This April 8, 2014, file photo made during an escorted visit and reviewed by the U.S. military shows the razor wire-topped fence and the watch tower of “Camp 6” detention facility at the U.S. Naval Station in Guantanamo Bay, Cuba. (Mladen Antonov/AFP/Getty Images)

The Obama administration is accelerating its efforts to shut down the Guantanamo Bay detention center, preparing to move dozens of inmates out of the prison in coming months in a step forward for President Obama’s redoubled attempt to achieve a core national security objective before he leaves office.

U.S. officials, describing administration plans to significantly reduce the Guantanamo population over the next six months, said they are in talks with a wide range of countries that they hope will accept all 64 detainees approved for transfer.

Obama has spoken to fellow heads of government in an effort to arrange transfers, the officials said, one sign of the increased personal role they expect he will take as he inches closer to the closure of the prison.

“He does not want to leave this to his successor,” Paul M. Lewis, the Pentagon’s special envoy for shutting down Guantanamo, said in an interview.

After a virtual halt to detainee transfers in 2011-2013, officials hope to whittle the prison’s population from 132 to the mid-120s by the middle of next month. That would leave roughly half the number of detainees housed at the military complex in Cuba when Obama took office in 2009.

Defense Secretary Chuck Hagel has approved the transfer of five detainees to a host country by the end of 2014, officials said. Relocating those prisoners would bring to 28 the total number of detainees transferred this year. Five or six more prisoners are expected to be moved in the first weeks of January.

Obama remains a long way from achieving his goal of closing Guantanamo and could yet be forced to threaten executive action if he cannot overcome congressional opposition to moving or releasing detainees. But officials are optimistic that they can make significant progress in pressing other countries to accept transfers.

They are betting in particular on leaders in Latin America, who they hope will follow the lead of Uruguay, which took in six Guantanamo detainees this month. Officials also are hoping that Obama’s decision to recast U.S. policy on Cuba and recent calls by the Vatican for the prison’s closure will encourage potential host countries.

At the same time, officials still must resolve the fate of detainees from Yemen, who make up the largest portion of the remaining prisoners and are unlikely to be sent home anytime soon because of U.S. concerns about militant activity in their home country.

“We’ve been able to break the logjam,” said Clifford Sloan, who steps down this month from his position as Lewis’s counterpart at the State Department. “There’s a very clear path ahead for significant progress and ultimate closure of the facility.”

The accelerated effort to close Guantanamo is at the center of a larger effort to wind down a war-time detainee system that was created after the Sept. 11, 2001, attacks.

Also this month, the U.S. military shut down the Parwan detention facility in Afghanistan, which held a small number of prisoners on a military base near Kabul. Parwan was a final vestige of what was once a massive U.S. military operation to capture, process and house about 30,000 prisoners in Afghanistan and Iraq.

If officials can find host countries for all 64 detainees who have been cleared for transfer out of Guantanamo, they will then tackle the even harder task of dealing with the remaining prisoners. Ten detainees, including five accused of plotting the 9/11 attacks, are at some stage of a military trial process. Almost 60 more are slated to undergo official reviews that may result in some being deemed eligible for transfer. But officials expect that others — perhaps more than a dozen — will remain permanently in legal limbo, considered too dangerous for release but ineligible for trial because of insufficient or problematic evidence.

Increasingly, Obama is making a financial argument for closing the prison, which costs $400 million to $500 million a year to operate. Keeping the lights on at Guantanamo becomes even more costly on a per-detainee basis as the prisoner population falls.

Keeping Guantanamo open “is contrary to our values, and it is wildly expensive,” Obama told CNN over the weekend.

But he faces significant obstacles to closing the prison, including deep congressional opposition and turnover among his top detainee officials. Sloan and J. Alan Liotta, a senior Pentagon official on detainee policy, are stepping down around the end of the year.

There also has been friction between the White House and Pentagon over the pace of detainee transfers.

Administration officials see glimmers of hope in Congress despite lawmakers’ long-standing ban on moving prisoners to the United States for trial or detention. They hope that Sen. John McCain (R-Ariz.), who has expressed some support for closing the prison, will build momentum as he takes leadership of the Senate Armed Services Committee next year.

But Sen. James M. Inhofe (Okla.), now the committee’s top Republican, cautioned that political fault lines on Guantanamo may remain unchanged.

“Democrats and Republicans in the House and the Senate — they’re not real excited about lining up with him on these things that he’s doing,” Inhofe said. “I don’t think he’ll get by with it.”

Congressional objections are driven in part by the reappearance of some released Guantanamo detainees on the battlefield. U.S. intelligence officials have said that 17 percent of the more than 600 Guantanamo detainees released or transferred since 2002 have reengaged in militant activity and that 12 percent more are suspected of doing so.

The phenomenon is not limited to Guantanamo detainees. Abu Bakr al-Baghdadi, the head of the Islamic State, was once a prisoner at a U.S. detention center in Iraq.

Obama “is definitely putting his agenda way ahead of our national security,” Inhofe said. “He should not be doing this, but it’s consistent with other things that he’s done.”

Officials declined to say what actions Obama would, or could, take if hoped-for congressional support does not materialize. But any steps to circumvent Congress are sure to stir the kind of Republican outrage that followed the president’s recent executive action on immigration policy.

Liotta said that the risks of transferring or releasing detainees could be reduced but not eliminated. “The only way to have a zero reengagement number is to never release anybody, a position the Defense Department has never supported,” he said.

Julie Tate and Karen DeYoung contributed to this report.