WASHINGTON — President-elect Barack Obama is preparing to issue an executive order his first week in office — and perhaps his first day — to close the U.S. military prison at Guantanamo Bay, according to two presidential transition team advisers.

It's unlikely the detention facility at the Navy base in Cuba will be closed anytime soon. In an interview last weekend, Obama said it would be "a challenge" to close it even within the first 100 days of his administration.

But the order, which one adviser said could be issued as early as Jan. 20, would start the process of deciding what to do with the estimated 250 al-Qaida and Taliban suspects and potential witnesses who are being held there. Most have not been charged with a crime.

The Guantanamo directive would be one of a series of executive orders Obama is planning to issue shortly after he takes office next Tuesday, according to the two advisers. Also expected is an executive order about certain interrogation methods, but details were not immediately available Monday.

The advisers spoke on condition of anonymity because they were not authorized to speak publicly about the orders that have not yet been finalized.

Obama transition team spokeswoman Brooke Anderson declined comment Monday.

The two advisers said the executive order will direct the new administration to look at each of the cases of the Guantanamo detainees to see whether they can be released or if they should still be held — and if so, where.

Many of the Guantanamo detainees are cleared for release, and others could be sent back to their native countries and held there. But many nations have resisted Bush administration efforts to repatriate the prisoners back home. Both Obama advisers said it's hoped that nations that had initially resisted taking detainees will be more willing to do so after dealing with the new administration.

What remains the thorniest issue for Obama, the advisers said, is what to do with the rest of the prisoners — including at least 15 so-called "high value detainees" considered among the most dangerous there.

Detainees held on U.S. soil would have certain legal rights that they were not entitled to while imprisoned in Cuba. It's also not clear if they would face trial through the current military tribunal system, or in federal civilian courts, or though a to-be-developed legal system that would mark a hybrid of the two.

Where to imprison the detainees also is a problem.

Obama promised during the presidential campaign to shut Guantanamo, endearing him to constitutional law experts, civil libertarians and other critics who called the Bush administration detentions a violation of international law.