WASHINGTON -- The government will lose about $200 million a week in airline ticket taxes and $2.5 billion in airport construction projects will come to a halt if the Federal Aviation Administration is forced to shut down, Transportation Secretary Ray LaHood said Thursday.

A shutdown looks increasingly likely because Congress hasn't been able to come to an agreement on legislation to extend the FAA's operating authority, which expires at midnight tonight.

If that happens, airlines would no longer collect federal ticket taxes. About 4,000 FAA workers whose jobs are funded with ticket tax revenues will be furloughed, LaHood told reporters at a news conference.

"This is no way to run the best aviation system in the world," LaHood said. "Congress needs to do its work."

Long-term authority for the FAA expired in 2007. Unable to agree on long-term funding legislation for the agency, Congress has kept the FAA operating through a series of 20 short-term extension bills.

Previous extensions have been routine. But this time House Republicans added a provision to what would be the 21st extension eliminating government subsidies for airline service to 13 rural communities. Senate Democrats say the provision is unacceptable, but House Republicans have been unwilling to remove it.

Initially, the largest furlough would involve nearly 1,000 workers at FAA headquarters in Washington, transportation officials said. Another 647 workers at FAA's technology and research center in Atlantic City, N.J., and 124 workers at the agency's training center Oklahoma City would also be furloughed.

Air traffic controllers, considered essential safety personnel, would remain on the job.

LaHood refused to answer questions about the potential consequences if a shutdown were to continue for more than a few days.

Sen. Jay Rockefeller, D-W.Va., chairman of the Senate committee that oversees the FAA, said that if a shutdown were to continue through mid-August, funds to support air traffic control operations would diminish to the point where the FAA would have to close those operations at smaller airports in order to concentrate its resources at busier facilities.

The situation could be a financial boon for airline passengers. Barring an agreement, the taxes will disappear from airline and ticket- selling websites at midnight today.

The federal tax on a $300 round-trip airfare is about $61, according to the Air Transport Association. Airlines would still collect airport fees.