What if someone called up out of the blue and promised you several hundred thousand dollars over the next five years for doing just what you've been doing -- or nothing at all?

Could you handle it? All that sudden media attention, the financial planning headaches, the calls and letters from around the world, the envy of colleagues, the guilt, the self-doubt, the sense of "why me?"

The 223 MacArthur fellows who have received such a dream phone call in the past six years seem to be coping just fine, thank you.

"First, it's a great sense of liberation," said Horace Freeland Judson, a writer and historian of science at Johns Hopkins University, who has two books "hanging fire," two kids in college and a leaky roof on his Baltimore home.

"One is free to do what one has known for some time one ought to be doing," said Judson, 56. "For me, that's writing books. It's writing about things that are not simply story ideas, but real stories.

"And it means I don't have to worry about mending the roof."

The awards, commonly known as "genius grants," are conferred by the John D. and Catherine T. MacArthur Foundation in Chicago, which secretly seeks out potential recipients with the help of 100 anonymous nominators around the county. The five-year grants, ranging from $150,000 to $375,000 for this year's winners, are intended to give outstandingly talented and promising individuals "the freedom to create."

Winners have ranged in age from 18 to 82 and have included physicists and poets, musicians and mathematicians, as well as a high-school teacher, a sculptor, a magician, a woodworker, a clown.

"My God, he'll really be impossible now," Judson's sister joked to his wife at a celebratory party last week. But Judson dismissed the "genius" label.

"The word is silly," he said. "Genius is as genius does. It's accomplishment that matters. I've got to prove it now."

Beyond the money -- $335,000 in Judson's case -- and the recognition, what really distinguishes the MacArthur grants is their no-strings-attached aspect.

"You can't apply for it. And once you've got it, there are no obligations," he said, repeating the last two words. "Roll those words around in your mouth for a moment. That's the perfect marriage of sound and sense. Pure poetry."

But could the windfall take the edge off a recipient's creativity?

Sam Maloof, 71, a self-taught woodworker who designs and makes furniture in a small shop in Alta Loma, Calif., won a MacArthur grant two years ago. He worries a bit less about the cost of getting sick, but still works 10 to 12 hours a day and says his life and work are little changed.

"It lets me do whatever I want," Maloof said, "but what I want to do is make furniture."

Maloof, whose work appears in leading art museums around the country and is represented by a walnut rocker in the White House, said his award was "not to me alone but one that recognizes the crafts as a whole in the United States."

The lack of requirements, ironically, could impose a special burden on some recipients, psychologists say. And some highly successful people become victims of their own levels of aspiration and the escalating expectations of others.

But MacArthur winners are chosen in part for their very commitment to excellence and hard work.

"It's not like winning the lottery," said David Glass, professor of psychology and director of the doctoral program in personality and social psychology at State University of New York at Stony Brook.

Unlike the lottery, which is based on pure chance, a MacArthur award depends on past accomplishment and future promise, Glass pointed out. Nor is the MacArthur award like the traditional foundation or National Institutes of Health grants, for which individual researchers must apply in a lengthy, detailed process.

"In science, the really creative breakthroughs don't come from research proposals, but from a proven investigator following his or her nose," Glass said. "That requires some relief from the pressure of constantly writing grant proposals." Which is exactly what a MacArthur award offers.

"First, it feels wonderful, it genuinely does," said Dr. Stuart A. Kauffman, 47, a physician and theoretical biologist at the University of Pennsylvania Medical School.

But the $290,000 award Kauffman received last week also gives him "a sense of obligation" -- not to do anything in particular but to continue doing his best work.

"It's a kind of stimulus that says: Go for it. Make it happen," Kauffman said.

Among other projects, Kauffman and his colleagues are applying evolutionary theory to newly created genes and proteins in a method that could lead to development of vaccines. He is also working with a diverse group of scientists to define "the science of complexity."

Creativity in any field, Kauffman said, is "taking yourself seriously."

"You might say, 'I'll take the money and sail around the world,' " he said. "Well, yeah, you might. But that's not what your life is. What I'm going to try to do is more of my work, not less.

"The pressure it puts on you is to take yourself seriously and do whatever you do well even better. It's a form of validation."

No one has studied the psychological effect of such a windfall on creativity, said James E. Birren, a psychologist at the Andrus Gerontology Center at the University of Southern California.

"We all work in a highly socialized environment," Birren said. "Our peers are always shaping us up.

"But with an award like this, the expectations have to come solely from within, and this is a whole new ballgame. We don't know much about this."

MacArthur award winners, Birren said, tend to be "inner-directed" people who are unlikely to change much merely because of five years of unconditional financial support.

"If it were longer than five years, I'd be more worried about the lack of peer review," Birren said.

But the unrestricted nature of the MacArthur grants is a key part of their appeal.

"All there is is a phone call and a series of checks," said Lester Brown, president of Worldwatch Institute, who won a MacArthur award last year. "No paper to fill out, no award ceremony."

And no requirements.

Brown turns over most of his MacArthur check to his institute, which analyzes trends in the environment, food, population and economics. "I considered getting a new bicycle, but I decided it wasn't worth it. The one I have is 12 years old and works fine."

Overwhelmed by the outpouring of congratulations from around the world, he concluded that people find particularly appealing the idea of an award that one can't apply for. They see it, he said, as a "social celebration of commitment or creativity."

And despite all the jokes, most MacArthur winners shrug off the "genius" label.

"I define genius the way Einstein did -- as 1 percent inspiration and 99 percent perspiration," Brown said. (Actually, it was Thomas Edison.)

Deborah W. Meier, a public school teacher and founder of alternative schools in East Harlem, N.Y., was annoyed when a secretary interrupted her staff meeting 10 days ago with an insistent call from the MacArthur Foundation.

"I thought it was someone telling me about another form I had to fill out," Meier, 56, recalled. "I was prepared to yell at whoever it was."

Whoever it was told her she had just won a five-year grant of $335,000. Since then, she has received hundreds of congratulatory calls from friends and even fellow teachers she has never met, who see the award as an honor for teachers everywhere.

She described her first reactions as "disbelief and joy -- plus fear. But when people call to say how wonderful it is, that is the wrong time to tell them your fears." Fear that it might be a mistake. The old Puritanical fear of too much good luck -- "knock on wood, and all that." Fear of being singled out.

"That word 'genius' -- it's a little bit scary," Meier said.

She is puzzled and disconcerted by a common reaction among friends -- that now she won't have to teach in public schools anymore.

"When a writer gets an award, do people say now they can stop writing? They go on doing the most important thing in their life.

"For me, that's teaching."