Key elements of Reagan's National Space Strategy

* Ensure routine, cost-effective access to space with the reusable shuttle. This space transportation system is considered a critical element in maintaining US space leadership. It is to become fully operational by Oct. 1, 1988, at which time the National Aeronautics and Space Administration (NASA) will begin charging commercial users full mission costs. The agency now charges It hopes to bring that cost down to around $100 million by 1988.

NASA and the Department of Defense are to spell out the steps needed to reach that operational status in a report due Nov. 30. They also are studying the kind of launch vehicles that might be needed after 1995, with a report due by Dec. 31 .

* Develop a permanently manned space station within a decade.

Although called a ''station,'' this will really be more of a operations and research center on orbit. It probably will be accompanied by free-flying, unmanned space factories and instrument-carrying platforms.

The station will have a threefold mission: to help develop commercial space activities; to service satellites and other spacecraft; and to act as a permanent laboratory for scientific and engineering research.

* Plan and implement a long-range civilian space program.

This will include encouraging more international participation in US scientific and commercial space projects. It also means identifying meaningful, long-term goals toward which the program should be working. These likely will include a return to the moon or a manned expedition to Mars in the 21st century.

To ensure that basic space science is not neglected, the plan must include ''a vigorous and balanced program of civil scientific research and exploration.'' To this end, the Office of Science and Technology Policy (i.e. the President's science adviser) is to work with NASA and other relevant agencies to recommend such a program by April 1, 1985.

* Foster growth of commercial space activities.

This means doing what the government can to encourage development of companies that provide unmanned launch services (and, eventually perhaps, even operate the space shuttle), that carry out manufacturing in space, operate Earth resource survey satellites, and that continue to expand in the communications satellite business.

The Department of Transportation has been given special responsibility to smooth the way for the new expendable launch vehicle companies, which represent the beginnings of a new mode of transportation that may one day rival that of the airlines.

* Ensure that the space program serves US national-security interests.

This means maintaining free access to space - an analogue of the freedom of the seas. It includes efforts to stem the flow of Western space technology to the Soviet Union without bogging down the new commercial space users in needlessly complex regulations.

Options for space arms control will be studied. But, at the same time, the Pentagon is to pursue possible military uses of space, including the so-called ''star wars'' space-based missile defense program.