The administration argues that a new law strips courts of their jurisdiction to hear detainee cases.
"In other words," says CBS News correspondent Wyatt Andrews, "the two other branches of government have told the court to lay off Guantanamo and today the Supreme Court said 'No.'"
The justices took the action without comment along with other end-of-term orders. In April, the court turned down an identical request, although several justices indicated they could be persuaded otherwise.
The move is highly unusual.
"Just because the justices have agreed to hear the cases doesn't mean they will automatically rule against the government and for the detainees," CBS News legal analyst Andrew Cohen says, though he adds the news will leave the White House "concerned."
The court did not indicate what changed the justices' minds about considering the issue. But last week, lawyers for the detainees filed a statement from a military officer in which he described the inadequacy of the process the administration has put forward as an alternative to a full-blown review by civilian courts.
"This is a stunning victory for the detainees," said Eric M. Freedman, professor of constitutional law at Hofstra Law School, who has been advising the detainees. "It goes well beyond what we asked for, and clearly indicates the unease up there" at the Supreme Court.
Gordon Johndroe, a spokesman for the National Security Council, said that "we did not think that court review at this time was necessary, but we are confident in our legal position."
The Justice Department issued a similar statement: "We are disappointed with the decision, but are confident in our legal arguments and look forward to presenting them before the Court."
Tom Wilner, an attorney for Guantanamo detainees, says the court is finally confronting the legal black hole of Guantanamo, reports Andrews. Of the 375 detainees, only 10 have been charged with a crime, and the evidence against the rest, Wilner says, can be farcical.
"The government has admitted that most of the evidence is simply second- or third-hand hearsay ... but for many people, there is no evidence," says Wilner.
Five of the nine justices must agree to take a case that previously has been denied a hearing, according to an authoritative text on the Supreme Court.
The case is expected to be heard in the fall.
"I would not be surprised if five or more justices were willing again to tell the White House and Congress to try yet again to get it right," Cohen says.
In February, the U.S. Circuit Court of Appeals for the District of Columbia upheld a key provision of a law the Bush administration pushed through Congress last year stripping federal courts of their ability to hear the detainees' challenges to their confinement.
On April 2, the Supreme denied the detainees' request to review the February appeals court ruling.
The detainees then petitioned the court to reconsider its denial.
Dismissing the petitions would be "a profound deprivation" of the prisoners' right to speedy court review, lawyers for the detainees said.
The administration asked that the detainees' Supreme Court petitions be thrown out.
Many of the 375 detainees have been held at Guantanamo for five years.
In recent months, the main arena in the legal battle over the detainees has been the U.S. Circuit Court of Appeals for the District of Columbia.
The appeals court is considering how to handle the detainees' challenges to tribunals that found them to be enemy combatants, leaving them without any of the legal rights accorded prisoners of war.
The detainees' attorneys want the appeals court to allow a broad inquiry questioning the accuracy and completeness of the evidence the Combatant Status Review Tribunals gathered about the detainees, most of it classified.
The Justice Department has been seeking a limited review, saying that the findings of the military tribunals are "entitled to the highest level of deference."
An Army reserve officer and lawyer who played a key role in the enemy combatant hearings at Guantanamo Bay says tribunal members relied on vague and incomplete intelligence while being pressured to rule against detainees, often without any specific evidence. The officer's affidavit, submitted to the Supreme Court last Friday, is the first public criticism by a member of the military panels that determine whether detainees will continue to be held.
"I suspect that the disclosure about the corrupted CSRT proceedings and the very restrictive government view of what the detainees can do in the lower courts led the justices to conclude that they should take up these issues," said Washington attorney David Remes, who represents 18 detainees.
"The court's decision to hear the cases brings the detainees one step closer to receiving their day in court," said Remes.
The operation of Guantanamo Bay has brought global criticism of the Bush administration and condemnation from Democrats on Capitol Hill.
The cases are Boumediene v. Bush, 06-1195, and Al Odah v. U.S., 06-1196.