BOSTON, Sept. 12 — While it is illegal to carry cans of hairspray, sparklers and rat poison onto passenger jets, Federal Aviation Administration regulations have for many years allowed passengers to carry knives with blades up to four inches long on commercial flights.

That changed today, as the agency announced new, far stricter security guidelines for airports nationwide. The measures were part of the first broad regulatory response to the hijackings Tuesday by terrorists, at least some of whom wielded knives and box cutters.

Airports were closed for a second day today. The F.A.A. said that once flights resumed, knives and cutting instruments of any size, made of metal, plastic or any other material, would no longer be allowed on commercial planes. They also cannot be used or sold in any part of airport terminals, including by diners in restaurants and concession stands.

Essentially, the new rules mean that airport diners will be left with forks and spoons, or possibly chopsticks, but no cutlery. The rules will tighten security but also increase the time to check baggage, enter airline terminals and board planes.

Curbside check-in will be eliminated. Jetliners will be searched by security officers before passengers get on. Passenger planes will no longer carry cargo or mail, to reduce the risks of bombs. And unattended cars will be towed if they are parked within 300 feet of a terminal.

The changes came as a law-enforcement official disclosed that a group of terrorists on at least one of Tuesday's four hijacked flights wielded sharp plastic knives and razor blades with handles, known as box cutters.

The airlines have long allowed people to carry on Swiss Army knives or perhaps a straight-edge razor. But the hijackings showed that even such low-grade weapons can provide enough force if brandished by determined terrorists.

"I could never understand why they allowed pocket knives to be carried aboard planes, because basically they are weapons," said Donald Egelston, a retired special agent and former security manager for Trans World Airlines.

The new security rules were negotiated between Federal Aviation Administration and Transportation Department officials and the chief executives of the country's major airlines in a series of conference calls beginning Tuesday night and ending today.

The Air Transport Association, the industry's lobby, suggested that even further measures be taken. The group said the F.A.A. should consider nationalizing passenger screening and revive the sky marshals program, which placed anonymous armed agents on selected flights.

Federal officials have long criticized the effectiveness of the security checkpoints, which are typically run by contractors working for the airlines.

That concern was magnified in May 2000, when Argenbright Holdings Ltd., a company that screens passengers at many of the nation's largest airports, pleaded guilty to federal fraud charges stemming from its hiring of 1,300 untrained security guards at Philadelphia International Airport. Dozens of the guards had criminal records.

Argenbright, which is still on probation, acknowledged today that it had screened the passengers Tuesday who took American Airlines flights out of Washington's Dulles International Airport in Washington and United Airlines flights in Newark.

An American plane out of Dulles and a United plane out of Newark, along with two flights from a Boston airport, were hijacked on Tuesday.

"We are unable to comment on any operational issues with regard to this tragic event," said Sara Jackson, Argenbright's marketing manager.