MEXICO CITY - (AP) -- President Vicente Fox rallied to the defense of first lady Marta Sahagún on Thursday after Congress ordered an audit of a charity that she runs, and legislators proposed a law that would prevent her from running for the presidency in 2006.

  The moves capped more than a week of heated debate over Sahagún's involvement in politics and her role as head of the Vamos Mexico charity foundation, which has been tardy in presenting a detailed accounting of its income and expenses.

  Fox on Thursday denied accusations that executive branch funds may have been used to support Sahagún's foundation.

  ''This investigation, and any other investigation that aims to make government accounts more transparent, is welcome,'' Fox said in broadcast remarks. ``This administration has nothing to hide, and thus nothing to fear.''

  ''We do disagree, however, when these audits are used with ill intent to sow mistrust in the public's mind,'' Fox said. He added that presidential guards did accompany Sahagún to charity events to protect her but that all of the logistic costs for those events were paid by the foundation, not taxpayers.

  Fox said the executive branch's own audit of Sahagún's participation in presidential trips had yielded four ''observations'' by auditors -- in other words, four recommendations that did not involve accusations of wrongdoing.

  On Wednesday, Congress' leadership body -- which sits when the full legislature is in recess -- ordered the country's general accounting office to investigate whether any of the foundation's employees were being paid out of presidential funds.

  The criticism of Sahagún may backfire by giving her more media attention and making her appear the victim of a smear campaign.