BUENOS AIRES (By Larry Rohter, NYTimes) November 29, 2005 — Bringing an abrupt end to an alliance that had grown uneasy, even contentious, Argentina's president, Néstor Kirchner, yesterday fired his economy minister, Roberto Lavagna, the main architect of the country's recovery from the worst economic crisis in its history.

Mr. Kirchner's chief of staff announced the change at the end of a news briefing in Buenos Aires at which new foreign, defense and social welfare ministers were also designated. No explanation was given for Mr. Lavagna's departure, but at a news conference of his own a couple of hours later, he made it clear that he had been asked to leave.

"The president signaled to me that he had concluded it was time to begin a new phase," Mr. Lavagna said. "The consequent logic was that I put my post at his disposal, which I did immediately."

Mr. Lavagna's successor is Felisa Miceli, president of the state-run Banco de la Nación and the first woman to hold the economy portfolio. Ms. Miceli, 51, an economist who once worked for Mr. Lavagna's consulting firm, is closely identified with many policies he has advocated, but is seen as lacking his political influence and independence.

Domestic and foreign investors quickly made clear that they harbored doubts about the change. The Buenos Aires benchmark stock index fell 4.49 percent in heavy trading, the Argentine peso declined against the dollar, and Argentina's country-risk index rose.

"To change ministers at this moment is very risky," Miguel Schiaritti, head of the Chamber of Commerce and Industry, told La Nación's news service. "The outgoing official had shown himself to be the right man, after many years, to reach the targets and achieve the economic conditions we now have."

President Kirchner was virtually unknown when he took office in May 2003 after having won less than a quarter of the popular vote. Hoping to gain credibility and avoid market nervousness, he announced before he was sworn in that he intended to keep Mr. Lavagna in place, cementing a partnership that reached its peak in March, when Argentina announced a debt settlement in which its creditors agreed to take as little as 30 cents on the dollar.

But in midterm congressional elections last month, President Kirchner's slate of candidates won a decisive victory, considerably reducing his dependence on Mr. Lavagna. Mr. Kirchner has since moved to consolidate his authority while at the same time showing signs of wanting to steer his government leftward.

At a meeting of Western Hemisphere leaders in Argentina early in November, President Vicente Fox of Mexico criticized Mr. Kirchner, saying he had not worked hard enough to advance the cause of free trade and had thus embarrassed President Bush. Then, last week, Mr. Kirchner flew to Caracas and signed a series of agreements with Hugo Chávez, Venezuela's leftist leader and Washington's leading critic in the region.

New doubts about Argentina's willingness to negotiate an agreement with the International Monetary Fund have also emerged. At the summit meeting, Mr. Kirchner asked Mr. Bush to lobby with the I.M.F. on his behalf for more favorable terms, but was rebuffed. "My reading is that Argentina is continuing to deepen a tendency to go left," an economist, José Luis Espert, told La Nación. "Without Lavagna, Kirchner now has no one to rein him in."

Mr. Lavagna, 63, took the economy minister's post in April 2002 with the Argentine economy in ruins. The currency had collapsed a few months earlier, losing nearly 75 percent of its value, while bank accounts were frozen and the government had reneged on payment of more than $100 billion in debts, the largest government default in history.

The economy shrank 11 percent that year but has grown by as much as 8 percent each year since then. Exports, employment and investment have all expanded, all without the I.M.F.'s stamp of approval on government policies.

Recently, though, Mr. Kirchner and Mr. Lavagna quarreled over how best to confront a spurt of inflation. Last week, Mr. Lavagna complained of the "cartelization" of public works projects, which carried an implication of corrupt price fixing and large cost overruns that appear to have enraged Mr. Kirchner.