WASHINGTON  Rebuffed this month by skeptical lawmakers when it sought finances to buy a prison in rural Illinois, the Obama administration is struggling to come up with the money to replace the Guantánamo Bay prison.

As a result, officials now believe that they are unlikely to close the prison at Guantánamo Bay, Cuba, and transfer its population of terrorism suspects until 2011 at the earliest  a far slower timeline for achieving one of President Obama’s signature national security policies than they had previously hinted.

While Mr. Obama has acknowledged that he would miss the Jan. 22 deadline for closing the prison that he set shortly after taking office, the administration appeared to take a major step forward last week when he directed subordinates to move “as expeditiously as possible” to acquire the Thomson Correctional Center, a nearly vacant maximum-security Illinois prison, and to retrofit it to receive Guantánamo detainees.

But in interviews this week, officials estimated that it could take 8 to 10 months to install new fencing, towers, cameras and other security upgrades before any transfers take place. Such construction cannot begin until the federal government buys the prison from the State of Illinois.