Mikki Mausu has landed and the situation is well in hand.

Mikki, who is better known to millions outside Japan as Mickey Mouse, has set up an entrepreneurial beachhead here on Tokyo Bay that, unlike countless other American efforts to export to Japan, has all the earmarks of success. It is Tokyo Disneyland, a $650 million amusement extravaganza designed to attract a new generation of affluent Japanese with an increasing yen for leisure.

When the park opens this Friday, a Japanese family will be able to ply the waters of 19th century America on a riverboat stern-wheeler called "The Mark Twain," glide through a haunted mansion packed to the rafters with robotic goblins, and duck a computerized cannonade on a voyage among a motley crew of Caribbean pirates.

The less adventurous can stroll along the colorful byways linking Fantasyland, Adventureland, Westernland and Tomorrowland, join in a singing jamboree of country-western bears or browse among the animated attractions, boutiques and snack bars that are closely patterned after the two Disney parks in the United States.

At a time when many American business people complain bitterly that Japanese red tape and cultural barbed-wire keep products from selling here, the Tokyo park's promoters expect the Disney magic to conjure up a ready market of 10 million visitors a year. A lot, of course, is riding on Mickey, Disney's charismatic mouse, as a super sales animal.

Millions of today's parents here huddled around television sets in the 1950s, wiggling the ears on their Mikki Mausu hats, during Disney's "Mickey Mouse Club" broadcasts. Many of them, promoters now say, will want to bring their own families on sentimental tours of Tokyo's Disneyland.

The sheer snob appeal of things foreign among younger, more internationally minded Japanese is also likely to provide a powerful attraction. Disney's animated films have long been hits here and Mickey Mouse tee-shirts and other trademark goods are popular with Japan's trendy teenyboppers.

The spires of Cinderella Castle sprout from the park's 201-acre landfill site on the north shore of Tokyo Bay, only about 30 minutes from downtown Tokyo by subway and bus. While the massive investment has raised eyebrows in Japan's no-nonsense financial community, promoters contend that the park means profit.

Within a 30-mile radius of Tokyo Disneyland live 35 million potential park-goers, more than three times the population clustered around the original Disneyland in Annaheim, Calif. Another drawing card may be the facility's wide-open spaces, In Japan, which is the size of California, many of the 117 million people live in cramped urban apartments about as large as the average American living room.

Nevertheless, the Magic Kingdom, Walt Disney Production's first venture outside the United States, has had its share of headaches. Access through Tokyo's snarled thoroughfares is expected to be a problem since a special express rail link will not be completed until the late 1980s and a freeway ramp adjacent to the park is behind schedule.

According to business analysts here, Oriental Land Co., Disney's Japanese partner, is believed to be on shaky financial turf because of its huge investment in the project, although its powerful backer, Mitsui Real Estate Development Co., and a consortium of Japanese banks are not likely to let it falter.

Even if the more than $200 million a year in revenues the park is expected to generate never fully materialize, however, Disney officials appear to have hit on a winning formula. The California-based company has not invested a single cent of its own, confining its role to planning, design, and technological know-how in manufacturing rides and attractions. In return, Disney will take a 10 percent cut of every admission ticket sold and skim 5 percent from the top of gross food-and-beverage sales.

"The Japanese," says Robert Mervine, a Disney spokesman, "are very finicky customers. They are used to having foreign products showcased to them and we think the park will satisfy their tastes, although it will be a while before we know."

Disney has added a few local flourishes, including a movie shown on a 360-degree screen with the aid of life-like robots that boils down 3,000 years of Japanese history into 18 minutes.

Conforming to Disney's Americanized ground rules, however, there will be nary a slice of sushi nor a bowl of noodles sold at any of the park's 27 restaurants. The hot dog and hamburger will take top billing. The o-bento, the traditional Japanese lunchbox that families here favor on outings, will also be banned. And, in keeping with Disney's well-scrubbed image, no sake or beer will be permitted on the premises.