Last week British designer James Dyson was merely the inventor of an innovative bagless vacuum that is cleaning up market share on three continents.

A Washington appearance at the U.S. Navy Memorial Theater on Sept. 24 drew 250 admirers of Dyson's industrial-strength function and form. The vacuum's chief innovation is the ability to suck dirt, pet hair and cookie crumbs out of carpets and into a clear plastic cylinder. For better or worse, the gleanings remain visible until the trap is emptied. Even bright accent colors can't make this contraption pretty.

By his own reckoning, Dyson is an industrial engineer, not a stylist. And that's why this week he's not only an inventor, he's a man taking a stand.

After five years as chairman of London's prestigious Design Museum, Dyson resigned in protest over what he sees as a drift from serious discussion to fluff. The ensuing debate has transformed Dyson into a force of conscience or the design world's Don Quixote, depending on one's point of view. Either way, he has staked out a position as the anti-stylist.

The London museum, founded in 1989 by Terence Conran, was the first of its kind to celebrate industrial design and manufactured products. Dyson liked exhibitions on civil engineer Isambard Kingdom Brunel and futurist-inventor R. Buckminster Fuller. But in the past three years, under Director Alice Rawsthorn, video game consoles, Manolo Blahnik shoes and Harper's Bazaar typography have filled its galleries. A September exhibition on pre-World War II society florist Constance Spry was the last straw for Dyson. Spry's innovations include cabbage leaves in vases and bouquets for the duke and duchess of Windsor's wedding.

In a letter made public on Monday, Dyson wrote to fellow trustees, including Conran, saying that frivolity was "betraying" the mission and "ruining the reputation" of the institution.

"It's a slippery slope downwards," Dyson warned Wednesday by phone from Germany, where his vacuum was inducted into the collection of a Hamburg museum.

Rawsthorn, a former Financial Times critic, declined to comment for this story. But the museum's Web site cites a mandate broadened to "design, fashion and architecture" and a mission to excite "everyone" about design.

Dyson retorts, "I think it's very sad that the original motivation is gone."

In his view, the danger goes beyond the price of admission.

"If we don't encourage interest in serious design and problem-solving and engineering, we don't inspire future generations of engineers and designers," he says. "It's the vital engineering that makes one company more successful than another, and gives one country an edge over another. In the end, it's the only advantage you have."

At 57, Dyson is his own evidence. An armada of patented dual cyclonic uprights and canisters have made him Britain's most visible design export since Conran launched Habitat shops abroad and Jonathan Ive landed at Apple. Dyson labored 20 years before conquering Europe and Japan (more than 10 million sold) and breaching the walls of Wal-Mart. Myriad patent and legal issues explain the title of his 2003 autobiography, "Against the Odds." The onetime interior design student at the Royal College of Art now advises his country's Department of Trade and Industry.

Over tea at the Hay-Adams -- and between passes of a DC14 Telescopic upright over the carpet -- Dyson explained that his machines are made in Malaysia by workers trained by Sony, which has since moved on to China. With the battle for low-cost manufacturing rippling across Asia, he says, design is the last competitive advantage that Western economies have.

"The big edge we have is not in producing cheaply or going into mass production," he said. "The edge we have is in technology and design. We're living by our wits."

If design museums shy away from explaining the guts of design, he worries, the next generation will perceive the designer as "little more than the creator of ineffectual ornaments." And what's left of Western industrial manufacturing will spiral into decline.

At the Design Museum, the spiral of visitors is upward, according to figures supplied by a spokeswoman. Whether numbers reflect a belated return to normal after 9/11, or a response to the new mix of exhibits is unclear. But the London museum is not alone in branching out. Design venues are edging into fashion, architecture and art. Others, including New York's Museum of Arts & Design (formerly the American Craft Museum) and the Bard Graduate Center for Studies in the Decorative Arts, Design, and Culture, have added "design" to their names. The Metropolitan Museum of Art has enhanced exhibitions of 20th-century design and brought fashion into the heart of the institution with "Dangerous Liaisons" and a Jacqueline Kennedy show.

At Washington's National Building Museum, Director Chase Rynd has expressed a desire to showcase architecture as art and sculpture, rather than structural engineering. But curator Donald Albrecht promises plenty of substance in a 2005 exhibition on "green" housing.

The Smithsonian's Cooper-Hewitt National Design Museum has embraced art and fashion. Director Paul Thompson, who preceded Rawsthorn at the London museum, declined to comment. But the Cooper-Hewitt is currently showing furniture by 18 artists, including Donald Judd. A spokeswoman called attention to a 2005 exhibition that will feature high-tech textiles.

Few product designers or engineers can claim to be household names. Television commercials may help Dyson. At his Washington appearance, which was sponsored by the Industrial Designers Society of America and the Apartment Zero design store, he was confronted by a fan who asked him to autograph her vacuum cleaner's instruction manual.

The question facing museum curators might be reduced to this: Would the crowd have flocked to see the designer of a flat-bottomed landing craft engineered to save soldiers from a repeat of the disastrous D-Day landing? Or to learn the intricacies of making a wheelbarrow travel on a ball instead of wheels? Dyson designed both products. But it took a familiar houseware, reinvented, produced in fashion colors and slickly marketed to spark the public's imagination.

That story almost has the makings of a populist museum show.

James Dyson, inventor of a bagless vacuum, resigned from the London Design Museum to protest the institution's de-emphasis of engineering, as seen in exhibitions on Manolo Blahnik shoes, far left, and florist Constance Spry.