As the United States enters the second quarter-century of the space age, scientists, planners, and officials who carry out the nation's civilian space program share two major concerns.
They say they are disheartened by what they view as a continuing lack of well defined national goals for the program. And they express alarm at the possibility of a military takeover.
These twin themes permeated a symposium held by the National Academy of Sciences to commemorate Sputnik - the Soviet satellite whose appearance on Oct. 4, 1957, opened the space age. These themes also surface in conversation with officials and researchers of the National Aeronautics and Space Administration (NASA).
Twenty-five years after Sputnik, these scientists and officials say they believe that the US civilian space program is at a critical stage. They explain that lack of a well defined program plus increasing involvement of the military, with attendant secrecy, could compromise the gains made by that program as a technically successful, open activity which fosters international cooperation. At the same time they foresee an explosion in practical uses of space as Japan, Europe, the Soviet Union, and even some third world countries expand their own civilian space activity.
Harvey Brooks of Harvard University, a physicist and veteran science policy analyst, reminded the Academy symposium that the US civilian space program had been founded by law on a set of principles which, among other things, include:
* ''The separation of military and civilian space activities to the greatest degree feasible.''
* ''A high degree of openness . . . a strong emphasis on public information, and a willingness to expose mistakes as well as successes.''
* ''A strong international commitment. . . .''
Brooks noted that space is, by nature, an international ''commons.'' Many activities, such as world communications satellite networks, demand multinational cooperation. Also, the great cost of major exploration should be shared among nations, he said.
Yet, he warned, because America's civilian space program is drifting with no firm objectives, US ability to contribute to joint enterprises, let alone exert leadership, is declining. Moreover, he said, where military secrecy is injected into that program, it will poison the atmosphere for civilian cooperation with other nations. Paradoxically, he added, it may stimulate Western Europe, Japan, and others to strive even more vigorously for independent space leadership, to the economic detriment of the US.
NASA officials, speaking not for direct attribution, are blunt about their apprehensions. Concern over a perceived lack of a long-range, coherent space policy and of military interference permeates the agency from top to bottom.
For example, one highly placed official said that already such interference is quietly creeping in day by day, as more and more ''routine'' decisions have to be cleared with the Air Force and as formerly open facilities have to be partitioned for military secrecy. He said he is determined to resist this encroachment.
Another official said that a penchant for secrecy is already colliding with the legally-mandated NASA policy of openness with information. In one incident, a NASA official was reprimanded for handing around an article from the widely circulated magazine Aviation Week because it contained information about a military experiment on a space shuttle mission.
Both NASA officials and other critics of the militarization of the civilian space program say they recognize US military needs in space, especially for command of armed forces and reconnaissance. What they decry is what they term ''corruption'' of the civilian effort. Retired US Air Force Gen. Bernard A. Schriever reminded the symposium that the Air Force doesn't want such corruption either. It wants its own shuttles and its own space program which would be separate from, although coordinated with, that of NASA. NASA officials say that would be fine, but they note that there are no formal plans for a separate military effort.
Simon Ramo, one of the founders of the aerospace company TRW Inc., pointed out that, between them, Western Europe and Japan now have more engineers, and more money to put behind those engineers in specific projects, than does the US.