WASHINGTON -- President Obama is unlikely to close the much-maligned detention facility at Guantanamo Bay in time to meet the self-imposed deadline of January, as his administration runs into daunting legal and logistical hurdles in moving the more than 220 detainees still being held there.

The difficulties in completing the lengthy review of detainee files and resolving other thorny questions mean the president's promised January deadline may slip, senior administration officials acknowledged for the first time Friday to FOX News.

The White House hopes to regain momentum -- Obama's aides have stepped up their work toward closure and the president remains as committed to closing the facility as he was when, as one of his first acts in office, he pledged to shut it down, officials told FOX News.

The White House in recent months has also shuffled its staffing for who will oversee the closure of the facility. White House Counsel Greg Craig has been replaced by senior advisers Pete Rouse, Tom Donilon and John Brennan.

But legislative difficulties and legal snares have made it inevitable that the facility will remain open for some inmates after the deadline passes.

The U.S. military prison in Cuba was created by former President George W. Bush after the Sept. 11, 2001 terrorist attacks as a landing spot for suspected Al Qaeda, Taliban and foreign fighters captured in Afghanistan and elsewhere. But it has since become a lightning rod of anti-U.S. criticism around the globe. There are approximately 225 detainees still being held at the prison.

Obama promised soon after taking office -- and many times since -- that he would close the prison, arguing that doing so would be a crucial step in restoring America's image in the world and creating a more effective anti-terror approach.

But eight months after Obama's initial pledge -- and with only four months to go before the January deadline -- a number of difficult issues remain unresolved. They include establishing a new set of rules for military trials, finding a location for a new prison to house detainees and finding host countries for those who can be released.

This has prompted top Republicans in Congress to demand that the prison stay open for the time being, saying it is too dangerous to rush the closure. Even Democrats defied the president, saying they needed more information about Obama's plan before supporting it. For the moment, Congress is denying Obama funds to shut down Guantanamo.

Senate Minority Leader Mitch McConnell, R-Ky., said Saturday Congress won't reverse its stance.

"Americans and a bipartisan majority in Congress will continue to reject any effort to close Guantanamo until there is a plan that keeps Americans as safe or safer than keeping detainees in the secure detention center," he said in a written statement. 

After Obama's promise, administration officials and lawyers began to review the files on each detainee. At issue: which prisoners can be tried, and whether to do so in military or civilian courts; which can be released to other nations; and -- the hardest question -- which prisoners are too dangerous or their cases too compromised that they must be held indefinitely.

A major complaint surfaced immediately -- that the Bush administration had not established a consolidated repository of intelligence and evidence on each prisoner. It took longer than expected to build such a database, the officials said, because information was scattered throughout agencies and inconsistent.

Those files have now been completed, and prosecutors have also concluded their initial review of the detainees and recommended to the Justice Department an unspecified number who appear eligible for prosecution, the officials told the AP. The Justice Department and the Pentagon will now work together to determine which prisoners should be tried in military courts and which in civilian ones, the officials said. They would not provide a number recommended for prosecution since it could change.

The decision on which prisoners will be prosecuted had been expected by Nov. 16, and the officials said they are on track to meet -- or beat -- that goal. Navy Capt. John F. Murphy, the chief military prosecutor, had said previously that about 65 cases are viable for prosecution.

In the meantime, Obama has kept pending several war-crimes trials that were already in progress when he took office. The administration has asked judges to suspend all proceedings to give it time to complete its review of cases.

Also, Obama has adopted some changes to the military tribunals, but wants Congress to enact more to address criticism that the courts favor the prosecution and will not withstand constitutional challenges. That legislation is moving forward on Capitol Hill, but is not complete.

The government also must decide where inside the U.S. to move the detainees, and that highly fraught choice still has not been made, the officials said. A maximum security prison in Standish, Mich., and the military penitentiary at Fort Leavenworth in Kansas are under consideration as possible locations. Whatever facility is chosen, the Pentagon will have to make improvements necessary to safely house the prisoners.

The officials noted that the U.S. prison system already holds 216 people convicted as international terrorists.

Another hurdle in the effort to close the prison is the problem of finding countries willing to take in those detainees deemed eligible for release. The administration so far has transferred 14 prisoners to other countries, the officials said.

The administration will not "voluntarily release" any detainee inside the United States, the officials said. But this does not address what might happen if any of the detainees who are tried are found innocent -- a subject of considerable angst about Obama's plans, both in Congress and among the public. However, the U.S. could -- and likely would -- seek to transfer those people to other countries in that case, as none is a U.S. citizen.

FOX News' Major Garrett and The Associated Press contributed to this report.