UN debates invasion of Grenada

Dismay, bewilderment, sadness, and in a few cases anger. These are the feelings expressed by many diplomats here regarding the United States invasion of Grenada.

Criticism of the US move voiced privately by many representatives runs from mild to sharp. Mexico's ambassador, Porfirio Munoz-Ledo, the first speaker at a special session of the UN Security Council called by Nicaragua, denounced the invasion. Mexico, the main regional power in the area, was not consulted by the US, according to diplomatic sources.

Only a handful of diplomats support President Reagan's initiative. ''It was a matter of credibility. If the US cannot protect its own interests and those of its friends so close to home, who will believe that it is willing to do so far away from its borders?'' says an Asian diplomat.

Representatives from communist countries denounced or condemned ''the US unprovoked aggression.'' Cuba's ambassador, Raul Roa-Kouri, called the invasion ''imperialistic aggression.''

Meanwhile, the overwhelming ''middle UN'' (West European, Scandinavian, moderate Asian, African, and Latin American nations) takes the US to task for its action in sorrow, and ''because now it is the West which will be projecting the image of the big bully,'' as a Western ambassador puts it.

Many diplomats here are bothered by the following thoughts:

* The US may have violated the UN Charter and international law.

* The US action sidestepped the Organization of American States.

* The US seems to have stolen a leaf from the Brezhnev doctrine. (The Soviet Union ultimately decides who governs a country within its sphere of interest.) ''We would have hoped that the US is not the USSR,'' says a moderate third-world diplomat.

* The US once again seems to be acting like the world policeman.