Strained relations between District firefighters and their leaders escalated into a three-day scolding for the firefighters after a derogatory bumper sticker mysteriously appeared on Fire Chief Theodore R. Coleman's city car Friday.

The three-line bumper sticker, which reads "D.C. Fire Department. It's Not Just a Job; It's a Joke Too," has been sold by some firefighters for $2 each to benefit the Washington Hospital Center's burn unit.

Many firefighters were privately amused when news of the prank began to circulate.

But their good humor quickly faded when Coleman angrily responded by dispatching deputy chiefs to each of the city's 34 fire stations during the weekend to reprimand on-duty firefighters about the incident.

"I don't consider it a joke," As- sistant Fire Chief Howard Dixon said yesterday.

One firefighter who did not want to be identified said that he and others were summarily lined up at close to midnight on Friday when Deputy Fire Chief Michael C. Tippett arrived at his station with the message from Coleman.

"The on-duty deputy fire chief {Tippett} made rounds of all 34 stations, getting some us out of bed," the firefighter said.

"They hit two bells, we slid {down} the pole and we get this long spiel about bumper stickers. After he left, we all laughed."

"I think it's a genuine overreaction to a silly situation," said another firefighter, who also asked not to be identified for fear of retaliation.

But Coleman said he did not think that the deputy fire chiefs were overreacting.

"There are rules and regulations covering the kinds of attitudes that firefighters have toward District government. The District govern- ment pays those firefighters a good salary to perform a certain function. And I don't think the citizens of the city should take these actions lightly either," he commented yesterday.

Any firefighter who thinks working for the city is a joke, Coleman said, "should resign or quit."

"What is being said to the men is we're about a serious job and this is not the way to go about it," Dixon said yesterday.

"The bumper stickers are not funny and they're not condoned by the department."

Any member of the department who was responsible for affixing the sticker to Coleman's car, Dixon said, would be guilty of defacing government property and liable for penalties beginning with a 30-day suspension.

"But we're not threatening anybody with suspension," he said.

"The deputies are giving talks out there. They're not threatening anybody, just telling them."