It is fine that he didn't come, so that he can recuperate," said Magda Avila, a 70-year-old army veteran at Saturday's march.

Cuban officials insist Castro is recovering, but U.S. officials say they believe he suffers from some kind of inoperable cancer and won't live through the end of 2007. He has appeared thin and pale in photographs and videos released by the government since he temporarily ceded power to his brother.

In the first major military parade held in Havana in a decade, tens of thousands of Cubans marched behind anti-aircraft missiles, tanks and other armored vehicles while MiG fighter jets and helicopter gunships flew overhead at the parade. The crowd of loyalists was more subdued than in other mass events presided by Fidel Castro.

Hundreds of elderly former combatants from the revolutionary struggle sat near the podium where Raul Castro spoke. Thousands of marching troops launched the parade, including special forces in red berets, militia men in blue uniforms and horseback riders wearing the white dress uniform of 19th-century Cuban independence fighters.

The parade's most obvious purpose was to warn the United States against taking advantage of Castro's illness to attack the island. In the last 15 years the Cuban military has taken on a purely defensive role, and is trained to repel invaders.

It also commemorated what Raul Castro called "a transcendental act in our history."

Cuba's Revolutionary Armed Forces, which replaced the military that existed before the Cuban Revolution, traces its roots to Dec. 2, 1956, when 82 rebels landed on the island on a yacht — the Granma — that sailed from Mexico.

Fewer than two dozen rebels, the Castro brothers included, survived a battle with then-President Fulgencio Batista's troops after the landing. From the mountains, they launched a guerrilla war, which triumphed on Jan. 1, 1959.

Fidel Castro purportedly sent a message to those celebrating his birthday earlier this week, telling a crowd of 5,000 supporters at the opening event Tuesday at a Havana theater that he was too sick to meet with them.

"I direct myself to you, intellectuals and prestigious personalities of the world, with a dilemma," said a note read at the event. "I could not meet with you in a small locale, only in the Karl Marx Theater where all the visitors would fit, and I was not yet in condition, according to the doctors, to face such a colossal encounter.

"My very close friends, who have done me the honor of visiting our country, I sign off with the great pain of not having been able to personally give thanks and hugs to each and every one of you," the note read.

More than 1,300 politicians, artists and intellectuals from around the globe were attending the tribute to the man who governed Cuba for 47 years. Bolivian President Evo Morales, Haitian President Rene Preval, Nicaraguan President-elect Daniel Ortega and Colombian Nobel laureate Gabriel Garcia Marquez were among the guests of honor.