Realtors have been called many names over the years, but the one that really drives them crazy is: "realtors."

You are supposed to capitalize the word, you see, and follow it with a symbol indicating that it is a registered trademark, like this: Realtor .

The real estate profession owns the word Realtor. They invented it early in this century, registered it as a trademark in 1950 and today guard it as a central element of their collective identity.

The word means an agent or broker who is a member of the National Association of Realtors. It is not a synonym for real estate agent, though it often is used that way by people who do not know better.

And it is just that generic use of the word that the NAR has been fighting for years, trying to ensure it avoids the dreaded fate of such former trademarks as "escalator," "brassiere" and "aspirin." Those words started out as the names of products made by particular companies, but lost their official U.S. trademark status -- in court -- after they passed into common speech as names for entire classes of products.

Realtor is in good company. Among other trademarked words perennially struggling to retain their original meanings are Kleenex, Xerox and Band-Aid.

"Our constant battle is to make sure it doesn't become like Xerox," said Anthony Carr, a spokesman for the Northern Virginia Association of Realtors, one of the NAR's member organizations. "People say, 'Oh get yourself a realtor,' when they mean get yourself a real estate agent."

The NAR may not face quite the challenge that the Xerox Corp. does in protecting its name from generic use, but the the word Realtor has its own special problems.

It was invented before public relations people learned that the strongest trademarks often are totally made-up words. "Kodak" is one of the best-known of what the experts call "fanciful" trademarked words. Because they do not initially carry other associations, these words are easier to defend against use in connection with similar products or services.

Realtor was coined in 1915 by Charles N. Chadbourn, a Minneapolis real estate broker who one day noticed a newspaper headline reading, "Real Estate Man Swindles a Poor Widow." According to an NAR historical account, the swindler in question was not a member of the local real estate association, "but only an obscure speculator" bringing dishonor on the whole profession.

Incensed, Chadbourn proposed at a national association meeting the following year that the group adopt his word as a professional title. His goal, according to NAR senior counsel Ralph W. Holmen, was to distinguish members "from garden-variety real estate agents, whom he regarded basically as scoundrels."

Today the NAR stresses that Realtors -- in the true sense of the word -- are people who, by virtue of their membership in the association, subscribe to its professional code of ethics. The title is supposed to be a kind of badge of respectability, but the problem is that it sounds generic. Though an original coinage, it has a clear etymological connection to the realty business. In short, it is not "fanciful."

"It is more descriptive than most registered marks," said Michael Finn, communications manager for the U.S. Trademark Association in New York, which has about 2,600 members including many trademark-owning organizations.

Because its meaning and uses are so easily expanded, Finn said, Realtor is "a weaker mark." (Another trademarked word having a rough go with generic use, he said, is Rollerblade, the name of a specific brand of in-line roller skates.)

To make matters worse, Realtor is generally used as a noun, whereas, according to Washington attorney Bruce Tassan, who specializes in intellectual property law, trademarks are strictly defined as adjectives. He cites "Kodak film" and "Exxon gasoline" as examples.

"You don't want a trademark to ever be used as a noun, because if it's used as a noun, it's more likely to be treated and perceived by the public as the apt {generic} name of the product or service," Tassan said.

But why all the fuss? So what if Realtor loses its original meaning and its connection to the NAR?

The association's answer to such questions comes in its 65-page manual on how to defend and properly use the word. Basically, it all goes back to Chadbourn and the swindler: "The usurpation of the name REALTOR," the manual says, "would make the image of the REALTOR indistinguishable from that of the least ethical, least responsible, least competent, and least concerned real estate practitioner."

More simply, the word was and is a key part of efforts by real estate agents and brokers to be treated as members of a true profession. The most famous fictional Realtor of all, Sinclair Lewis's George Babbitt of the 1922 novel "Babbitt," put it this way: "Makes me tired the way all these doctors and profs and preachers put on lugs about being 'professional men.' ... First place, we ought to insist that folks call us 'realtors' and not 'real estate men.' Sounds more like a re'lar profession" The novel was written before capitalization of the word had taken hold.

There also is the matter of money. Beyond respectability, the name was intended as "a badge of exclusivity," said Marc A. Weiss, director of Columbia University's Real Estate Development Research and an authority on the history of the profession.

At the time the name was adopted, Weiss said, real estate "was an industry that was unbelievably competitive, and the question was how were they going to keep from being undercut in terms of commissions ... and all that kind of thing. So they tried to reduce competition and make it somewhat more monopolistic."

After a trademark has been registered and used for five years, it is considered to be the property of its owner. That ownership can then be lost only if it is abandoned, found to have been obtained by fraud, or becomes generic. Since generic use is difficult to prevent, and there is no government enforcement of trademark status, trademark owners live in fear of losing their words and symbols.

"It's up to the company to protect it," said Lawrence Urdang, editor of the language magazine Verbatim, published in Old Lyme, Conn. Urdang noted that it is "almost impossible to legislate what people say. ... It really doesn't have much tooth to it, this whole business."

Urdang ought to know. He was involved in a legal battle some years ago against a California computer-products company that, three years after the founding of his magazine, started making blank diskettes named Verbatim. They reached an understanding, and both companies still use the name.

Determined to hold on to its own word, the NAR packs its manual with directives on how to use Realtor in correspondence, advertising and even conversation. For example, it notes that "when asked what he does for a living, an unthinking Member may answer incorrectly: 'I am a Realtor .' "

Right word, but a dangerously generic usage. The proper way to say it, the manual says, is: "I am a real estate broker and a Realtor ," to emphasize that they are not the same thing.

Likewise, the stylized "R" logo that often appears in real estate company advertising, and which is separately registered as a trademark, is supposed to be used only in very particular ways.

"Never redraw, round the corners, reshape, trace, tilt, intersect, photographically alter or otherwise distort the REALTOR

Logo," the manual cautions, and its recommends that the logo be rendered in the profession's official colors, Realtor Blue and Realtor Gold.

Violators beware. Local NAR member associations nationwide are under orders to police uses of the word Realtor and intervene when necessary. The first step, Holmen said, is a letter to the offender "pointing out to whomever it might be the error of their ways, so to speak."

If that doesn't work, the legal staff at NAR headquarters in Chicago is put on the case.

Holmen said he finds himself involved in trademark enforcement "all the time," and that one of the legal associates in Chicago spends up to half his time writing warning letters and negotiating with violators.

The protective effort appears to be working. The association has filed lawsuits in only a handful of cases, Holmen said, and there are none pending now. Tassan, who defends such trademarks as the FTD mark of the Florists' Transworld Delivery Association, said the small number of cases concerning Realtor indicates the NAR must be doing something right.

Indeed, major English-language dictionaries, as well as the stylebooks of many news organizations, including The Washington Post, define the word along NAR lines and call for it to be written with the first letter capitalized. Finn said his group does not ask that the press print the registration symbol after trademarked words.

"I had a newspaper guy tell me one time that the only other word they always have to capitalize is the word God," said Bud Smith, NAR executive vice president.

The same man, a reporter for the Cleveland Plain Dealer, got around the awkwardness of the capitalization by trying to use Realtor only as the first word in a sentence, Smith said.

The Realtors' vigilance may safeguard their word's trademark status, but it probably cannot resolve an even trickier issue: how to say it.

"People mispronounce it 'REE la tor,' " word expert Urdang said.

As you might expect, the NAR manual has a section on just this subject: "Irrespective of local dialect and custom, the term REALTOR has but one pronunciation: REAL tor."

If that decree appears a bit strict, just remember: It's their word.