Air traffic controllers will be guaranteed a minimum of at least nine hours off between tightly scheduled shifts under a plan announced by federal officials Sunday morning.

“We expect controllers to come to work rested and ready to work and take personal responsibility for safety in the control towers,” said U.S. Secretary of Transportation Ray LaHood. “We have zero tolerance for sleeping on the job.”

The Federal Aviation Administration said the new rules were already in place, although it may be the end of the week before they take full effect.

“Research shows us that giving people the chance for even an additional one hour of rest during critical periods in a schedule can improve work performance and reduce the potential for fatigue,” said FAA Administration Randy Babbitt.

The announcement by LaHood and Babbitt comes a day after a seventh air traffic controller was suspended for sleeping on the job. The incident in a Miami traffic center prompted Babbitt to announce immediate changes in scheduling practices deemed to put drowsy controllers behind the microphone.

Finalizing those schedule changes took negotiation with the controllers union, the National Air Traffic Controllers Association, whose members favor scheduling practices that compress their schedule and lengthen their weekends to three days or more.

Those issues were worked out yesterday, according to an internal union e-mail sent to members late Saturday night.

The changes include a guaranteed nine-hour minimum between shifts, a ban on trading shifts with other controllers unless the minimum is met, prohibited swapping of regular days off in some circumstances and an extension of the hours a manager is on duty until 1 a.m.

LaHood said on “Fox News Sunday” that the flying public needs to be assured that the nation’s aviation system is safe. He said he flies “commercially all the time” and wakes up thinking about transportation safety.

“I’m really mad about it,” LaHood. “We’re going to work 24/7 to make sure these controllers are well trained and alert.”

The union explanation to its members Saturday night indicated that controllers would be allowed to nap while on their scheduled breaks, a practice that had been prohibited because controllers are subject to being summoned to return early if airplane traffic demands.

“While we are working to also change FAA policy on rest periods on breaks we have been told that they will not discipline anybody for using their break time to ensure that they are alert while on position,” the memo said. “We expect more formalization around recuperative breaks to occur soon.”

The union also said it expects that radios and CD players, but not use of headsets, will be permitted on overnight shifts in control towers and in radar rooms during other shifts. They had been banned.

The sleeping controllers have been working the overnight shift, and until their dozing was discovered, at least 28 control facilities had just one controller working that shift. Babbitt and LaHood ordered an end to single-person staffing this week.

Although scheduling is flexible to meet the air traffic system’s demands, one of the most popular schedules is known as the 2-2-1. Under it, a controller begins the workweek with two evening shifts, does a quick turnaround to a pair of day shifts and then does another quick turn before an overnight shift.

Those quick turnarounds — usually just eight hours — have been blamed for controller fatigue.

The 2-2-1 is favored by many controllers because it compacts their workweek and creates a weekend of at least three days. That schedule format would be altered to extend the number of hours off under the new plan, but it would not be fundamentally changed, according to the union memo.

In 2007, the National Transportation Safety Board recommended that the FAA work with the National Air Traffic Controllers Association to “reduce the potential for controller fatigue by revising controller work-scheduling policies.”

Babbitt, who has developed a close working relationship with Paul Rinaldi, president of the air traffic controllers union, worked on the scheduling changes with Rinaldi’s group on Saturday. The changes will affect 15,475 controllers.

Babbitt and Rinaldi are scheduled to begin visiting air traffic control centers on Monday to talk with controllers about the recent problems and expected standards of conduct. The FAA also plans to implement a fatigue education program for controllers.

On Wednesday Hank Krakowski, the head of the FAA’s Air Traffic Control Organization, was forced to resign after recent embarrassments when controllers were caught sleeping and a year in which recorded errors by controllers — some of them leading to near mid-air collisions — increased 51 percent.