TOKYO (AP) _ American companies have trouble breaking into Japan's markets, according to the stereotype, because of everything from unfair trade barriers to finicky consumers.

But just the opposite has happened with American mail order catalogs _ Japanese shoppers are buying everything from L.L. Bean sportswear to Saks Fifth Avenue women's fashions.

These retailers are succeeding while other American businesses are still struggling because the merchants found a market where Japanese companies weren't fulfilling customer needs. Japan's own mail-order catalogs had been considered too stodgy.

Many middle- and upper-class consumers, especially the younger generation and city dwellers, have shunned Japanese catalogs for decades because of their hodgepodge mix of everything from cheap dresses and necklaces to diapers and dog food.

By contrast, some American catalogs offer high-quality merchandise carefully aimed at specific groups. And they often contain two other items unusual in Japan: a lifetime, no-questions-asked guarantee and pictures of top models.

Clothing with well-recognized U.S. labels also sells for much less in the catalogs than well-known Japanese fashions do in Japan's expensive department stores.

In other words, the American catalogs entered a market that contained overpriced fashions in the stores and inexpensive items in the bargain-basement Japanese catalogs.

``There was nothing in the middle,'' said Masayuki Kakio, an analyst at the Japan Direct Marketing Association. ``That's where the foreign mail order catalogs came right in.''

The U.S. catalogs usually offer their Japanese customers less selection than in America, but more and more of them are being translated into Japanese to make it easier to use them.

Distribution of the catalogs is easy in Japan, a country with as much direct mail as America and where many companies also rely on U.S.-style mailing list sellers. And products the catalogs mail to individuals don't require quality-control inspection in Japan.

The success of L.L. Bean, Lands' End, Patagonia and Eddie Bauer specialty catalogs also has prompted their owners to open retail outlets in Japan.

The new wave is represented by consumers such as Miho Takauji, an upper-middle-class working woman who has been hooked on such foreign catalogs for a few years. She often flips through them at her home in Tokyo and orders clothing for herself and her husband.

``In Japan, it's almost impossible to find anything good quality at a reasonable price,'' Takauji said. ``What I find in Japanese catalogs is cheap, but it looks cheap too.''

In just a few years, the foreign catalogs _ mostly from the United States and a few from Europe _ have won 5 percent of the $20 billion Japanese mail order catalog market.

``We haven't faced any obstacles. It was very easy coming into Japan,'' said Gary Steuck, president of Lands' End Japan.

Last year, L.L. Bean's estimated mail-order sales in Japan totaled nearly $200 million, or 80 percent of international sales for the outdoor-clothing company.

``Even with duty and shipping costs, we can still be useful to Japanese customers,'' said L.L. Bean spokeswoman Catharine Hartnett. ``Because people just can't find something comparable.''

The U.S. catalogs also arrived as their Japanese counterparts were undergoing a much larger challenge: an explosion of Japanese discount stores. Similar to Kmart and Wal-Mart, they have begun to lure customers away from the Japanese catalogs.

In fiscal 1995, several top Japanese catalog sellers had a combined operating loss of 2.4 billion yen, or $22 million, compared to an 11.4 billion yen, or $102 million, profit a year earlier.

By contrast, Lands' End last year opened a new warehouse, 3.5 times bigger than its first one, which it quickly outgrew.

``Sales growth by the foreign catalogs means less income for us,'' said Taeki Toshinori, an executive at Nissen Co., one of Japan's leading catalog and mail-order companies.

Yasuyuki Sasaki, a Nomura Research Institute analyst, said Japan's general sell-everything catalogs simply don't work now.

``A catalog cannot impress consumers just by the number of items or how cheap they all are,'' he said. ``Consumers are now interested in more specialized product lines.''