President Barack Obama on Friday admitted he fell short on his vow to empty the prison camps at Guantánamo, calling it a rare unfulfilled campaign promise, then stumped for closure by calling the Pentagon outpost too expensive.

``The costs of holding folks in Guantánamo is massively higher than it is in holding them in a Supermax, maximum security prison here in the United States,'' Obama said at a White House news conference a day before the Sept. 11 anniversary.

The Pentagon reports the annual cost of running the prison camps, staffed by a variety of U.S. military troops, at $116 million. With a current population of 176 war-on-terror detainees, that's more than $650,000 each.

By contrast, it costs nearly $27,251 a year to keep a prisoner in federal detention, said Bureau of Prisons spokesman Edmond Ross on Monday.

The president also defended his administration's practice of choosing to send some Guantánamo detainees to trial in civilian courts and others by the Pentagon's war court, called military commissions.

Soon after taking office, Obama signed an Executive Order setting a one-year deadline to empty the prison camps that were then holding some 260 detainees. The Jan. 22 closure date passed with business as usual in the outpost in southeast Cuba.

Friday, he cited Guantánamo as a rare failure to deliver on a campaign promise. ``You know, we have succeeded on delivering a lot of campaign promises,'' he said. ``One where we've fallen short is closing Guantánamo. I wanted to close it sooner. We have missed that deadline. It's not for lack of trying. It's because the politics of it are difficult.''

Congress blocked White House efforts to buy an Illinois federal prison and turn it into a Supermax style facility where Guantánamo captives could both be held and tried by military tribunals.

Obama blamed fear and ``political rhetoric'' but said the U.S. would be safe with Guantánamo captives on U.S. soil.

``We've got people who engaged in terrorist attacks who are in our prisons -- maximum security prisons all across the country,'' he said.

Examples include federal prisons in Florence, Colo., Marion, Ill., and Terre Haute, Ind.

He also appeared to make a pitch for a U.S. trial for confessed 9/11 conspirator Khalid Sheik Mohammed and four accused plotters, now held at Guantánamo after years in Bush-era CIA custody.

Asked whether the Sept. 11 mass murder trial will ever happen, he replied:

``We're going to work with members of Congress, and this is going to have to be on a bipartisan basis, to move this forward in a way that is consistent with our standards of due process; consistent with our Constitution; consistent also with our image in the world of -- of a country that cares about rule of law,'' he said.

``Al Qaeda operatives still cite Guantánamo as a justification for attacks against the United States. Still to this day,'' the president said. ``There's no reason for us to give them that kind of talking point.''

As part of his closure order, Obama had Attorney General Eric Holder set up a task force to assess each of the detainees then held at Guantánamo.

It found that at most 44 captives in the camps could be prosecuted by either military or civilian courts and an additional 48 captives were ``too dangerous'' to send away but ``not feasible for prosecution.''

In New York on Friday, American Civil Liberties Union executive director Anthony Romero hailed ``President Obama's recognition today that federal courts are capable of prosecuting terrorism suspects.''

But Romero called ``disappointing'' the notion that ``the president still continues to support the use of military commissions at all. The commissions are riddled with constitutional and procedural problems and their outcomes will always be subject to question,'' he said.

So far, only one captive has been sent to New York for prosecution and three have gone before military commissions.

One, Ibrahim al Qosi of Sudan, a former cook in an al Qaeda bachelors' quarters, recently pleaded guilty to war crimes in exchange for a plea deal that reportedly gives him a secret two-year term before return to his homeland.

The others are Omar Khadr, a Canadian, accused of terror murder in the grenade death of a U.S. soldier in Afghanistan in July 2002 and Noor Uthman Mohammed, a Sudanese man accused of running a terror training camp.

Khadr's trial resumes Oct. 18. Noor has a pre-trial hearing the week of Sept. 20.