In the four-part series of front-page articles on ''The Red Army in Retreat'' {Nov. 18-21}, the Soviet military establishment is depicted as ''falling apart at the seams.'' Ironically, the weakening of our former Cold War opponent is and should be a matter of concern to us strategically.

What is at stake is the integrity of the Soviet command and control structure. The Soviet Union has had a fair share of sober, sane and sensible leaders. That the Cold War stayed cold is ample proof. Now that strategic leadership (both uniformed and civilian) is being tested anew.

Political and economic chaos plus morale problems among the troops could fragment and weaken the national security apparatus. First, that may put any imprudent adventurers and risk takers closer to the nuclear button. Second, it may create the climate that fosters the illusion that they have nothing to lose.

Militarily there is probably nothing we can do other than retain the credibility of our strategic forces in the hopes that there are those who continue to understand the logic of deterrence. A reasonable extension would be continued and expanded parallel arms reductions.

This assessment suggests that we have a stake in the political, economic and social welfare of the U.S.S.R. that transcends our concern for the success of the current regime. We have a keen interest in a stable Soviet Union.

CHARLES P. SHIRKEY Vienna

The writer was a staff analyst in the office of the secretary of defense from 1968 to 1970 and was a professor at the Naval War College from 1972 to 1976.