Washington, D.C. ? As the chief federal trial judge in Manhattan, Michael Mukasey approved secret warrants allowing government roundups of Muslims in the days after the Sept. 11 attacks.

Six years later, the man President Bush wants to be attorney general acknowledged that the law authorizing those warrants “has its perils” in terrorism cases and urged Congress to “fix a strained and mismatched legal system.”

Mukasey’s caution about the material witness law probably will please Democrats who control the Senate Judiciary Committee. At confirmation hearings set to begin Wednesday, they plan to press the retired federal judge about the Bush administration’s terrorist detention policy.

The committee chairman, Sen. Patrick Leahy, long has criticized the government’s use of the warrants. They allowed the FBI to detain, without charges, an estimated 70 people, all but one of whom were Muslim, as witnesses after the terrorist attacks in 2001.