The Federal Aviation Administration imposed regulations yesterday requiring airlines to limit carry-on baggage and make certain that items are properly stored before an airliner leaves the boarding gate.

The agency said "too much baggage is being taken aboard some flights {and} being stowed improperly, creating unsafe conditions" because airlines have become "lax in their compliance" with existing baggage requirements.

Each airline within six months must establish a limit on how much carry-on baggage will be allowed, and put into place a screening system, the agency said.

Flight attendants for years have complained that airlines allow too many bags and large items aboard aircraft, making it impossible to properly store them during flight and posing a safety hazard.

"We've seen truck tires, Christmas trees, even a drive shaft from a BMW, and often passengers just bringing four or five bags on board -- which is not only unsafe, but inconveniences the other passengers," said Matthew Finucane, safety director of the Association of Flight Attendants.

"Some passengers have evidently come to expect that they will be able to carry on almost anything," the FAA agreed.

While the new requirements do not establish specific limits on size and number of items that will be allowed on board, the FAA told the airlines they must:Establish their individual, government-approved limit on the size and number of items that may be brought aboard, depending on how much space is available in various aircraft. Scan each passenger's bags before boarding to assure that the limit is not exceeded. Keep the aircraft at the gate and at least one cabin door open until flight attendants have confirmed that all baggage aboard the plane has been properly stored.

The FAA said it rejected recommendations from the Association of Flight Attendants that a single, federal limit on bags be imposed because the agency felt that different aircraft can accommodate a widely differing amount of carry-on items.

But it said a specific standard, establishing the number of bags and size of each item, was needed so that flight attendants are not forced "to stow excess baggage in lavatories, galleys and other unauthorized areas."

The rule-making for carry-on baggage, which began three years ago, prompted thousands of letters to the FAA from airlines, passengers, unions and other interested parties. Travelers in recent years have pressured airlines to allow them to carry more bags with them on the plane because of concerns that their belongings will be lost as their flights go through busy hub airports.

Airlines have sought to accommodate these travelers and in many cases have expanded storage areas. The FAA said, however, that 90 percent of the letters it received favored tighter controls.

There were critics, nevertheless.

Jewelers and musicians complained that the limitations would hamper their businesses because they might not be able to carry sample cases or instruments.

The International Association of Duty-Free Shops, the city of Los Angeles and the state of Hawaii complained that it would discourage people from buying duty-free items at airports. Airlines also argued that preboarding screening would add to delays.