One year after most of the country's air traffic controllers were fired for staging an illegal strike, the Reagan administration appears to have proved that it could keep airplanes flying safely and in large numbers without them.

Supervisors, controllers who stayed on the job, laid-off pilots and 2,300 new trainees are moving traffic at 83 percent of pre-strike levels, according to the Federal Aviation Administration. Safety studies have given the interim control system a generally clean bill of health.

But the hard-line response to the strike, which began a year ago today in defiance of the White House, has exacted a mammoth cost in financial and human terms.

Traffic restraints have created millions in new losses for U.S. airlines, which were already reeling from the recession, and triggered the layoffs of thousands of pilots, mechanics and other employes. Departure delays have become a way of life at many big airports.

Countless families and friendships have been torn apart by layoffs, firings and picket-line tension. The Professional Air Traffic Controllers Organization, which led the strike, has been bankrupted, stripped of its authority to bargain and forced to trundle its files into packing boxes.

And though traffic seems to be moving smoothly for the present, there is concern in Congress and the aviation industry that traffic will remain restricted much longer than the FAA predicts. There is also fear that six-day work weeks and postponed vacations are eroding morale and alertness of working controllers and that serious labor-management friction remains.

Administration officials discount the criticism, arguing that full capacity will return late in 1983 and personnel problems are being corrected. "We wanted to avoid the strike," said Transportation Secretary Drew Lewis. But since it happened anyway, he and other officials say, the administration will finish the job it started.

Coping with the walkout was complicated by the fact that the union, PATCO, was strongest where air traffic was densest--the New York and Chicago areas, in particular. Facilities there were hit the hardest.

"When I came here on Aug. 3, I expected to see 167 people" for the a.m. shift, said Doug French, acting chief of the Chicago enroute center, which controls the skies over 120,000 square miles in the Midwest and Great Lakes area. "Seventeen showed up."

Altogether, Chicago center fired 457 of its 600 controllers. Nationwide, 11,400 of the FAA's 17,400 controllers lost their high-paying jobs after ignoring a 48-hour deadline to return. "The union was much more solid than we anticipated," says Lewis, who directed much of the administration's response to the strike.

Chicago center's response to the strike mirrored methods used to keep the nation's 500 airport towers and the other 19 "enroute" centers operational with only a fraction of the former staff.

Supervisors were put to work at the screens. Six-day weeks became the rule at the facility, located in Aurora, one hour's drive from Chicago. Nonstriking controllers from lesser hit centers were brought in, and unemployed pilots hired to do backup work in the control room. At airport towers, meanwhile, staffing was bolstered by military controllers.

At the same time, traffic was reduced on orders from the FAA and morning and evening peaks spaced more evenly. The FAA's "Central Flow" command center in Washington watched traffic nationwide and ordered airlines to hold planes on the ground if an overload threatened.

The smaller staff worked harder, officials say: in Chicago, six hours of actual control work became standard opposed to the old four hours. "The overall system is much more efficient," said French.

Chicago's workload was further reduced by farming out airspace to adjacent, less-affected centers (Cleveland center took command of airways to the east above 24,000 thousand feet) and tying airport towers, like Grand Rapids and Muskegon, together to give low level, short distance enroute control. (The strike generally hit towers less hard than enroute centers.)

Gradually, Chicago center's traffic, cut to half the usual load of 6,800 planes in the strike's first days, inched back to about 5,500 today.

For the airlines, the first days were chaotic. The FAA restricted access to 23 major airports, forcing cancellation of thousands of flights. Those that did go often took excruciating 60- and 90-minute delays at the gate. Canadian controllers staged a sympathy action, tying up cross-border traffic for several days.

Controllers also had trouble with pilots who, intentionally or out of ignorance of the new rules, entered the control system when they shouldn't have. One way was to take off under Visual Flight Rules, without ground control, then to radio controllers and tell them instrument guidance was needed.

But as time passed, order returned and airlines and travelers began to see the strike was not the catastrophe they had feared. It was possible to get from place to place, though not necessarily on time. Frequent travelers learned to allow for extra time in the departure lounge.

Delays persist at major airports, though they have fallen off considerably since the strike. In June this year, according to FAA figures, 38.8 flights per 1,000 landings and takeoffs at 16 of the restricted airports were 15 minutes or more late. In June 1981, before the strike, the figure was 27.5. Figures at individual airports can be far higher, however.

Another strike drawback for travelers is that with jets flying with fuller loads, overbooking and bumping have risen. According to the Civil Aeronautics Board, 15,141 people were involuntarily denied confirmed seats on flights in December 1981, for example, compared to 12,495 the previous December, an increase of 21 percent.

The strike hurt the airlines, industry specialists say, but not as much as the recession, which was already biting deep into air travel. "We had already laid off thousands of people in the year preceding the strike," said William Jackman, spokesman for the Air Transport Association, which represents 30 major airlines.

Airlines cut their losses after Aug. 3 by dropping their most unprofitable routes, flying their wide-bodied planes more often to move more people with fewer flights, and developing business at non-restricted airports. Costs were cut by the layoff of close to 15,000 people and lower consumption of fuel.

The strike would have hurt much more had it come in a time of expanding air travel. But coming on a downturn, when planes were already empty, it in effect helped airlines make cuts that should have been made anyway. It is not possible to separate strike from recession losses, but in the past year, ATA estimates, members lost close to $1 billion on sales of about $35 billion. They broke even in the year before.

Impact on individual airlines depended largely on where they had their major operations. Those depending on New York and Chicago, PATCO strongholds, were hard hit. But airlines serving areas where PATCO was weaker, the Southwest for instance, found operations affected hardly at all.

Carriers discovered that one side effect of the strike measures was that the industry was effectively reregulated, reversing trends that began in 1978. Suddenly the federal government was back in the business of telling people where they could and couldn't fly. Secretary Lewis has been on the phone with airline presidents constantly since the strike began. "Every airline wants to get a little bigger slice of the pie," he said.

Airlines quickly learned that although total flights were restricted, they could expand their flights if their competitors fell off. By this March, some were operating more planes at restricted airports than they did in March 1981, before the strike.

According to a Civil Aeronautics Board study, American was up in departures by 5 percent, New York Air 86 percent and Continental 16 percent. The hardest hit airlines, in terms of departures, were Pan American, down 31 percent, Eastern 14 percent, and Trans World 17 percent.

Despite its losses, the industry has backed the administration stand against the strikers. Airline executives say safety and efficiency will be best served by replacing the strikers. But in addition, airlines must remain on good terms with the FAA.

Secretary Lewis declares flatly that "the airways are safer now than they were pre-strike." Major aviation associations, including the Air Line Pilots Association, have echoed that view. Traffic is lighter and the planes spaced farther apart in the air, they say, and long-standing antagonism between pilots and controllers over who commands the plane has diminished.

Major safety studies to date have also concluded the system is safe, while raising concern that overwork could change that. The National Transportation Safety Board, for instance, examined in detail the two months of operations after the strike and found that the system "was operated safely" in that period.

However, the board has ruled that the mid-air collision of a helicopter and light plane over the New Jersey Meadowlands sports complex last September, in which two people were killed, was caused in part because the controller was tied up by a "non-essential administrative telephone call" shortly before the accident.

FAA figures show that reports of "operational errors," or two airplanes having less than legal separation, and "near misses" have dropped since the strike. However, these figures rely heavily on calls from pilots and working controllers and questions remain whether those people may be less eager to report them than in the past.

Members of PATCO and some other aviation specialists, however, continue to argue that it is impossible to fire so many people in a highly technical field without affecting standards.

"There's less experience in the towers," says Matthew Finucane of the Aviation Consumer Action Project, a Ralph Nader organization. " . . . It's taking a system with a lot of built-in margins of safety and reducing the margins."

Concern continues that fatigue is mounting among the working controllers and could affect performance. The House Post Office and Civil Service Committee, for instance, noted in a May report that one working controller had remarked "the glory is fading" and said a team supervisor at Chicago O'Hare had averaged 68-hour work weeks in February.

The FAA, however, says that morale and standards remain high and that work weeks are coming down at many facilities as new trainees arrive. Facility chiefs have been ordered to give everyone at least one full week of vacation this summer, FAA air traffic control chief Ray Van Vuren said.

FAA projections for restaffing the system have generated some skepticism in the industry and Congress, too. So far, 2,300 people have completed training at the controllers academy in Oklahoma City and are now in on-the-job training. Lewis has said that as more graduate, the last strike-related restrictions will be lifted by the end of 1983.

But Post Office and Civil Service Committee Chairman William Ford (D-Mich.) argues that "it'll be 1984 sometime at best." The only way to restore capacity quickly, he said, is to draw on what his committee calls "the existing talent pool"--fired controllers. The committee has reported out a bill that would allow, but not require, the FAA to rehire selectively. That has created a deadlock with the White House, which opposes any suggestion that strikers be rehired.

In the aviation industry, meanwhile, there is also concern that the FAA will limit peak-hour traffic indefinitely. Doing so is a much more efficient use of FAA resources and eliminates the need for big peak-hour staffing. Secretary Lewis denies that this is planned: "That is positively wrong," he said.

There is also concern that conflicts between managers and controllers could recreate the strike. Van Vuren says that numerous human relations programs already have been implemented in the past year to address these problems. The House bill also requires a special committee to advise on personnel relations.

Meanwhile, the FAA is not simply rebuilding the old control system. PATCO's strike proved that the facilities were vastly overstaffed, Lewis has said, and current plans are to replace only about 7,800 of the 11,400 people fired.