The notice plopped softly through Alice Sheldon's mail slot in McLean last May. Until that morning, she had thought she was "an old lady who wrote science fiction stories." But the Fairfax County government was writing to say, in its best mimeographese, that she was really a business.

Like a dry cleaner or a Chinese restaurant, Alice Sheldon had to get a license.

Sheldon laughed at first. Surely this was the fruit of a computer whose dials were permanently set on April Fool's Day.

After all, although she had published 40 novellas and short stories, Alice Sheldon could hardly be mistaken at the bank for her write-it-raunchy namesake, Sidney.

True, she got residual royalties, but less each year than the August air conditioners devoured. Meanwhile, Hollywood had never shown an interest in the movie rights, to put it charitably.

Moreover, Alice Sheldon couldn't properly be accused of being a business because she hadn't written anything but letters for two years.

So she called the Fairfax Office of Assessments to tell the troops that it had been a good gag, and would they now please call it off?

No gag, said they.

The law was the law, and had been on the Fairfax books since 1970. Either Sheldon applied for a "specialized occupation license" right away, or she'd risk a fine of as much as $300, or a jail term of as much as 30 days, or both.

To which Alice Sheldon says two things:

One: "I have since decided to refuse to apply."

Two: "It is my hope to achieve jail."

"Maybe I spent too much time interrogating Luftwaffe officers in Germany in 1945 (as a psychologist)," Sheldon said. "Maybe I'm paranoid. But I don't like it."

That's nothing new, says Paul Smith.

Smith is director of the license division of the Fairfax Office of Assessments. In English, that means his job is to tell the irate Sheldons of the world that Fairfax County isn't kidding. He says none of them likes it.

Poets? "Oh, yes, we've had poets apply for licenses." And musicians? "Sure." And fingerpainters? "Yup." Even snake oil salesmen? "In one form or another, yes."

All have tried sweet-talking or threatening, Smith said. All have eventually broken down and gotten the license.

"Science fiction writers," Smith declared, "are no different from anyone else."

But Smith may have met his match in Alice Sheldon. Not only is she not your everyday capitulator to silly tax laws, she isn't anything close to an everyday science fiction writer.

First and foremost, she has sold every word she has ever written, except a novel "whose main distinction is that most of it drowned" in a warehouse flood last winter.

Sheldon has written under the pseudonym of James Tiptree Jr. throughout her 12-year career-and she delights in revealing that she lifted the nom de plume from a marmelade jar.

Sheldon describes herself wryly as "world famous" in the world of Sci Fi - "meaning that at least 300 people know the (Tiptree) name."

But Sheldon has gone to considerable lengths to keep her true identity secret. For instance, a bunch of fans once tried to stake out Tiptree's McLean post office box a few years ago, to catch a glimpse of their idol. Tipped off, Sheldon arranged to be in British Columbia.

The license Fairfax wants Sheldon to buy does not cost anything. "It is simply a revenue-producing device so we can know who's out there, and tax them," Smith explained.

License-holders are taxed at the rate of 31 cents per $100 of gross income. But if the collectible tax is less than $10 a year (gross earnings of $3,226 a year or less), a license-holder owes nothing.

Alice Sheldon earns so little that she wouldn't owe any tax. But to Sheldon, it doesn't matter. The question is one of "that vague but hopeful area known as my constitutional rights," she said.

Besides, Sheldon asks, what if she wanted to write a piece of science fiction satirizing pheasants? And what if the license-issuer's son happened to collect pheasants? And what if he told Daddy one day that he didn't like this Sheldon writer person, and why didn't he deny her a license? All strictly on legal grounds, you understand.

Paul Smith says that no one has ever been prosecuted in Fairfax for failure to obtain a "specialized occupation license." Reason: it's never gotten that far. Most resisters have had so little income that they've finally said the heck with it;it won't cost me any tax anyway.

"If all else fails," Alice Sheldon says, "I might train a skunk to carry (the application) in." But that is a joke, and her determination isn't.

Alice Sheldon is ready to go to prison if she has to.

Is Fairfax County truly ready to put her there?