TRAVELERS UNITE LET'S ROUT THE LOUTS.

Byline: Adam Bryant The New York Times

Maybe it was the time Janice Lee Maniatis watched somebody changing a baby's diaper in the seat next to her. Or when she started noticing people walking about planes barefoot. Or perhaps it was after she was asked for the umpteenth time to store someone else's baby seat or carry-on bag in front of her feet.

At some point, Maniatis, a frequent flier and management consultant based in Naperville, Ill., decided that far too many passengers now check propriety at the door when they get on a plane.

"Passengers have become extremely rude," she said. "It's the new etiquette."

Planes are more crowded than ever. Airlines have cut out meals on short flights. Fearful of losing their bags or unwilling to wait at baggage claim, passengers are fighting over space in overhead bins. Boundaries of taste are overstepped, personal space is invaded, and tempers get short.

How to cope, and ease the burden of flying? Here, based on interviews with passengers and flight crews, are some suggestions for basic airplane etiquette which, if adopted, would make the skies friendlier, or at least tolerable.

The trouble starts when travelers ignore the so-called sizer boxes at the gate. These boxes, which are intended to help determine whether a bag is too big for overhead bins, are used by many travelers as convenient trash bins instead.

Once passengers are aboard, the hunt for space begins, giving rise to a pet peeve of many fliers - other passengers who push aside their carefully arranged bags in the overhead bins, or pile their bags on top of neatly folded jackets and coats.

A few points of bin etiquette: Minimal rearranging is permitted if done with care. Stacking is also allowed, as long as lighter objects - coats, small shopping bags - are placed on heavier, sturdier bags. If you are planning major reconstruction, ask the permission of the person whose bags you plan to move. Treat others' luggage as you treat your own.

If you are carrying a bulky backpack, be careful when you turn around; it's easy to hit seated passengers with the backpack.

Respect the rule that limits carry-on luggage to two pieces. George Brakeley, a consultant on fund raising for nonprofit organizations, said he once saw somebody bring enough luggage to fill an entire overhead bin. When he complained to the flight attendant, she simply shrugged. Flight attendants say they are prevented from enforcing rules by pressure to get flights in the air on time.

The fight for space may continue at your seat. Because planes are now no bigger than they need to be on any particular route, that middle seat that was once often empty is now regularly taken. So who gets the armrests?

Here's one suggestion: The middle passenger is entitled to the armrest next to the aisle seat. The person in the window seat has the right to time-share the armrest bridging the window and middle seat. Some frequent fliers prefer a simpler rule: If you are there first, it is your armrest until you move your arm away.

Finally, be sensitive to long-legged passengers behind you. As airlines have tightened up the leg room between seats, reclining can put the people behind you into an involuntary fetal position.

Another gripe of long standing is the chatterbox who keeps on going even when you make it clear you don't want to talk. Those using telephones on the plane should keep their voices down so that other passengers don't have to learn about the insurance business, too.

The practice is hardly glamorous, but more people are toting food on flights, either for health reasons or because airlines have cut back on meals. Frequent fliers and flight attendants consider this to be acceptable if not downright necessary.

So bring something from home, or pick something up from airport vendors, who are generally expanding their offerings. But nothing too pungent, please, out of respect to your seatmate. And pitch out your refuse when flight attendants come by with a garbage bag, rather than leaving it under your seat.

Airlines do not carry baby food on board. Attendants hate it when passengers store dirty diapers in seatbacks or hand dirty diapers to them. They suggest putting diapers in an airsickness bag and disposing of them in a bathroom trash bin.

On short flights, attendants say they are often so busy and harried that they reserve pleasantries for people who are nice to them. If you are among them, you may get an extra hermetically sealed biscuit.

Yet as much as some flight attendants say they try to connect with customers, don't expect to be asked "How are you?" Flight attendants who once asked this no longer do so because many people interpret the question as an invitation to unload the litany of injustices they have suffered, particularly in coach class.

Jostling to get off the plane - and on the plane, for that matter - is now a fact of life, because many airlines are hustling passengers on and off to squeeze in an extra flight or two a day. If you resent being nudged from behind, consider telling the perpetrator that you are claustrophobic and need more room.

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Photo No caption (Color--passengers on an airplane)