MIAMI — In the last comprehensive review of prisoners held at Guantanamo Bay, the US government decided nearly 50 were ‘‘too dangerous to transfer but not feasible for prosecution,’’ leaving them in an open-ended legal limbo.

Now it seems many may not be so dangerous after all.

A review board that includes military and intelligence officials has been taking a hard look at these men and helping to steadily chip away at the list of indefinite detainees, who are a significant obstacle to President Obama’s push to shut down the detention center at the US military base in Cuba.

The first 23 decisions announced by the Periodic Review Board as of this month have skewed heavily in favor of the prisoners. It has unanimously cleared 19 for release, and said five will continue to be held but will be reevaluated again later.

Some of the approved have already left Guantanamo while the rest are expected to depart over the summer.

Lawyers for detainees welcomed the initial results, although they say the men shouldn’t have been held without charge for so long in the first place.

‘‘These people have not been reviewed in over six years. They have changed, circumstances have changed, and they have needed a fresh look,’’ said Pardiss Kebriaei, a lawyer for the New York-based Center for Constitutional Rights who represented a prisoner cleared by the Periodic Review Board.

The deliberations of the board are private. But David Glazier, a professor at Loyola Law School who has analyzed records of the proceedings released by the Pentagon, said the members appear to be treating past assessments of prisoners ‘‘with a healthier degree of skepticism’’ than officials did in the past.

Detainees approved for release by the board over the past two years have included a Saudi accused of being a bodyguard for Osama bin Laden who waged one of the longest hunger strikes while at Guantanamo and a Kuwaiti who was alleged to be a ‘‘spiritual adviser’’ to the Al Qaeda leader, though he would only have been about 20 at the time.

A Yemeni prisoner was cleared in January after authorities determined he was just a low-level jihadist fighter but had been mistaken for an Al Qaeda facilitator or courier with a similar alias.

In Congress, where there is strong opposition to closing the detention center, the administration is seen as moving too fast to release men some fear will resume the behavior that got them locked up.

‘‘The administration’s mad rush to push detainees on allies and partners has to stop,’’ Representative Ed Royce, a California Republican who is chairman of the Foreign Affairs Committee, said in January after 10 prisoners on the cleared list of 2010 were sent to Oman for resettlement.

There are 91 men held at Guantanamo, down from nearly 250 when Obama assumed the presidency. Those left include 36 who are cleared for release if security conditions can be met in the countries where they will settle.

Seven face trial by military commission, including five charged with planning and supporting the terrorist attack of Sept. 11, 2001. Three others have been convicted.

The Obama administration wants to close the detention center and hopes to overcome the opposition in Congress to moving any prisoners to the United States by bringing down the population at Guantanamo to what officials have called the ‘‘irreducible minimum.’’

The administration says it has no plans to go further and turn the base itself over to Cuba — a demand Obama is likely to hear during his visit to Havana starting Sunday.

The January 2010 review designated 48 men for indefinite detention under the international law of war until the end of hostilities, a vague time frame in the war against terrorist groups such as Al Qaeda.

It also said 44 other detainees should be considered for prosecution. But few can now be tried because of court rulings that limited the jurisdiction of military commissions and the ban on sending them to the United States, where they might otherwise be tried in federal court.

Men from both categories are now eligible to go before the Periodic Review Board, including some not likely to be released.

The board is made up of representatives of six agencies, including the Defense Department, Justice Department, and Office of the Director of National Intelligence. Board members consider not just past allegations, but whether the detainee could pose a threat in the future.