ROBERT S. MUELLER III has been an extraordinarily able and effective director of the FBI. So news that he may be staying on the job for another two years provides reassurance that the agency will continue to function at the highest level.

Less welcome are the legal and political implications of Mr. Mueller’s possible extended tour of duty.

The FBI director is permitted by law to serve one 10-year, non-renewable term. Congress enacted the term limit for a reason: to prevent the kind of entrenchment and consolidation of power that facilitated the abuses by the late J. Edgar Hoover, who spent four decades in charge of the bureau.

To keep Mr. Mueller in the post beyond his Sept. 4 mandatory quit date, President Obama has asked Congress to lift the 10-year cap to allow Mr. Mueller to serve until September 2013. Senior administration officials cited the upcoming 10th anniversary of the Sept. 11, 2001, terrorist attacks as justification for keeping Mr. Mueller on. “Given the ongoing threats facing the United States, as well as the leadership transitions at other agencies like the Defense Department and Central Intelligence Agency, I believe continuity and stability at the FBI is critical at this time,” the president said in a statement.

But when are continuity and stability at the FBI not critical? The country is continuously confronting one type of threat or another. Neither the Sept. 11 anniversary nor the end of Mr. Mueller’s tenure should have come as a surprise to Mr. Obama. His administration could have eliminated the timing issue if it had begun its search for a new director earlier, allowing time for a nominee to win confirmation and to shadow Mr. Mueller on the job before taking over. As it was, the president was running out of time; administration officials and those on Capitol Hill with knowledge of the process say that the president would have had to nominate a new director within the next few weeks to stand a chance of seeing that nominee confirmed before the August recess and in place at the bureau by Sept. 4.

The president’s request that Congress tinker with the 10-year term limit sets a bad precedent that should not be repeated, if Congress goes along this time. It may be the path of less resistance to retain an FBI director, easier than identifying and winning confirmation for a new nominee. But staffing an administration on schedule is part of the president’s job. For the independence and integrity of the bureau, this shouldn’t happen again.