President Vicente Fox endured some of the harshest criticism of his administration from his own chief of staff, who said in a resignation letter that the first lady's political ambitions are out of control and Fox is acting like the autocrats he replaced.

The missive from top adviser Alfonso Durazo (search), made public Monday, added to the storm of criticism surrounding first lady Marta Sahagun (search), and Fox's own lack of achievements.

Some have accused Sahagun's private charity foundation of receiving hidden government funding, while others object to her flirting with a presidential bid of her own in 2006.

"Since it became obvious that the first lady is running the country, I guess his [Fox's] chief of staff decided he was no longer needed," quipped Humberto Roque, a senator for the former ruling Institutional Revolutionary Party (search), or PRI.

Durazo's compared Fox to the regime of the PRI — the party that controlled Mexico's presidency from 1929 until Fox ousted it in the 2000 elections — under which outgoing presidents practically named their successors. The scheme was among the many elements of the old regime Fox vowed to erase under his "government of change."

"The desire for a government to decide who the next president will be or won't be was the original sin of the old regime," Durazo wrote in the 19-page resignation letter dated June 22. "It is my conviction that that the issue of presidential succession is operating more under the logic of the old regime, than that of a government of transition."

Of Sahagun — who, like former U.S. first lady Hillary Rodham Clinton, has been criticized for her activism and outspoken nature — Durazo wrote, "The country has certainly advanced politically, enough that it is ready for a woman to reach the presidency of the republic.

"Nonetheless, it is not prepared to have the president leave the presidency to his wife," he wrote.

The president's office issued a statement saying that it "does not share either the points of view or the reasons" cited by Durazo.

Fox named Emilio Goicoechea Luna, a business chamber leader and senator, as the new chief of staff, and Ruben Aguilar Valenzuela, a presidential analyst, as media relations chief — two positions which Durazo had held simultaneously.

He read a brief statement Monday night, saying "I want to reiterate one more time that it's time to work as a team."

"The challenges we face obligate all of us to redouble our efforts and consolidate our intelligence and beliefs to find the best means of serving Mexico," the president said.

Fox, barred from running again by constitutional term limits, has been unwilling or unable to curb the ambitions of Sahagun. She has neither formally declared her candidacy nor ruled it out, and spends her time crisscrossing the country handing out donations from her private Vamos Mexico foundation.

"Sahagun's activism has certainly caused lots of problems in Los Pinos," said George Grayson, a Mexico expert at the College of William & Mary in Williamsburg, Va., referring to the Mexican equivalent of the White House. "I suspect there will be more changes in Los Pinos in coming weeks."

But Grayson noted that Durazo's resignation was a sign of a wider malaise in Fox's administration, which has failed to fulfill its goals of job creation, economic growth or an immigration accord with the United States.

"The ship of state is sort of traveling in circles in the water, and some are jumping off the ship, and some are grabbing for the wheel," Grayson said.

Durazo claimed Fox had lost direction.

"I cannot hide my impression that power has increasing led us away from the values, principles and commitments that impelled" Fox's historic victory, he wrote. "The wave of expectations that arose from the change has receded."

Durazo's resignation could be interpreted as a nod to other leading politicians from Fox's National Action Party (search) — many of whom want the presidential nomination, and resent the advantage Sahagun enjoys in exposure and access as first lady.

But Durazo's letter also contained apparent criticisms of Fox's sparring with leftist Mexico City Mayor Andres Manuel Lopez Obrador (search), who leads polls on the 2006 race, and warned Mexico could become as unstable as Argentina, where former president Fernando De la Rua was driven from office by street riots in 2001.