The restricted airspace over the nation's capital for private planes will expand beginning Monday in conjunction with the increase in the national terror threat level to orange, the Federal Aviation Administration announced Saturday.

"Terrorists are known to favor targets in the transportation sector and to consider our civil aviation system an arsenal of improvised weapons," said James M. Loy, undersecretary of the Transportation Department and head of the Transportation Security Administration.

"The Washington capital region is home to a number of particularly symbolic targets which must be protected. We appreciate the cooperation of the general aviation community as we implement sound security measures and tighten our defenses during this period of heightened alert," Loy said in a statement.

General aviation refers to privately operated aircraft, as opposed to airliners or military planes.

The new airspace control measures create what the FAA, an agency of the Transportation Department, calls an Air Defense Identification Zone in the airspace under 18,000 feet in roughly a 30-mile radius around Washington.

The previous restricted area was roughly 15 miles in radius.

Agency officials said they had designed the restrictions to increase security while allowing local general aviation airports to remain in operation.

The announcement said a text of the FAA order and a detailed map of the affected area would be provided to Flight Service Stations over the weekend and would be posted on the FAA Web site, www.faa.gov.

"As pilots in the National Capital Region know all too well, proper preflight planning requires them to check for and review Notices to Airmen prior to every flight," said FAA Administrator Marion C. Blakey.

"As all federal, local and state agencies work together to respond to an increased threat level, the FAA will redouble its efforts to get the pilot community timely, accurate information and to balance current security needs with the needs of the flying public."

The new measures, which become effective at 6 a.m. Monday, require general aviation pilots to maintain two-way radio communications, use a transponder and discrete beacon code, file IFR/VFR flight plans and follow standard air traffic procedures before entering the restricted zone.

All existing waivers in the Flight Restricted Zone have been canceled, but will be re-evaluated and reissued by the TSA, as appropriate, the announcement said.

The TSA also is enacting additional security measures for U.S. aircraft operators, U.S. airports and international departures from the United States and coordinating with the FAA to ensure that appropriate flight restrictions are in place.

The TSA requires increased inspections and surveillance of airport terminals and perimeters and areas controlled by aircraft operators as well as the posting of a law enforcement officer at all high traffic areas.

Vehicle restrictions also have been implemented. Additionally, TSA said it is working with local law enforcement to increase security at general aviation fields in the Washington region.