If ever there were an institution that would appear to be impervious to the heat of America's immigrant melting pot, it is the sushi bar.

Every slice, every dice is steeped in elaborate Japanese ritual.

The rice must be molded with just the right amount of space between the grains. The fish must be presented according to rules of color and shape as exacting as those for a floral arrangement.

The true professional sushi chef, or itamae, is trained with the meticulousness of a brain surgeon. A year can be spent learning the technique for cutting the thin strips of daikon radish that accompany a sashimi platter, for example.

So particular is the sushi chef's art, so tied to the mother country is the 1,400-year evolution of the cuisine, that restaurants have imported the chefs since the first U.S. sushi bars opened in the 1960s.

But in the way that caviar was, well, overfished, so too have been sushi chefs.

Walk into any decent Washington area sushi bar, and -- although the chefs might greet you with the traditional welcoming cry of "Irashaimase!" -- there's a good chance the accent will be Hispanic, Chinese or Laotian.

At one of the District's oldest sushi restaurants, Sushi-Ko in Glover Park, only two of the eight full-time sushi chefs are Japanese. The rest hail from China, Vietnam, El Salvador, Honduras and Guatemala.

Tachibana in McLean employs a Laotian, a Vietnamese and a Salvadoran.

Tako Grill in Bethesda has sushi chefs from El Salvador, Honduras and Mexico.

From Arlington to Rockville, restaurant owners offer the same explanation: With new sushi bars sprouting like shiitake mushrooms and the wait to sponsor expert chefs from Japan growing ever longer, there simply aren't enough Japanese chefs to go around.

"We have four chefs in Japan waiting for the visa to come work for us. But these days, it can take up to five years, and they may change their minds or situations before then," said Terry Segawa, owner of Tako Grill and a founding member of the National Sushi Society. "So it's easier to find somebody here to train as a chef."

The challenge dates to the early 1990s, when a fascination with Japanese culture and a trend toward more healthful diets created a nationwide sushi craze, said Trevor Corson, author of a soon-to-be released narrative of sushi's evolution, "The Zen of Fish."

In 1995, there were a little more than 4,000 Japanese restaurants in the United States, according to Japanese Restaurant News, an industry monthly. By 2006, there were more than 9,000. At least 100 are in the Washington area.

Given the size and diversity of the region's foreign-born population, it is perhaps not surprising that Japanese restaurateurs have turned to other immigrants to help feed their customers. After all, the Washington area is a place where Korean grocers employ Salvadorans to stock their shelves and Indian doctors advertise their services in Spanish-language newspapers.

Still, the purists are out there.

"I tell people that we are not serving Japanese food. We are serving Japanese culture," said Yoshi Itoh, owner of Makoto in upper Northwest, one of the area's most traditional Japanese restaurants.

To Itoh, the thought of schooling a foreigner in the art of Japanese cuisine elicits a shudder.

"They just want to learn the skills; they want to take short cuts," said Itoh, a soft-spoken man of 62.

Itoh said he would not even consider teaching someone to prepare sushi until the student had spent at least four years mastering the intricacies of the centuries-old Japanese tea ceremony -- whose manners and aesthetic lie at the heart of all Japanese cooking. As for the sushi instruction itself, that requires at least four more years, Itoh said.

Once, Itoh said, he attempted to put a prospective chef from China through this training regimen. "It was not a success," he said dryly.

The Japanese Agriculture Ministry shares his concerns. Last fall, it announced plans to halt the "corruption" of Japanese cuisine by creating a certification system for overseas restaurants that claim to serve sushi and other Japanese food.

Fortunately, Itoh's restaurant is a tiny shoebox of a place that can survive with just two chefs -- himself and another Japanese man -- who would easily pass muster with the sushi police.

Owners of more than a dozen larger local sushi bars said they do not have that luxury. They have had to find ways to incorporate non-Japanese chefs at their counters without compromising the high standards of their trade.

At Sushi-Ko, Aki Nakamura, 37, the Japanese-born assistant to the head chef, said he has learned to adapt his speaking style when training Central Americans.

"We Japanese are very indirect," he said. "In Japan, you would never say, 'You must do this.' You would say, 'It will be better if you could do this.' "

But with the cultural disconnect and the broken English that is the restaurant's lingua franca, he said, "when I put it indirectly, there are lots of misunderstandings."

Among Nakamura's most avid students is Napoleon Mejia, 35, a farmer's son who came to Washington from his native Honduras when he was 16. A few years later, Mejia got his first taste of sushi when he took a job in the kitchen of Perrys restaurant in Adams Morgan.

"I had never tried anything like it -- never even imagined anything like it," Mejia said in Spanish. "But I loved it right away. The flavors are so fresh. And it's like an art form."

Intrigued, he persuaded the sushi chefs there to begin teaching him on the side. Within a year and a half, he had picked up enough skills to land a job behind the counter, then a gig making sushi for Whole Foods and, ultimately, the job at Sushi-Ko.

For Jose Calderon, 26, a Mexican-born chef who works at Tako Grill, sushi was more of an acquired taste.

"At first, I only liked California rolls. It took me a while to get used to the raw fish," said Calderon, who got his start washing dishes in a Mongolian restaurant at age 16.

Now, Tako Grill's owner, Segawa, considers Calderon so promising that he is planning to send him to Japan for a month of advanced training.

Kunio Yasutake, owner of Matuba in Arlington County, is even more unorthodox. Two years ago, he hired the daughter of a sushi bar owner in Japan to man his counter.

Female sushi chefs remain a rarity in Japan, where popular myth holds that a woman's hands are too warm to mold rice correctly.

"She said it was so hard for her in Japan," Yasutake said of the woman, who has since returned to Japan. "But here, she was our star."

Not all restaurateurs share Yasutake's confidence in non-traditional chefs.

One D.C. sushi bar popular with visiting Japanese businessmen has a special code that waitresses can write on the order ticket to ensure that dishes for Japanese customers are prepared by a Japanese chef rather than one of the restaurant's six Central American chefs.

"Our non-Japanese chefs are okay," said the manager, who asked that his restaurant not be named for fear of offending American customers, "for the United States."