The United States is watching with growing concern the unprecedented building of Soviet forces along the Polish border and the closing of certain frontier regions along the border. The United States has also taken note of Soviet references to alleged "anti-Socialist" forces within Poland. We know from postwar history that such allegations have sometimes preceded military intervention.
The United States continues to believe that the Polish people and authorities should be free to work out their internal difficulties without outside interference. The United States, as well as some Western governments, and also the Soviet Union, have pledged economic assistance to Poland in order to alleviate internal Polish difficulties. The United States has no interest in exploiting in any fashion the Polish difficulties for its political ends.
Foreign military intervention in Poland would have most negative consequences for East-West relations in general and U.S.-Soviet relations in particular. The Charter of the United Nations establishes the right of all states, both large and small, to exist free of foreign interference, regardless of ideology, alliances, or geographic location. I want all countries to know that the attitude and future policies of the United States toward the Soviet Union would be directly and very adversely affected by any Soviet use of force in Poland.
Jimmy Carter, Situation in Poland Statement by the President. Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/251226