Sen. Dick Durbin called Wednesday for a federal investigation into the work conditions of Chicago-area air traffic controllers, including whether there are enough controllers to ensure runway safety.

"Controllers in the Chicago area are retiring at increasing rates and it is clear that the FAA does not have a plan for the future," the Illinois lawmaker said in a statement.

Durbin's request comes a week after the General Accountability Office released a study showing that O'Hare International Airport had the second-highest number of near-collisions on runways between 2001 and 2006.

Controllers in the Chicago region and elsewhere say they are weary and more error-prone after having to work repeated six-day weeks due to staffing level changes. The Federal Aviation Administration has said that staffing levels are adequate despite controllers' complaints.

Durbin's request -- in a letter to Calvin Scovel, inspector general of the Department of Transportation -- came after the senator met with Robert Sturgell, President Bush's pick to head the FAA.

FAA spokeswoman Tammy Jones said the agency would welcome an outside review of the controllers' situation.

"Air traffic controllers play a key role in managing safety on the airport surface," she said in a statement. "That is why we hired more than 1,800 air traffic controllers last year and will continue to hire thousands of new controllers over the next decade."

She added that the FAA limits the hours they can work in any given day and week to minimize fatigue.

A message left with the inspector general's office was not immediately returned Wednesday.

In 2006, the National Traffic Safety Board said in a letter to the FAA that insufficient sleep may have been responsible for controllers' lapses in judgment that led to two close calls on O'Hare runways.

In Chicago, there were 13 runway incursions during the 2007 fiscal year -- all but one at O'Hare, officials said after unveiling last week's report. Only two were considered serious.

The GAO report, requested by the House Transportation Committee's aviation subcommittee chairman, Rep. Jerry Costello, D-Ill., cited air traffic controller fatigue as a key factor affecting runway safety.

Durbin said he wants the DOT inspector general Scovel to immediately investigate air traffic tower facilities at Chicago, Aurora and Elgin, in northeastern Illinois, with special attention to staffing levels and fatigue.

"It's time to go into these facilities, start asking tough questions and do everything in our power to make air traffic safer," Durbin said.

Last month, an air traffic controller from the FAA's Chicago Center radar facility in Aurora mistakenly directed a passenger plane to descend in the path of a jet heading to O'Hare. Those planes came within seconds of a mid-air collision over Indiana.

The next week, two small private planes veered dangerously close to each other over Wisconsin because of miscommunication between air traffic controllers in Chicago and Madison, Wis., officials said.

Joseph Bellino, president of the O'Hare affiliate of the National Air Traffic Controllers Association, welcomed Durbin's move .

"It doesn't take a rocket scientist to know they have not staffed our facilities," he said. "They haven't done anything to improve facilities till recently, with hiring some college students who won't be ready for two years."

O'Hare had 57 controllers certified to work on their own, individually, as recently as 18 months ago, he said, but the number is now down to 41.

According to Durbin, the O'Hare tower is operating with 53.5 percent of the staff agreed to in 1998 by the controllers' union and the FAA. He said the Elgin facility is at 74 percent and Aurora facility is at its lowest staffing level in 14 years, with over 100 certified controllers ready to retire soon.