Japan's space program is ready for takeoff - and US takes notice

Japan is ready for a giant leap into space. The government's Space Activities Commission is revising space development guidelines established in 1978, now regarded as too modest.

One key element is the development of a domestically-designed rocket to carry a two-ton satellite into geostationary earth orbit by 1990. This launch capacity would be equal to the current level of the European Space Agency and not far short of the United States, officials say. Other objectives are the promotion of international space cooperation, including possible involvement in the US manned space station program, and development of Japan's own space shuttle, with a target of manned flights by the end of the century.

Recognition of Japan's increased stature in space is clear in an invitation from the US to get in on the ground floor of its proposed permanently manned space station project expected to be launched in 1992.

James M. Beggs, administrator of the US National Aeronautics and Space Agency , visited Tokyo last week to explain the $8 billion project and how the US visualizes possible Japanese participation. He offered a ''mere suggestion'' that Tokyo consider an initial financial investment of $750 million to $1.25 billion.

The official Japanese response was cautious. Government sources say Japan is interested, but worries about possible military implications of the space station that could create some political and diplomatic problems.

There is also the question of cash. The Japanese space program operates on a shoestring budget. It is uncertain how the public would view a major increase at a time when government spending is being slashed in other important areas like welfare and education.

But the Japanese are already committed to participating in the current space shuttle program. The National Space Development Agency (NASDA) is processing more than 500 applications from would-be male and female astronauts, one of whom will go aloft in 1988 to supervise various Japanese scientific experiments, particularly the manufacture of new materials in space.

While their program is very modest compared to those of the US and Soviet Union, the Japanese still believe they are making an important contribution - especially in discovering more about earth, other planets, and the strange physics of outer space.

''In purely scientific terms, we aren't very far behind (the US and Soviet Union),'' says Dr. Minoru Oda, an astrophysicist directing projects for the private Institute of Space and Aeronautical Science.

Japan has two space programs. The private space institute, with a 1983 budget of $67 million, puts up scientific satellites to gather data for astronomers and physicists. The government's NASDA, with six times the budget, primarily launches communications, navigation, and weather satellites.

Next year two Japanese satellites will blast off for a rendezvous with Halley's comet on its next regular (every 76 years) circuit through the solar system.

This is a cooperative project between Japan, the US, the Soviet Union, and Europe. Two Soviet probes will study the comet's physical makeup. One Japanese satellite will observe the high-energy plasma particles around it and measure its magnetic field, while a second will take ultraviolet pictures. A US probe will also be taking various measurements.

NASDA's success in placing communications and broadcast satellites into stationary earth orbit - a technique requiring a high degree of skill and technology - has encouraged it to expand its horizons.

Instead of developing a rocket to carry an 800-kilogram geostationary satellite, planners have decided to leap straight to a more powerful two-stage rocket with a two-ton lifting capacity.

Since their first launch of a ''pencil rocket'' 30 years ago, the Japanese have made rapid advances. Government and private industry, for example, are now forming two consortiums to work on an earth resources hunter satellite to be launched in 1990. Officials say it will feature a unique ''synthetic aperture radar'' that ignores cloud cover.

At the same time, the Institute of Space Science has completed the first prototype model of a ''space aircraft,'' a second generation space shuttle able to move freely between earth and space that does not need a rocket booster for launching.