KUTZTOWN, PA. -- As an architect living in the British Virgin Islands in the late 1970s, James O'Halloran was enjoying the good life.

He was designing lavish million-dollar vacation homes for the world's well-to-do and spending his free time relaxing on Tortola's island beaches and on Ragtime, his antique 71-foot yacht.

But something was bothering him.

His toothbrush just wasn't doing the job.

The handle wasn't shaped right. The head was too small. His mouth didn't feel clean.

He had been scrubbing his teeth with the latest in toothbrush technology -- the Reach brush introduced in 1977 with an explosion of advertising fanfare -- but it wasn't enough.

O'Halloran thought he could do better.

What he came up with was a jumbo brush that "combines the architecture of the hand and mouth," he says.

Over the next decade, O'Halloran's toothbrush evolved from a crude prototype he carved out of a hunk of beeswax into brushes with brightly colored handles and bristles, funky designs and a big resting place for your thumb. The handle is a thick combination of smooth curves and hard lines. They even come in right- and left-handed models.

The enterprise itself has grown into Radius, a 12-employee company based in sleepy Kutztown; Radius sold more than 250,000 toothbrushes last year.

The toothbrush's most obvious difference is its size. Its head, cocked at an odd angle, measures roughly the size and shape of a slightly elongated silver dollar.

"It's huge," said Kevin Foley, O'Halloran's partner and former co-worker at Michael Helm Architects on Tortola. "Most people look at it and say, 'My God, how in the world am I going to get that thing in my mouth?' "

Radius -- founded in 1982, about five years after O'Halloran's first vision of a better toothbrush -- is still a small player in the $2.8 billion-a-year oral-hygiene business, commanding about 1 percent of the $300 million to $350 million that American consumers spend on toothbrushes each year.

But its presence has been growing steadily.

Radius expects to log sales of $925,000 this year, an increase of more than 45 percent over 1989 and a five-fold jump since its first year. Its toothbrushes are sold in more than 3,000 stores in the United States and are especially popular on the West Coast and in health food stores.

The Radius brushes have soft, thin bristles that reach small crevices along the gum line, O'Halloran and Foley say, and they claim that the large, angled head cleans teeth more effectively than traditional brushes.

It was touted as the Most Original Use of Design at the Accent on Design show in New York in 1984. The sailing has not always been smooth, however, for a company whose founders readily admit that their venture initially hinged on a good idea and little else.

The toothbrush is pricey -- about $8.95 in retail stores, well above the average of less than two bucks for most toothbrushes.

And Radius still has not broken into major supermarkets, where more than half of the country's toothbrushes are sold.

"We learned early on that it was going to cost more to make the Radius and that having a $1.75 toothbrush was going to be impossible," O'Halloran said. "So, instinctively, we started looking at upscale stores."

O'Halloran and Foley, both 48, worked together on Tortola for about five years before each launched his own design company. Though O'Halloran remained on Tortola and Foley moved to Puerto Rico, the two men kept in touch and continued to discuss the idea of starting their own toothbrush company.

They raised about $145,000 from 23 investors -- mostly friends -- and from the sale of the boat. In 1982, they abandoned their architecture practices and moved to New York.

Starting Radius and designing the brushes was easy. Unfortunately, the partnership knew nothing about getting the product to market.

"We spent so much time and energy developing the toothbrush, we really didn't have any idea how to sell or market it," Foley said.

They budgeted about $20,000 for their first marketing program, purchased several mailing lists and hoped to start off with a bang in the mail order business.

"We got about two sales," Foley said. "The list we used was made up of a lot of department stores and they don't sell toothbrushes.

"It was a small detail which slipped by us."

Radius also suffered from manufacturing difficulties. A Massachusetts company that was making the brushes wanted to produce only mass quantities and had trouble adapting to special orders, especially for new designs and colors.

Foley and O'Halloran solved the problem by taking on the task themselves. Now, every brush is made in a converted feed mill in Kutztown that Radius bought in mid-1988 to escape the congestion of New York City.

"If you're interested in innovation, you have to make your own product," O'Halloran said.

In 1984, the toothbrush manufacturer Oral-B approached Radius about a possible buyout. The deal never came off, but Foley and O'Halloran had a little homework done for them. Oral-B officials had projected that Radius's market could grow to as much as $20 million annually.

Foley couldn't give his own estimates on such complex big-business calculations as market share and earnings potential -- "our distribution system is so illogical that it's hard to make a business plan about those things," he says -- but he believes Radius's growth will pick up steam as the product breaks in with bigger retailers.

"The growth curve is going to be much steeper in the next few years, no question about it."