WASHINGTON — In a time of unparalleled aviation safety in the United States, reports of mistakes by air traffic controllers have nearly doubled — a seeming contradiction that puzzles safety experts.

The near collision last month of an American Airlines jet with 259 people aboard a

nd two Air Force transport planes southeast of New York City, coupled with the rise in known errors, has raised concerns in Congress that safety may be eroding.

A US Airways plane carrying 95 people crossed paths with a small cargo plane in September, coming within 50 to 100 feet of each other while taking off from Minneapolis. A few months earlier a US Airways Airbus 319 intersected the path of another cargo plane during an aborted landing in Anchorage, Alaska.

In fact, an air traffic controller at the Ronkonkoma, N.Y., radar facility that handled the American plane says he complained about a lax atmosphere at the facility — the second busiest of its kind in the nation.

Controller Evan Seeley, 26, said he ran afoul of the local union when he tried to prevent sick leave and scheduling abuses aimed at increasing overtime pay. Even more disturbing were Seeley’s charges that controllers sometimes watch movies and play with electronic devices during nighttime shifts when traffic is slower. He said he has sent his complaints to the Transportation Department’s inspector general and to the Office of Special Counsel, which investigates whistleblower charges. He claims his recent demotion from his position as a front-line manager was related to his attempts to correct problems.

Union officials called Seeley’s claims “wild” and “baseless.”

In the 12 months ending on Sept. 30, 2010, there were 1,889 operation errors — which usually means aircraft coming too close together, according to the Federal Aviation Administration. That was up from 947 such errors the year before and 1,008 the year before that. Before 2008 the FAA used a different counting method.

The FAA administrator says the higher number of known errors is due to better reporting and technology that can determine more precisely how close planes are in the air.

Very few of the errors fall into the most serious category, which could result in pilots taking evasive action to prevent an accident. But those instances have also increased. In the year ending Sept. 30, there were 44 such events; 37 in the prior year and 28 in the year before that.

The situation has sparked concern in Congress. FAA Administrator Randy Babbitt was repeatedly asked about the error increase and Seeley’s claims at a hearing before the House aviation subcommittee earlier this week.

“We don’t want to play ‘gotcha,'” Rep. Thomas Petri, R-Wis., the panel’s chairman, told Babbitt. “We do want, though, to have people know that we’re concerned and we’re watching.”

The FAA chief noted the dearth of major accidents. Saturday is to mark 24 months in which there have been no fatal airline accidents. The last was the crash of a regional airliner on Feb. 12, 2009, near Buffalo, N.Y., that killed 50 people.

“That record is hard bought and we’re very proud of it,” Babbitt said.

Babbitt said the rise in errors is because of a new safety program that protects controllers from punishment for mistakes they voluntarily report The program is aimed at increasing error reporting so trends can be spotted and new training methods, changes in procedures or other actions can be taken. It is modeled after a successful error-reporting program for airline pilots.

The program, which started in 2008 and was fully phased in last year, is receiving about 250 reports a week. But safety experts note that those reports generally aren’t counted in FAA’s official error tally and thus don’t explain the surge.

Bill Voss, president of the Flight Safety Foundation in Alexandria, Va., and a former controller, said there is reason to be concerned, but “how much to be concerned is difficult to determine because there are so many changes going on to sort out.”

“I know the FAA is paying close attention to controller errors right now,” Voss said. “The public face may be that they are ascribing it to the reporting system, but privately they are working very hard to improve the error rate at every level.”

Babbitt said he has tried to create a collaborative climate where controllers and other employees feel freer to acknowledge mistakes.

Former controllers give Babbitt high marks for his efforts. In the past, they said, controllers frequently tried to conceal errors in order to escape punishments that too often didn’t distinguish between minor infractions and truly dangerous behavior.

“Administrator Babbitt is attempting to change the culture from a blame culture to a learning culture,” said Sid McGuirk, who worked for 35 years as a controller, frontline manager, and error investigator.

The use of new, more precise aircraft tracking systems at a small number of the FAA’s 108 facilities has also picked up instances of planes flying too close together that would otherwise have gone unnoticed, Babbitt said. That has also contributed to the increase, he said.

Babbitt’s changes coincide with a period of rapid turnover in the controller work force. Many of today’s 15,500 controllers were hired in the years after President Ronald Reagan fired striking controllers in 1981 and are now eligible to retire. FAA has hired 7,000 controllers in the past five years and plans to hire 5,200 in the next five, according to the National Air Traffic Controllers’ Association. About a quarter of the work force is in training, which can take up to five years.

The FAA sent a special team to New York this week to investigate Seeley’s claims, which were first reported by the New York Post.

Seeley’s attorney sent the FAA a letter on Jan. 17 offering to not go public with the allegations if Seeley was reinstated as a manager and transferred to a Texas facility where he had previously worked. The request was refused.