Washington's air defense system restricts private air traffic while providing only the illusion of security against a terrorist attack, leaders of a key House panel said yesterday.

Rep. John L. Mica (R-Fla.), chairman of the House Transportation and Infrastructure subcommittee on aviation, said the Federal Aviation Administration has identified fewer than half of the 2,400 flights that have improperly breached the restricted airspace over Washington since January 2003.

The Air Defense Identification Zone covers 3,000 square miles and requires pilots to identify their aircraft, activate identification beacons and stay in two-way radio contact with air controllers. Questions about its effectiveness were raised after a plane carrying Kentucky Gov. Ernie Fletcher (R) breached the no-fly zone June 9 and prompted the evacuation of the U.S. Capitol.

"I have to ask what benefit the ADIZ provides to aviation security," Mica said at yesterday's hearing, which drew officials from the FAA and the Transportation Security Administration.

Jonathan Fleming, chief operating officer for the TSA, said the agency would look into Mica's charge but noted that no flights have posed a threat. He said the agency has investigated all 30 violations of the no-fly zone, which extends about 16 miles around the capital. The D.C. Flight Restricted Zone, as it is known, bars most traffic except commercial flights to and from Reagan National Airport.

"I am unaware of flights into the flight restricted zone that are unidentified," Fleming said. TSA officials previously have reported successfully investigating more than 2,000 aircraft, and Fleming said no case has been linked to terrorism.

The FAA did not notify air defense authorities that Fletcher's plane had a broken transponder. Without an identifying signal, other radar displays showed a potentially menacing aircraft breaching the restricted zone on a day when security was high because of former president Ronald Reagan's funeral.

The FAA said it has eliminated a technical gap between air defense and FAA radar displays that led to the error, reaffirmed that all planes approaching Washington must have working transponders and is retraining personnel.

"On behalf of the FAA, I regret that our agency contributed to the events that led to the unnecessary evacuation of the U.S. Capitol," FAA Vice President Linda Schuessler said. "We don't believe it can happen again."

Rep. Peter A. DeFazio (D-Ore.) said that the no-fly zone does not appear to give ground-based air crews enough time to intercept an attacker and that Homeland Security aircraft are unarmed, except for helicopter crew members who carry submachine guns. He said the current system will "defend against innocent intrusions but not against actual determined terrorist intrusions."

Several House members, including Rep. James P. Moran Jr. (D-Va.) and Del. Eleanor Holmes Norton (D-D.C), called on the Bush administration to reopen National Airport to general aviation, shut off since the Sept. 11, 2001, terrorist attacks on New York City and Washington.

Secretary of Homeland Security Tom Ridge is reviewing a TSA plan to reintroduce general aviation. The decision, in consultation with the White House, national security officials and the Department of Transportation, is not expected before November.

Phil Boyer, president of the Aircraft Owners and Pilots Association, which represents more than 10,000 pilots at 19 public-use airports within restricted Washington airspace, said the system is "nothing more . . . than a great way to harass pilots."

Mica highlighted the plight of private pilots by releasing data showing that waivers have been granted to planes carrying 79 elected officials, among them members of Congress and governors.

The beneficiaries include former presidents George H.W. Bush, Bill Clinton and Gerald R. Ford; Florida Gov. Jeb Bush (R); the Democratic presidential and vice presidential candidates, Sens. John F. Kerry (Mass.) and John Edwards (N.C.); House Speaker J. Dennis Hastert (R-Ill.) ; and Senate Majority Leader Bill Frist (R-Tenn.).

"VIPs, members of Congress and other elected officials continue to receive special treatment under this process," said Mica, who called for an end to special waivers. "If the private sector is going to suffer, then so should everyone else."

The most frequent flyer, with 46 flights, was Virginia Gov. Mark R. Warner (D), who lives in Richmond and keeps a home in Old Town Alexandria.

Warner spokeswoman Ellen Qualls said the state had no say in how or why waivers are granted and that all flights involved state aircraft for official business. Warner supports restoring general aviation at National Airport.

"It's not surprising that the Virginia governor would be a top user of the Virginia airport closest to Washington," she said. "If he's traveling by plane, that's the closest airport to the District, when he's traveling on business."

House homeland security committee spokeswomen said the panel hopes to receive a military briefing on the June 9 incident with the House Armed Services Committee.

FAA Chief of Staff David M. Mandell and agency Vice President Linda Schuessler confer with advisers during a break in the hearing. Linda Schuessler, FAA vice president of systems operation, and Jonathan Fleming, TSA chief operating officer, testify on air security.