Published: Jan 01, 2011 10:27 PM EST
Updated: Jan 01, 2011 8:16 PM EST

BRASILIA, Brazil (AP) - Dilma Rousseff was sworn in as Brazil's first female president Saturday, capping a rapid political trajectory for the career technocrat and former Marxist rebel who was imprisoned and tortured during the nation's long military dictatorship.

Rousseff, 63, takes the helm of Latin America's largest nation, which has risen both financially and politically on the world stage under outgoing leader Luiz Inacio Lula da Silva.

Silva leaves office as the nation's most popular president with an approval rating that hit 87 percent in his last week in office.

Rousseff was his hand-chosen successor. Rousseff, wearing a white skirt and matching jacket, took the oath of office alongside Vice President Michel Temer in the national Congress. A heavy rain swept over Brazil's capital, Brasilia, as Rousseff arrived at the Congress in a 1953 Rolls Royce, her hand waving out the window to the thousands of cheering onlookers. Her security detail comprised six young women, clad in black and running alongside the car through the downpour.

Rousseff takes on the formidable task of maintaining Brazil's momentum.

In the eight years under Silva, Brazil sharply cut poverty while its economy boomed, and it has increased its political clout on the global stage. Brazil will host the 2014 World Cup and is expected to be the world's fifth-largest economy by the time the 2016 Olympics come to the nation.

Huge challenges also await Rousseff, who served as Silva's energy minister before becoming his chief of staff, where her tough managerial manner earned her the moniker "Iron Lady."

In addition to sweeping improvements Brazil needs in its infrastructure, security and education, she confronts the danger of following the charismatic Silva, who leaves office with an 87 percent approval rating.

"Dilma will have to meet high expectations that the country is on an upward trajectory and life will continue to get better for the average Brazilian," said Michael Shifter, president of the Inter-American Dialogue. "That will not be an easy challenge."

Shifter said it could prove difficult for Brazil to maintain the pace of success it saw under Silva.

The external economic scenario could worsen, cutting into strong demand for Brazil's agricultural and industrial exports, particularly if anything should dampen China's growing appetite for Brazil's goods. The Asian nation this year passed the U.S. as Brazil's biggest trading partner.

And Rousseff will need a strong economy to improve the nation's woeful airports, ports, and roads - all vital in transporting Brazil's raw goods to market and in hosting the World Cup and the Olympics - events Brazilians hope will bolster their newfound image as a nation that gets things done.

Rousseff also will have to handle the unwieldy political coalitions required to govern Brazil. Silva, with his vast experience, his unique popularity and by sheer force of will was able to satisfy the leftist elements in his Workers Party, while at the same time employing orthodox economic policies to calm the business community that fretted early on about his socialist roots.

Rousseff lacks Silva's political acumen and charisma and it is not yet known if she will be able to command the far-flung components of the Workers Party while also keeping other factions happy in a coalition government.

But as Silva's hand-chosen successor, and a Cabinet member of his government from its start in 2003, Rousseff has the power of continuity going for her.

"Dilma represents a great novelty in Brazil," said Alexandre Barros, a political analyst with the Early Warning political risk group in Brasilia. "Before, every new government brought with it huge uncertainty. Everybody would shout about how Brazil was going to ruins. But now, with Rousseff, no. She represents what we've already seen."

(Copyright 2011 by The Associated Press. All Rights Reserved.)