WASHINGTON » In ordering the federal government to acquire an Illinois prison to house terrorism suspects who are currently held at Guantanamo Bay, Cuba, President Barack Obama yesterday took a major step toward shutting down the military detention facility that its detractors say had become a potent recruitment tool for al-Qaida.

But even before White House officials had released a letter informing Gov. Patrick J. Quinn of Illinois of the plans to send a “;limited number”; of Guantanamo detainees to the Thomson Correctional Center, an empty super-maximum-security prison in northwestern Illinois, Republicans were gearing for what could be an emotional fight on Capitol Hill.

“;The administration has failed to explain how transferring terrorists to Gitmo North will make Americans safer than keeping terrorists off of our shores in the secure facility in Cuba,”; Sen. Mitch McConnell of Kentucky, the Senate Republican leader, said in a statement. Rep. John Boehner of Ohio, the House Republican leader, told reporters he would not vote to “;spend one dime to move those prisoners to the U.S.”;

Administration officials acknowledged that the move will require congressional approval, since Congress now bars Guantanamo detainees from being brought onto American soil unless they face prosecution, and some of the detainees may be indefinitely confined without being tried. But one administration official said that Democrats, who control both houses, were planning to lift that restriction if the administration came up with an acceptable plan for closing the military prison at Guantanamo.

Obama declared shortly after his inauguration that he would close the facility—a signature component of the Bush administration's counterterrorism policy—within a year. But dealing with the detainees at the prison has proved difficult, and he has acknowledged that he will most likely miss that deadline.

The officials, speaking on grounds of anonymity under White House rules, said that they have not yet determined how many Guantanamo detainees will be sent to Thomson, nor have they set a timetable for moving them there. But several administration officials put the probable number of transferred detainees at about 100.

There are currently about 210 detainees at Guantanamo, administration officials said. Since Obama took office, about 30 inmates have been transferred to other countries, and administration officials have said they hope that another 100 prisoners may also be sent overseas.

The officials said they plan to prosecute more than 40 of the remaining detainees in either military or civilian courts. Five have already been designated to face military commissions and five will be tried in civilian courts, including Khalid Sheikh Mohammed, the chief planner of the 2001 attacks, who will face trial in New York.

As many as several dozen prisoners would be held in indefinite detention in a category the Obama administration refers to as “;law of war”; detainees—those deemed ineligible for prosecution but too dangerous to release. Though the administration has not yet identified who would be included in that category, lawyers for many of the detainees have filed habeas corpus petitions in federal court challenging their detention.

Addressing critics' concerns that those prisoners could be freed inside the United States, administration officials said that if any of the habeas appeals succeeded, the detainees would be transferred out of the country or brought to trial.

White House officials said moving terror suspects to Illinois would not put Americans at risk. They walked through a list of upgrades that the Thomson prison will get—an additional security perimeter among them—and added that the move would also bring an additional 3,000 jobs.

Most of the prison would house ordinary high-security inmates, but a part would be leased to the Defense Department to hold the terror suspects. Administration officials said in a conference call with reporters that the two parts of the facility would be managed separately.

In the letter to Quinn, the administration promised that federal inmates at Thomson would not interact with Guantanamo detainees.

“;Not only will this help address the urgent overcrowding problem at our nation's federal prisons, but it will also help achieve our goal of closing the detention center at Guantanamo in a timely, secure, and lawful manner,”; said the letter, signed by Secretary of State Hillary Rodham Clinton, Defense Secretary Robert Gates, National Intelligence Director Dennis Blair and Attorney General Eric Holder.

It was not immediately clear how the government would pay for the prison and the required upgrades, but White House officials have floated the idea of including financing for it in the 2010 military appropriations bill.

The decision to move the detainees to the United States generated criticism from both sides of the political aisle. Sen. John Cornyn, R-Texas, called it “;deeply troubling”; in a statement. “;This move will put our citizens in unnecessary danger,”; he said, “;and that is unjustifiable and unacceptable.”;

From the left, Amnesty International was equally critical. “;The only thing that President Obama is doing with this announcement is changing the ZIP code of Guantanamo,”; said Tom Parker, Amnesty International USA policy director.

“;The detainees who are currently scheduled to be relocated to Thomson have not been charged with any crime,”; Parker said. “;In seven years, the U.S. government, including the CIA and FBI, have not produced any evidence against these individuals that can be taken into a court of law.”;

Earlier proposals to move detainees to Kansas, Michigan and South Carolina have been rejected by local political leaders. The difficulty in finding where to move them is a significant reason why the Obama administration has been unable to keep Obama's pledge to close the Cuban prison by next month.

Earlier this year, lawmakers barred the Obama administration from releasing any Guantanamo prisoners into the country. More recently, Congress kept in place the ban on releasing them in the United States, but authorized transfers for prosecution to military or civilian courts, though it required 45-day advance notification of all such moves.