WASHINGTON - The Federal Aviation Administration is experiencing substantial delays and cost overruns in a key component of its effort to modernize the U.S. system for air-traffic control, an inspector general's report said Thursday.

The inspector general, Calvin L. Scovel, is concerned with a computer program that manages planes at high altitudes. The program is critical in the FAA's more long-term move to GPS technology for tracking airplanes. The current system relies on World War II-era radar technology.

Scovel said in a letter to lawmakers that more than 200 problems were found with the program, prompting a temporary halt to further testing. Although the FAA has resumed testing and says progress is being made, updated software has exhibited new problems and old ones.

The computer woes will force the FAA to maintain aging equipment longer than planned and retrain air-traffic controllers. Scovel said it was disconcerting that the system passed testing and that the FAA assumed control and responsibility for it, despite the shortcomings.

The FAA told investigators that many of the problems encountered could only be identified in a live environment.

The FAA estimates it will need to spend $200 million for the program this fiscal year - about $70 million more than projected. It will take $500 million more and from three to six years to complete that particular aspect of the modernization program, which is referred to as NextGen, Scovel said.

The NextGen program should improve the efficiency of the National Airspace System and improve the environment by reducing the amount of fuel that planes burn.

In 2009, a task force made up of government and industry officials issued 34 recommendations on steps needed for putting the new tracking system in place, but the inspector general said the FAA lacks a detailed implementation strategy.

Two Republican lawmakers, Reps. John Mica of Florida and Thomas Petri of Wisconsin, issued a news release on Thursday promising vigorous oversight of the FAA's work.

"FAA needs to tighten up its oversight of this critical and costly modernization program," said Mica, the incoming chairman of the House Committee on Transportation and Infrastructure.