"We promised change, and we will make changes, starting with the government itself, in its attitudes and its actions," Dr. Vázquez said in a 25-minute inaugural address. He said he would emphasize economic and social policies, "especially to the benefit of those who need them to achieve a life with dignity."

As his first official action, Dr. Vázquez announced a sweeping "Social Emergency Plan" that contains food, health, job and housing components. The program, whose cost is estimated at $100 million, is to be aimed at the hundreds of thousands of Uruguayans who have fallen below the poverty line as a result of economic crises of recent years.

Dr. Vázquez's inauguration came exactly 20 years after the restoration of democratic civilian rule in Uruguay. From 1972 through early 1985, this nation sandwiched between Brazil and Argentina was ruled by a right-wing military dictatorship that killed, jailed, tortured or forced into exile thousands of Uruguayans in order to fight off what it described as a Communist threat.

In an act that was laden with symbolism and offered an example of the "political maturity" that visiting heads of state praised, it was Senator José Mújica who presided over the swearing-in ceremony in his role as the titular head of Congress. A founder of the Tupamaro guerrilla movement that sought to lead a socialism revolution here, Mr. Mújica was jailed for virtually the entire period of the military dictatorship and was also tortured.

Offering an aside from the dais, overcome with emotion, Mr. Mújica, now committed to the parliamentary democracy he once dismissed as "bourgeois," offered his "thanks to life for having reached here." Other aging leaders of the Uruguayan left were seated in the benches reserved for members of Congress, with their eyes glistening or wiping tears from their faces.

Dr. Vázquez alluded in his inaugural speech to the widespread abuses of that era, saying there are still "dark zones in the area of human rights" that his government intends to investigate. "For the good of all, it is possible and necessary to clarify" such issues, he said, so that "the horrors of past eras never happen again."

The new president's second act in office was to restore diplomatic relations with Cuba. Ties were broken in 2002 as a result of a dispute that began when Dr. Vázquez's predecessor, Jorge Batlle Ibáñez, suggested that human rights observers be sent to Cuba to document abuses there.

Fidel Castro had been expected to arrive here today to mark the resumption of relations with a series of rallies, speeches and other public appearances. But Dr. Vázquez said Monday that the Cuban president had decided not to come "for medical reasons," presumably related to injuries he suffered in a fall last year.

In his inaugural address, Dr. Vázquez vowed that Uruguay would adopt "an independent foreign policy," in contrast to the closer ties with the United States that Mr. Batlle had sought. He said his government condemned "all forms of terrorism," favored nonintervention and peaceful resolutions of conflicts, and would insist that international financial institutions recognize "the necessity and the right to development of Uruguayan society as a whole."

"We will tolerate no outside interference in our internal affairs," Dr. Vázquez said to thunderous applause.