In the darkened stacks of a nondescript building in the suburbs outside Washington, dozens of federal employees wearing protective gloves spend day after day sifting through millions of pages of secret documents, some of them nearly a century old.

The 70 staffers of the National Declassification Center are charged with deciding — anonymously and quietly — which of the nation’s old secrets can be laid bare for the world to see.

They have a backlog of hundreds of millions of pages marked for possible declassification, and they’re able to release those that don’t reveal information about weapons of mass destruction, harm diplomatic relations or threaten the safety of the president of the United States. But no one believes they’ll be able to make a year-end deadline set by President Barack Obama. And in the meantime, the government is classifying even more secrets.

After 3 1/2 years, just 70 million pages have been released, including the Pentagon Papers and a World War I-era recipe for secret ink. Another 45 million pages have been kept classified. The rest have yet to be fully processed.

“It’s not going to happen,” said Steven Aftergood, who directs the Federation of American Scientists Project on Government Secrecy, and is an expert on — and prominent critic of — government secrecy. “That should be a signal to everyone that the system is broken. Not even the president can make it work.”

Meanwhile, the government can’t keep up with the ever-escalating onslaught of classified documents, which are accumulating faster than ever because of the growing bureaucracy, switch to electronic data and a prevailing culture of secrecy.

Each day, federal agencies spend more time, money and effort classifying documents than declassifying them.

In fiscal year 2011, about 2,400 employees classified documents and only hundreds declassified them, according to the most recent statistics available from the Information Security Oversight Office.

Already, another 28 million pages are waiting to be reviewed at the National Declassification Center. And 103 million more pages are expected to be ready in the next five years, ensuring that the task will never end.

“We’re treading water,” said Sheryl Shenberger, a former CIA officer who is the center’s director.

Obama often boasts about being the most open president in U.S. history. On his first day in office, he offered a sweeping promise of transparency, issuing a number of executive actions to provide more openness at every level of federal government.

“My administration is committed to creating an unprecedented level of openness in government,” Obama wrote at the time. “Openness will strengthen our democracy and promote efficiency and effectiveness in government.”

While the president has tried to implement important transparency changes, he has lagged behind when it comes to meeting some of his goals, including that of keeping up with classified documents.

The federal government’s reliance on secrecy has come under intense scrutiny in recent weeks since the National Security Agency acknowledged that it gathers the telephone records and monitors the Internet activities of millions of people.

Presidents have been issuing directives on classification since Franklin D. Roosevelt. It didn’t take them long to realize they had a problem with overclassification that could leave lawmakers uninformed, the government unaccountable and the public disengaged.

Still, the process for making documents secret remains much as it was 70 years ago.

President Bill Clinton tried to tackle the issue in the 1990s by calling for the automatic declassification of what was then a backlog of 200 million pages more than 25 years old. The backlog continued.

“The culture is erring on the side of classification,” said Sharon Bradford Franklin, senior counsel at the Constitution Project, a research center that studies transparency. “The mentality is zero risk.”

Obama acted on several longtime recommendations when he created the declassification center in December 2009 to conduct “automatic” reviews while implementing revised rules for classifying and declassifying documents.

But an automatic review is anything but automatic.

First, the agency that possesses the documents reviews them. Some may be released, but many others affecting more than one agency go to the declassification center.

Center employees, joined by 100 staffers from other agencies, work in a classified area in a massive white-and-glass building, which itself requires photo identification, a walk through metal detectors to get in and a check of bags to get out.

When a visitor enters the area, a red light goes off to alert employees.

Some of the documents — stored in 200 distinct types of protective boxes — are examined one page at a time. Others may be reviewed by section.

A page can remain secret for nine reasons: if it reveals the identity of a spy, a secret code, or weapons of mass destruction or war plans; if it could harm emergency preparedness plans, diplomatic activities, or the president or vice president; or if it could violate a statute, treaty or international agreement.

Some of documents that have been released were about the Katyn Forest massacre of Polish nationals in the1940s, the Air Force’s “Reports on Soviet Air Power and Strategic Nuclear Weapons” from the 1950s and the Pentagon Papers outlining the U.S.’s involvement in Vietnam through the 1960s.

A half-dozen documents in English and French that describe secret ink formulas and methods for opening sealed letters without detection from 1917 and 1918 were thought to be the oldest ones classified when they were released in 2011.

“Dip a tooth pick in common milk and write between lines of an ordinary letter,” one document says. “The writing will appear by being ironed out with a hot flatiron.”