Two years have passed since Congress approved a law allowing federal employees to work part-time after earning retirement eligibility.

The federal workforce, with hundreds of thousands contemplating retirement, greeted the first-of-its kind opportunity with enthusiasm.

But not a single federal employee has been able to take advantage of  the “phased retirement” law, because the Office of Personnel Management still has not issued regulations covering the specifics. The popular program is stuck in bureaucratic limbo.

“This is a good policy that everyone was behind,” said Jessica Klement, legislative director for the National Active and Retired Federal Employees Association. “It saves money. The people who want this really want to to it. So what’s the problem?”

OPM Press Secretary Nathaly Arriola said in a statement that the agency is “working hard on the rule” and hopes the regulations will be done by the time the fiscal year ends in October.

“We want to make sure we get it right and we will have an update soon,” the statement said, without explanation for what ‘s taking so long.

The program has actually been under discussion since 2010. That’s when the Obama administration proposed phased retirement to Congress as part of a larger bill to reform federal hiring practices. The part-time provision passed in an unrelated transportation bill in July 2012.

The broad outlines are these: Employees can partially retire and draw on half of their pensions while continuing to work part time. OPM issued draft regulations more than a year ago that said participants would need 20 years of experience and have to be eligible to retire immediately. And they would need to spend  at least 20 percent of their time mentoring their successors or other employees.

But would-be retirees are anxiously awaiting other details: Will agencies limit the number of employees in an office who can participate? Will the government cap the number of years someone can work part-time?

Rules to implement the law were on a fast track under former OPM Director  John Berry.  But a December 2013 deadline came and went.

The delays are familiar. It can take years for federal agencies to write rules that accompany many laws passed by Congress; the fine print that allows them to be implemented can be controversial.

For example, draft regulations to limit the political activities of nonprofit advocacy groups following the Internal Revenue Service tea party controversy were released in November 2013. A record 150,000 people weighed in during a public comment period.

The IRS is now reworking the proposal, but doesn’t expect to have it done until early 2015.

A few years ago, OPM made changes to its programs that bring young people into government. The regulations took more than two years to get on the books.

Rules on part-time retirement don’t seem particularly controversial. Everyone agrees on the importance of  ensuring that expertise isn’t suddenly lost across government when veteran employees leave.

This program also will save the government an estimated $425 million over 10 years.

Near Las Cruces, New Mexico, David Knapp is anxiously awaiting news on whether he’ll be eligible to work part-time for the U.S. Army when he turns 56 next March.

Knapp, a meteorologist and retired Air Force reservist, is a branch chief at the White Sands Missile Range, working with a team that devises weather forecasting technologies for the battlefield.

His Air Force pension won’t kick in until he’s 60, and in the meantime, he’d like the freedom of retirement but the guarantee of a paycheck until at least then.

“To me, I’m still young,” he said. “But there are days when I’ve had enough and would like to partly retire.”

But Knapp worries that with several retirement-age colleagues in his lab, not everyone will qualify for part-time work.

“It’s just an unknown,” he said. “I’m interested to know, how the heck are they going to implement this thing and am I going to be eligible to apply?”