Air-traffic controllers are leaving their jobs at the fastest rate since President Reagan fired more than 12,000 striking controllers 27 years ago, spurring a rancorous debate over the safety of commercial aviation.

In recent months, fully certified controllers have been retiring in droves. Some of this was expected since many controllers hired after the 1981 air-traffic controller strike are becoming eligible to retire. But the retirement surge has accelerated beyond the Federal Aviation Administration’s projections because of a bitter labor feud that has dragged on since 2006.

In January, there were roughly 11,000 fully certified controllers, marking the lowest level in more than a decade. In September 2002, the FAA employed 12,801 fully certified controllers.

The National Air Traffic Controllers Association, which represents the FAA’s work force of roughly 15,, has declared staffing emergencies at high-intensity facilities in Atlanta, Chicago, Dallas, New York and Southern California. It calls the loss of so many veteran controllers a “growing crisis” amid surging traffic volumes and a big, hidden factor behind the persistent delays plaguing air travel.

The FAA acknowledges that shortages in the control tower can cause delays, but that it happens infrequently. To stabilize the situation, the agency is hiring hundreds of trainees and offering bonuses of as much as $24,000 to retain wavering controllers. But the pace of departures is leaving fewer experienced eyes to watch over the skies.

The Department of Transportation has reported that airline on-time rates plunged in December, leaving 2007 as the second-worst year for delays on record. (The worst occurring in 2000.) Flights operated by the largest U.S. carriers arrived on-time only 64.3 percent of the time in December, down sharply from an 80 percent rate in November. It was 70.8 percent in December 2006. For 2007 as a whole, the on-time arrival rate was 73.4 percent, down from 75.4 percent in 2006.

There are no solid numbers that show how much staffing issues contribute to delays, and the biggest causes of delays are adverse weather conditions and airline missteps, officials say. Yet entry logs on FAA operations provided by the controllers’ union show the impact of short-staffed facilities on arrival times.

NATCA president, Patrick Forrey, says as much as 25 percent of delays can be attributed to shortages. Some current and former controllers said personnel cuts often leave them alone at control stations, relying more on computers, where they used to work with human partners.

“Air-traffic control is all about climbing, bobbing and weaving. ... You have to push it to get everybody where they’re going on time,” said Jon Ramsden, a 50-year-old controller who retired in October after 25 years on the job. “The less people you have, the less you’re going to push it.”

Union officials also contend the shortage of fully trained controllers — those who have been trained to perform all the major control functions — is increasing the odds that a fatigued controller working overtime will make a catastrophic mistake.

“It’s amazing that it hasn’t happened so far,” Ramsden said. “The staffing issue has a direct impact on the safety of the public. It has to.”

The FAA says that despite the reduction in air-traffic controllers, air travel has never been safer. “There is nothing that we’re seeing at this point in time that gives us any concern,” FAA operations chief Hank Krakowski said.

So far, the air-traffic system has managed to avoid a catastrophic accident despite the shortage of fully trained hands. No major controller-caused jetliner collisions occurred in the 1980s — the last time staffing was a big issue and safety alarms were sounded — and none has occurred since a fatal accident was attributed to the control tower in Los Angeles in 1991.

Ramsden, the retired controller, traces his decision to leave back to September 2006, when the FAA imposed contract terms on the union after negotiators failed to reach a deal on pay and working conditions. The FAA ended up imposing significant pay cuts for new controllers and froze salaries of others, along with setting new work rules.

The labor impasse is also a factor stalling legislation that would jump-start the rollout of a new satellite-based navigation system touted by the FAA, airlines and many aviation experts as the best cure for the congestion and delays.

“Because of the bad blood between [them], it is having an impact that goes far beyond the day-to-day operations,” said Democratic Rep. Jerry Costello, of Illinois, chairman of the House subcommittee that oversees aviation.