What do you call the white tissue paper used for blowing noses? Most people say Kleenex.

What do you call the hard surfaces used for kitchen counters? Most people probably say Formica.

What do most people say when they're going to photocopy something? They're going to Xerox something, most likely.

Without mentioning any of those examples, Federal Trade Commission member Paul Rand Dixon said yesterday the agency may begin challenging the exclusive rights accorded some trademarks that have become so common they now may be a part of the language.

Although Dixon agreed that trademarks serve a useful purpose in the functioning of the economy, he noted that trademarks may be abused, or their valuable function diminished, sometimes through no fault of the holder.

"This occurs most often when a trademark, over time, becomes the common descriptive name for a product, that is to say, when it becomes generic," he said in a speech prepared for delivery to the United States Trademark Association meeting in Palm Beach, Fla.

The word "linoleum," for instance, was once a trademark but the courts held that it had become generic and that it was being monopolized unfairly by the trademark holder. Among other words that have lost their special trademark protection are shredded wheat, cellophane, aspirin, cola, trampoline, yo-yo and brassiere.

"A trademark is a perpetual monopoly over one segment of the most powerful means of influencing the thought and behavior of American consumers over invented - the English language," Dixon argued.

Consumers may seek out and pay for brands using the trademark as a generic word without giving adequate consideration to similar or identical products of competitors because the competitors' products appear to be something other than "the real thing," he noted.

"The law confers and protects such monopolies in the first place in the interests of maximizing the output of our economy, and if a trademark should happen to stop performing the useful function that it has been performing, by becoming generic, then it seems to me appropriate for the law to withdrew protection from the mark."

Under the 1946 Lanham Trademark Act, the FTC has the authority to petition the Trademark Trial and Appeals Board to cancel registered trademarks on one of six grounds. Although the FTC has petitioned and won cancellation of some marks on several of the grounds - such as those fraudulently obtained or used to misrepresent the source of goods or services, it never has sought cancellation of trademarks on one of the grounds - becoming the common descriptive name of an article or substance.