The Federal Aviation Administration said yesterday that it has 81 fully qualified air traffic controllers working at Chicago's O'Hare International Airport. A Wednesday article on air traffic control problems at O'Hare reported a lower number. Federal Aviation Administration officials told a House investigations subcommittee Thursday that 52 fully qualified air-traffic controllers work at Chicago's O'Hare International Airport, a figure included in a Washington Post article July 24 about controller errors there. The next day, after the FAA insisted that the number is 81, The Post published a correction but sought further documentation. In response to that and an independent inquiry by subcommittee member Guy V. Molinari (R-N.Y.), the FAA has confirmed that the 81 include a total of 29 supervisors handling air traffic and controllers fully qualified for only two of the three jobs performed by O'Hare controllers.

An unusually high number of near collisions at Chicago's O'Hare International Airport has spurred a National Transportation Safety Board investigation.

Board specialists, who recently returned from O'Hare, are so concerned that they are considering a formal recommendation to restrict flights at the world's busiest airport until more Federal Aviation Administration controllers become available, sources said. So far this year, there have been 14 close calls at O'Hare, only two of which have been publicized. Most of the incidents involve controller errors, the sources said.

"There are just too many planes there right now," one source said. June traffic at O'Hare set a record and was 26 percent higher than in June 1985. The FAA has only 52 fully qualified air traffic controllers in the O'Hare tower, although the authorized strength is 94. In addition, several trainees have authority to direct airplanes in limited blocks of airspace before completing their instruction.

FAA Administrator Donald D. Engen said in an interview Tuesday:

"If anything, what's going on out there is that increased volume has increased the controller infractions, and that's probably a direct-line relationship . . . . Chicago O'Hare is nothing more than a very busy airport. It's not in a state of disrepair . . . . We're dealing with that. I'm not concerned that we have a big problem at O'Hare."

The problems at O'Hare come amid increasing concern on Capitol Hill that the FAA is not rebuilding the air traffic control system quickly enough after a controllers' strike five years ago.

Rep. Guy V. Molinari (R-N.Y.), who has been especially critical of the FAA, has significant support for rehiring some of the 11,400 controllers fired by President Reagan. The House will vote on that as an amendment to a transportation appropriations bill that could reach the floor today.

The sources said the 14 incidents, known in FAA jargon as "operational errors," are far more than usually occur in six-month periods at O'Hare or similarly busy airports, including those at New York, Los Angeles and Atlanta.

In the most recent unpublicized incident, a Western Airlines jet was directed to take off July 2 on a northwest runway, then turn west. A United Air Lines jet was directed to take off on a westbound runway and turn slightly north. Visibility was severely limited by fog and clouds.

The planes received their instructions from different controllers, who did not coordinate the takeoffs. As the jetliners headed toward each other, they were picked up on radar in the darkened room beneath the O'Hare tower and a computerized "conflict alert" warned a controller.

"The controller really had to pry 'em apart" with hastily radioed instructions, a source said. The official estimate was that the two planes were converging and came as close as a half mile horizontally and 400 feet vertically. FAA regulations require a minimum of three miles and 1,000 feet.

In another recent incident, United and Air Wisconsin jets came within a mile of each other after taking off.

In May, there were two near collisions on the runways at O'Hare, prompting the safety board to recommend that two coordinators be added to assist controllers. One was added.