ASHINGTON, Sept. 20 — Transportation Secretary Norman Y. Mineta said today that his department knew elements of the threat to aviation before last week's terrorist attacks but could not have pieced them together to avert the plot.
In his first appearance before Congress since hijackers seized four jetliners and used them to kill more than 5,000 people, Mr. Mineta did not elaborate on what officials knew in advance, but he said that no one under his jurisdiction was at fault.
Members of the House and Senate agreed and warmly praised Mr. Minetta, who had served in the House from California for 21 years. They did not press him to elaborate and seemed more prone to blame the intelligence agencies for any responsibility the government must bear.
And they seemed most interested in getting the flying public back in the air, urging Mr. Mineta and his deputy, Jane Garvey, the head of the Federal Aviation Administration, to reopen Ronald Reagan National Airport, across the Potomac from Washington, the only major airport in the country still closed.
Mr. Mineta said that since the attack, officials had studied "whether or not there was a matrix we could build," but that in hindsight, he did not see how they could have discovered the hijackings before they occurred. Ms. Garvey said the whole security system was geared for explosives, not knives.
The attack, she said, had "changed the way we think, and challenged every assumption," because before that day, no one had successfully seized a commercial jet as a weapon. (The closest anyone came was a disgruntled FedEx employee riding in a FedEx cargo plane's cockpit who attacked the pilots with a hammer in 1994 and intended to crash the plane, but was thwarted.)
Despite extensive testimony from the Transportation Department's inspector general and a specialist from the General Accounting Office about a long history of failings in security — all of them documented over the years in reports to Congress — lawmakers said the nation was vulnerable because of lapses by intelligence agencies, whose representatives were not at the hearing.
"We could not expect an $8-an- hour security screener to foil an attack that a multibillion-dollar intelligence system could not prevent," said Senator Patty Murray, Democrat of Washington.
Mr. Mineta and Ms. Garvey testified before the Senate Commerce Committee and then in an unusual joint meeting of the House and Senate Transportation Appropriations Committees.
Each panel seemed most interested in returning aviation to normal levels of patronage. The number of commercial planes flying is nearly 80 percent of normal, but passenger loads are off by more than half.
Senator Barbara Boxer, Democrat of California, said, "We are not going to get back on our feet unless people get back on the planes."
Mr. Mineta said he and Ms. Garvey were considering a "whistle-stop tour" by plane, holding news conferences at the airports to urge people to return to the skies.
When the two officials came under pressure to reopen Ronald Reagan National Airport, Mr. Mineta said that decision was not in his hands.
Senator Ernest F. Hollings, Democrat of South Carolina and chairman of the Commerce Committee, noted that the airport's closing was a particular problem for US Airways, which has a hub there and was in economic trouble before the hijackings. He then said, "While I'm palavering and dillying, I'm putting them out of business."
Mr. Mineta answered, "It's in the hands of the National Security Council and the Secret Service."
Senator Hollings retorted: "If it's in the Secret Service's hands, it'll never get open."
Mr. Mineta said those agencies wanted planes to approach the airport only from the south, and leave in that direction, too, so they would not fly over the Pentagon. That would mean the airport could operate only when there was hardly any wind, he said.
Another point of debate was over whether the federal government should take over operation of the 700 passenger screening checkpoints around the country. Mr. Mineta said that would require 28,000 people and an annual budget of around $1.8 billion; he said that the government would have to assure that a better job was done, but he said that the White House had not concluded that the government should do it.
Members of Congress also called for improvements in cockpit doors and other safety measures on planes, but got disappointing responses from expert witnesses. Capt. Duane Woerth, president of the Air Line Pilots Association and a member of a task force on cockpit security appointed by Mr. Mineta, was asked about arming cockpit crews and replied, "We can't be Sky King and Wyatt Earp at the same time."
"If we're already to the point that the bad guy is on the airplane, we've failed most of the systems to that point," Mr. Woerth said, calling for armed air marshals instead.