The Federal Aviation Administration estimates that about half of its air traffic controllers, nearly 7,100, could retire over the next nine years.

The retirement surge means that the FAA will need to begin hiring and training controllers at levels not seen since President Ronald Reagan fired striking controllers in 1981.

"It's substantial, it's inevitable and it's imminent," JayEtta Z. Hecker, a director at the General Accounting Office, testified last week at a House hearing.

The big question is whether the FAA can replace that many controllers that fast.

Marion C. Blakey, the FAA administrator, said she will have a plan to deal with the projected retirements ready by December. That plan will heavily influence the FAA's budget request for fiscal 2006, she indicated.

Blakey, however, is going to need more than a plan.

She is going to need money from Rep. Ernest J. Istook Jr. (R-Okla.) and Sen. Richard C. Shelby (R-Ala.), chairmen of the Appropriations subcommittees that determine the FAA's annual budgets.

She is going to need support from the Office of Management and Budget, especially Joshua B. Bolten, the president's budget chief, and from Clay Johnson III, the president's adviser on federal management issues, and from the Office of Personnel Management, led by Kay Coles James.

Perhaps just as important, Blakey is going to need good advice from John Carr, Ruth E. Marlin and other leaders of the National Air Traffic Controllers Association, the union that represents the controllers and some other FAA employees.

Without a concerted effort, the FAA risks not having the right controllers in the right towers at the right time. By most accounts, the retirement wave will hit the FAA at a time when its workload will be increasing as air travel rebounds from the effects of the Sept. 11, 2001, terrorist attacks.

"Because it takes years to train and gain the experience and skills needed to be a proficient controller, we must act now to keep our air traffic control system from being crippled in the near future," Rep. John L. Mica (R-Fla.), who convened last week's hearing as chairman of the House aviation subcommittee, said in a statement.

Creating a new staffing model for the FAA will not be easy. In recent years, according to the GAO, the FAA typically has hired only after a controller leaves. This one-for-one approach essentially ignores replacement training time, generally two to four years, and sometimes longer, depending on the tower or center.

In the future, the FAA needs to develop better data on retirement and turnover at its facilities, do a better job of assessing the skills of controllers before assigning them to towers, and reduce the time and cost of training, Alexis M. Stefani, principal assistant inspector general at the Transportation Department, testified at the hearing.

Because so much controller training is on the job, the FAA needs to staff up for what the GAO calls an "overlap period" -- when an experienced controller expected to retire soon and a newly hired controller are able to work side by side.

It doesn't help that Congress has long been skeptical of the FAA's management abilities. That skepticism was probably reinforced by recent findings that FAA headquarters stumbled badly in responding to the 9/11 hijackings.

Congress last year did not provide money to hire an additional 328 controllers that the FAA requested. Now, the Bush administration has opted not to seek funding in fiscal 2005 to hire additional controllers to address the retirement wave.

Despite its muddled budget outlook, the FAA hired 762 controllers late last year and some are in the training pipeline. Through May, the agency has hired one controller. Meanwhile, about 400 controllers have left since the 762 were hired.

The rate of hiring, however, has to pick up. Estimates show that the FAA needs to replace 2,180 controllers between now and 2007 and that it will need an additional 2,000 controllers by 2010 to address increases in air travel.

The FAA also is at risk of losing its most experienced hands as it ramps up hiring. About 93 percent of the FAA's 1,862 controller supervisors will be eligible to retire by the end of 2011, according to the GAO.

"The FAA is not preparing to maintain the air traffic system," Marlin said. "In fact, you are setting up a situation where the system could collapse under its own weight."