While a relentless onslaught of sunny days has many Washingtonians praying for rain, skywriter Wayne Mansfield would like a little less haze.

After postponing his latest stunt several times this summer due to overcast skies, Mansfield stitched his letters into a near-cloudless sky just south of the Mall yesterday afternoon, as tourists in line at the Washington Monument tried to guess the message.

"Compare? Company?" offered Cindy Kalbfell after seeing the first three letters spelled out. Both she and her husband, Ed--in town from Ohio with their two boys--are private pilots as well as avid sky-divers. Neither had ever seen skywriting in action.

Ed Kalbfell tried to imagine writing words in the sky, "upside-down and backwards, no less."

"It kind of gives those of us who do fly an appreciation of how hard that must be," Kalbfell said.

Mansfield's stunt yesterday over the Potomac--in which he spelled C-O-M-P-A-Q for client Compaq Computer--may seem like an old-fashioned way to get the word out for a state-of-the-art computer company.

But Pete Riordan, manager of "nontraditional advertising" for the New York ad agency BBDO, said corporations are showing a renewed interest in mediums like skywriting.

"Trouble is, there aren't many guys who can do this kind of flying, and it takes years to learn," Riordan said. "If there are a half-dozen people in the country who can do this, and do it well, I'd be surprised."

Skywriting, as an occupation, is rooted in the collective consciousness of two generations past. Mansfield's grandfather--once a daredevil barnstormer--went through five different planes before his death (peacefully, on the ground) at age 79. Wayne's parents bought their first biplane before they married in 1949. Theirs was a world before television, when aerial advertising was a new and prolific industry. In fact, Pepsi-Cola did most of its pre-TV advertising in the skies.

But with the advent of television came the beginning of the end for major commercial skywriting.

In 1962, when the Mansfields founded New England Aerial Advertising, they were one of a handful of skywriters still in the business. Wayne earned his wings at an early age, but initially shrugged off the corporate sponsors that kept his family's livelihood aloft. His works became the very object of rebellious expression.

One clear day during the Woodstock festival, for instance, found Wayne drawing peace signs in the air above the crowd. Around Christmas the next year, he was writing a message from John Lennon and Yoko Ono over their anti-war sleep-in up in Toronto: "Happy X-mas from John and Yoko."

Today Mansfield--now 52, president of Boston-based Aviad Corp., and father of two--is much more comfortable with corporate clients. The company he inherited from his parents 20 years ago has expanded into banners and starboards (lighted signs at night) as its main breadwinners. Wayne now spends only about 2 percent of his in-air time skywriting.

And there's a reason: The success of any skywriting attempt is largely dependent on the fickle whims of the weather.

"If it's cloudy out, you can forget about 'Happy Birthday Susan,' " Mansfield said. "For most locations, there are only usually about 10 days a year that are ideal for skywriting."

At more than two miles above the Earth, vertical air currents and thermals can quickly make alphabet soup out of any message.

To combat this menace, Mansfield said, he must often lean his letters into the wind, starting at the end of the message and working toward the beginning. Then there is the tricky task of writing everything backward, so that the writing can be read left to right from the ground. Even then, he said, not everyone will be seeing it perfectly.

Traveling at speeds of more than 160 mph, his small plane must stay at or above 10,000 feet (most small planes cruise at around 1,500 to 2,000 feet), so that the paraffin wax and water vapor that forms the "smoke" behind the plane can become cold enough to freeze.

Each time he takes to the air to write, he said, there is a strange paradox at work: Mentally he is at once airborne and on the ground, creating the message and imagining the many reactions to it.

"I'm sort of like a speechwriter who anticipates the words before they're spoken . . . out in the crowd, but also all by myself."

Mansfield is quick to point out that most modern-day skywriters are technically "sky-typers."

Sky-typing is done by five planes flying in formation. The middle plane has an onboard computer that controls the devices that activate the "smoke" in the other four aircraft. The letters are printed in a kind of dot-matrix style where each is composed of small cotton ball-like puffs. The entire "typed" text--usually consisting of up to 20 characters--can be completed in about the same time it takes to create even a single letter in traditional, looping skywriting.

Sky-typing may have the advantage of speed, but skywriting, Mansfield says, grabs the viewer in a more seductive way, slowly spelling out the text.

"Where else can you get so many people to stare at one ad for up to 10 minutes at a time? You can easily get pulled in, waiting for the message to be complete, or guessing what it's going to spell out." As an advertising medium, skywriting does have an impressive reach. At a scale of up to five miles wide and a half mile high, the text can be seen up to 25 miles away.

But to Wayne Mansfield, none of that really matters. These days, he's more concerned over whether the family tradition of flying will one day dissolve like so many wispy letters in the sky.

Wayne's son Ian, 17, said he hopes to pursue a career in advertising, and has already penned some successful campaigns for his father's company, but he is not a pilot.

"From an early age, I've been sitting around reading the Advertising Week magazines he brings home all the time, so it's certainly rubbed off on me," he said.

Ian suggested his sister Lucy, 13, has too grounded a personality for flying, and that she is more interested in the sciences.

"She's very smart. She definitely wouldn't go into the business," Ian said.

In the end, Ian offered the kind of testament that would do any dad proud.

"It's not that I don't enjoy flying," Ian said. "I really do. I just don't have the passion for it that my father has."