CARACAS, Venezuela — After a year shadowed by his cancer treatment, in which he appeared weakened and his strident voice was muted, Hugo Chávez, the colorful and obstreperous Venezuelan president who has made a habit of defying and taunting the United States, has found his swagger again.

This month he hosted President Mahmoud Ahmadinejad of Iran, embracing him as a friend, joking about nuclear weapons and laughing off the charge by the United States and its allies that Iran was seeking to develop an atomic bomb. He vowed to pull out of a World Bank arbitration process that could force Venezuela to pay billions of dollars to foreign companies, like Exxon Mobil, whose property he has nationalized.

And, in one stroke, he found a way to irk both Washington and his political opponents at home, appointing a new defense minister who has been accused by the United States of supporting the drug trafficking activities of a Colombian rebel group classified as a terrorist organization by the State Department.

Throughout the summer and fall, Mr. Chávez appeared uncharacteristically frail, when he showed up in public at all. He curtailed a once-busy schedule and stopped conducting his weekly Sunday television program, Aló Presidente, which for years had helped rouse his core supporters and shape the national dialogue.

But now that he says he has beaten cancer, he is asserting himself as the dominant figure in a tough campaign for re-election this year. As if to broadcast his renewed vigor, Mr. Chávez spoke for more than nine hours in his annual address to the National Assembly on Jan. 13, never sitting down and pausing only to take questions from legislators.

Commentators said that the speech, the equivalent of a State of the Union address, was his longest ever (last year’s version was a mere seven and three-quarters hours) and that Mr. Chávez was intent on showing voters and politicians in his own party and the opposition that his powers were not diminished.

He said as much himself, concluding his speech by reading a passage from Nietzsche on the importance of will in overcoming obstacles. He ended with his own words: “Here I am. I have returned.”

It was “vintage Chávez in campaign mode,” said Michael E. Shifter, president of Inter-American Dialogue, a nonpartisan policy group focused on the Western Hemisphere. “He’s basically saying, ‘I’m back, I’m in full control, this is the old Chávez.’ ”

Mr. Chávez has governed Venezuela for 13 years. He often picks fights with the United States, portraying it as an imperial bully and using his defiance to rally supporters at home and abroad. And he has pushed an increasingly aggressive agenda to establish his own brand of socialism in Venezuela, which includes the nationalization of businesses large and small, and programs aimed at fighting poverty.

But he was forced to check his stride. In June, he underwent surgery for his cancer and then began chemotherapy, shuttling back and forth to Cuba, where he received much of his treatment. His absence left a void, animating the opposition, revealing divisions within his own party and raising the question of whether he would still be the force he once was, if he recovered at all.

“The president was absent from the debate,” said Elsa Cardozo, a professor of international studies at the Central University of Venezuela. “It created room to think about a political future without Chávez, or with a Chávez diminished in his ability to bring together and control his supporters.”

At the same time, popular discontent with his government has grown over widespread electrical failures and rampant violent crime. Venezuela’s regional influence has also waned, following a period when its economy struggled and neighboring Brazil exerted itself as the continent’s powerhouse.

Mr. Chávez has never disclosed what form of cancer he had and speculation rages that he is much sicker than he has let on, raising doubts about his ability to campaign for re-election or govern for another term.

But in recent weeks Mr. Chávez has sharpened his tone and filled out his schedule. He rolled out new social programs in December that are sure to shore up support among the poorest Venezuelans, including a program that gives poor households about $100 a month for each child.

He held a meeting of heads of state from countries in Latin America and the Caribbean last month. And he revived his old rivalries, suggesting that the United States may have found a way to induce cancer in people it considered enemies, pointing to several heads of state in the region who, like himself, had received a diagnosis of cancer.

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