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 has safety experts puzzled.

The latest incident — the near midair collision of an American Airlines jet with 259 people aboard and two Air Force transport planes southeast of New York City, has raised eyebrows in Congress and led to questions about a nonpunitive culture of error reporting in air-traffic control facilities.

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 frontline manager was related to the complaints.

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’s official tally. During the same period a year earlier, there were 947 errors. And the year before that there 1008 errors. Before 2008 the FAA used a different counting method, so a more historical pattern isn’t available.

The FAA administrator says the higher number of reported errors is due to better reporting and better 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.’ We do want, though, to have people know that we’re concerned and we’re watching,” Rep. Thomas Petri, R-Wis., the panel’s chairman, told Babbitt. Petri said he may hold a hearing on the issue.

The FAA chief noted the dearth of major accidents. This Saturday will mark 24 months in a row 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 the number of errors is because of a new safety program that protects controllers from punishment for errors 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.”

Asked about this inconsistency, Babbitt said he has tried in general to create a collaborative climate where controllers and other employees feel freer to acknowledge mistakes.

The controllers’ union has called Seeley’s allegations “wild” and “baseless.” The FAA sent a special team to New York this week to investigate his claims, which were first reported by the New York Post.