When U.S. or Soviet astronauts arrive on the moon sometime in the 21st century to launch construction of permanent, manned lunar bases, they may find the Japanese already in residence.

Executives of Japan's major construction companies are already drawing up blueprints for their own space colonization efforts in the next century. Their longer-term plans envision orbiting space ports with hotels, restaurants, research laboratories, farms, offices, factories and even sports and amusement facilities.These executives apparently see big money available out among the stars, with expanding need for lunar homes, condominiums, hotels and vast agricultural plants.

Specialists employed by Hazami-Gumi Co. and Taisei Corp., two large-scale construction firms, are working on more fuel-efficient space launchers for shuttles that also would be capable of accommodating heavier rockets than those used today.

Engineers at Shimizu Corp., one of Japan's largest construction companies, are proceeding on the assumption that development of outer space stations eventually will create demand for first-class tourist accommodations.

The company has come up with plans for a $14 billion, 64-room, doughnut- shaped hotel. The facility would orbit the earth while rotating on its own axis every three minutes in order to create a gravity field similar to this planet's. Shimizu engineers see such a hotel as necessary for those visiting the moon before departing for Mars, their ultimate destination.

"One of the major benefits for engineers getting involved in space development is that it enables them to see things from a long-range view," said Shimizu's Shinju Matsumoto.

He added that he is certain "there is quite a good chance that sometime in the mid-21st century space will be a major leisure site." Mr. Matsumoto

went on to say that "although some new technologies will be necessary for constructing the space hotel, such as the know-how for creating artificial gravity, it is a fair bet that this will have been realized during the first half of the 21st century, once a clear goal has been set."

He conceded, however, that materials required for moon construction "must be light and flexible and much different from normal building materials available on the earth." For example, structures will have to be absolutely airtight, Mr. Matsumoto said. Because of extreme temperatures, insulation will be crucial to survival, and ways must be found to protect buildings from space debris.

At Ohbayashi Corp., another leading Japanese construction company, engineers have plans for setting up Moon City 2050. The center of this complex would be a 1,500-foot lunar tower with a sightseeing lounge featuring a view of the Earth.

Takao Saito, head of Ohbayashi's Space Research and Development Department, predicted that the company's moon base concept "will likely become a reality in the latter half of the coming century." He stressed, however, that "space development projects will be a lucrative business for construction companies even in the early part of the next century."

Ohbayashi already is involved in basic research, including work on designing a giant bubble capable of shielding green shrubbery, tiny forests and a small stream to provide the city's residents with an Earth-like environment.

Yoji Ishikawa, spokesman for the company's Space Project Department, notes that he expects the moon to provide the mineral resources required for construction of the city instead of having to import them from the Earth at great expense.

The company, he said, plans to use many lunar raw materials, since the moon rocks brought back by U.S. astronauts 20 years ago contain silicon, iron, titanium, aluminum and magnesium in abundance.

Not to be left behind, officials at Ishikawajima-Harima Heavy Industries have developed plans for setting up a food production plant on the moon. They are convinced that vegetables and grains can be grown in moon sand under artificial light and nurtured with special liquids containing calcium and potassium. They intend to use computers to monitor the crops, with harvesting to be performed by robots.