Just as liquid-crystal-display TVs are getting to be big sellers, engineers are starting to see a limit on how big they can build them -- and that could throw a wrench into the industry's growth model.

Flat-screen fabrication delicate. In making both LCD and plasma screens, chemicals are pressed between two sheets of glass to form images. The glass is flat, clean and thin -- less than a millimeter thick in the case of LCDs. Just as microscopic contaminants damage the circuits of a computer chip, a bit of dust can ruin an LCD or plasma panel.

Yet the size barrier the industry is approaching is as low-tech as they come. Ultimately, the glass sheets, or substrates, will be too large to be moved to the plant that cuts LCD screens out of them.

That logistical limit could have a major impact on the future of the dozen or so fast-growing manufacturers, all in Asia, that make the panels for LCD TVs. Since breakthroughs in 1999 and 2000 allowed cost-effective production of larger LCDs, engineers have been racing to make bigger sets. Samsung Electronics Co. of South Korea this year built demonstration models of an LCD TV with a 81-inch screen and a plasma-based TV with a 102-inch screen.

It is most economical to cut lots of panels out of a single glass sheet. For example, the sixth generation of LCD glass sheets, the kind used in most of the new plants opened in the past year, yields eight 32-inch panels, while the seventh-generation sheets, used at a plant that opened in South Korea in March, yields 12.

But manufacturers attract consumers with their bigger screens -- which, for the time being, also yield high profit margins -- and for that, too, they need ever larger glass plates. They have sought to keep outdoing themselves to stay ahead in what always threatens to tip over into a commodity business.

Samsung plans to build LCD screens as large as 100 inches. On the way to that goal, the company will use glass panels the size of a king-size bed in its eighth-generation plant and larger than that in its ninth-generation plant. At an industry conference in Boston last week, Lee Sang-wan, president of Samsung's LCD business, recalled that such large LCD TVs were inconceivable five years ago. "Size should no longer be considered an issue for LCD TVs," he told the Society of Information Display.

But at the same conference, other engineers declared that the 10th generation of plants and glass sheets is likely to be the last. That glass will be 10.8 square meters, too large to be carried by oceangoing cargo containers and airplanes. Only low-bed trailer trucks could transport it, meaning the plants that make them would have to be built within driving distance of the factories where the glass is turned into a flat panel for TVs.

The alternative is to build a glass plant next to every LCD-panel plant.

But that is too costly for both glass manufacturers and panel companies, said Peter L. Bocko, vice president at Corning Inc., the largest maker of LCD glass.

Tenth-generation plants are likely to bring about affordable LCD TVs with screens that are 60 inches or more in size. But that may not be practical, engineers at last week's conference said, because such TVs would weigh about 100 pounds and require special equipment to move.

Samsung unveiled the world's largest liquid-crystal-display television in March. It is more than 80 inches wide.