Under a 1998 law known as the Vacancies Reform Act, acting government officials can remain in their posts for 210 days with the full legal authority they would otherwise have with Senate confirmation, with the calendar reset to 210 days once a nominee’s name has been forwarded to the Senate. As of Monday, there are 462 days left in Mr. Bush’s term.

The president also has authority under the Constitution to make so-called recess appointments to senior jobs when the Senate is out of session — authority that President Bush has invoked far more often than his immediate predecessor, Bill Clinton.

But recess appointments often subject the White House to criticism that it is trying to circumvent the Senate confirmation process. And because there is relatively little time left in the Bush administration, there may be less pressure, or need, to consider them. The indefinite appointment of acting officials might have the same effect of circumventing Congressional oversight of nominations for what remains of the Bush presidency.

While exact comparisons are difficult to come by, researchers say that the vacancy rate for senior jobs in the executive branch is far higher at the end of the Bush administration than it was at the same point in the terms of Mr. Bush’s recent predecessors in the White House.

“You’ve got more vacancies now than a hotel in hurricane season,” said Paul C. Light, a professor of public service at New York University and one of the nation’s best-known specialists on the federal bureaucracy. “In my 25 years of studying these issues, I’ve never seen a vacancy rate like this.”

Michael J. Gerhardt, a law professor at the University of North Carolina who studies the federal appointment process, said that he believed the large number of vacancies reflected a widespread fear by Republicans that the next president, whoever it is, will be a Democrat, and that there is no job security at the top ranks of the executive branch.

“Republicans don’t have as much incentive to give up lucrative jobs in the private sector right now,” Mr. Gerhardt said.