By the window of the Potomac Post Office a hand-lettered sign bears a tartly worded appeal to the wealthy and -- one might think -- well-mannered populace of this rich and woodsy Maryland suburb.

". . . Such behavior as kicking the door, yelling and cursing at the clerk when we are closed may pass virtually unnoticed in the ghetto," says the sign. "Here in Potomac, however, it is astonishing. Let us behave with the decorum that befits our station in life."

Teri Conlan, the 24-year-old clerk who two weeks ago taped up her class-conscious petition, apparently on the premise that there is a connection between money and civility, says she did not mean to insult people not so fortunate as to be buying their postage in Potomac.

She was simply sick of suffering the abuse she says was heaped on her by Potomac patrons who over the last three months have ranted and cursed in her face, stamped their feet and thrashed her window shade and, in their pursuit of postal services, generally seen fit to treat her "like a stamp machine."

For Conlan, a brown-haired Gaithersburg woman who was raised in a middle-class family, attends classes at Montgomery College and works six days a week as a postal clerk, and who held a notion that "upper middle class people have been raised to have good manners," it was a rude awakening.

"Basically, all I do is sell stamps, mark packages and take abuse," she says.

Conlan's encounters have occurred in a small post office sandwiched among fuse boxes and plumbing in the back of the Potomac Village Pharmacy. A substation of the Rockville Post Office, it is run by the pharmacy under a contract with the Postal Service. Conlan, the only clerk, can't forward mail, change addresses, trace lost articles on assign boxes.

These inherent limitations, Conlan says, don't seem to faze her male customers, but upset a lot of the women who come in.

"It's almost always the women who give me a hard time, and they're almost always wearing furs," Conlan says. "People here have maids and they're used to being waited on. They don't say please or thank you. They demand. I don't know if they enjoy the feeling of having someone wait on them or they're so used to it they don't realize it."

She says she decided to "get her feelings off her chest" two weeks ago after a fur-bedecked suburbanite badgered her so badly she went home in tears.

The post office had been closed five minutes and Conlan was filling out a report when a woman came up and rattled the shade pulled over the stamp window. The woman began a conversation through the shade with Conlan, whom she could hear working.

"I was at the door at quarter of five," the woman said. "You could have seen me walking toward you." Conlan demurred. The woman tried another approach. "Your watch is wrong." Her voice began to rise. "Gimme a good reason why you can't wait on me," she said shrilly, and began to splice her sentences with expletives.

"Goddammit, while you're wasting your time talking to me you could be waiting on me," the woman sputtered. She demanded Conlan's name and the number of her supervisor, which she received, and then loudly cursed the clerk's "nerve" and stormed off.

Conlan peeked around the door and saw the woman -- and the fur coat.

"That was the last straw," she said. "I wasn't going to come into work the next day. That's when I put up the sign."

She said she found no racist overtones in the message, and only one of her customers, a black woman, complained that the sign was a slur on ghetto residents. Conlan says the woman told her, if things were as bad as she said at the post office she might be giving ghettos a worse reputation than they deserved by comparing them to Potomac.

"If I had thought of the sign as a racial slur I wouldn't have written it," Conlan says. "I was raised in a house where bigotry was non-existent."