That mild Moscow summit

One interesting thing about this week's Warsaw Pact meeting is that it was not a Warsaw Pact meeting. An institutional meeting of the Soviet empire's ''NATO'' never could have been whipped together like this summit conference of leaders of the Soviet bloc - or have brought forth such a brief informal statement. The question is what it all means beyond the impression of a relatively mild tone in contrast with recent Moscow rhetoric against US missiles in Europe.

To be sure, the bloc leaders broke no new ground in deployment policy. But, with a small unexpected phrase - in seeking ''at least'' an accord on reducing weapons - their statement conceivably implied something down the line. That phrase was not in the Warsaw Pact's institutional statement earlier this year, which otherwise said much the same.

It is known that the bloc as a whole would be difficult to enlist in the integrated countermeasures against US deployment as threatened by Moscow. Doubtless this, though conspicuously absent from the statement, was a topic of the summit. So too must have been the Polish situation, which likewise was not given public notice. And perhaps the MBFR, those mutual balanced force reduction talks on conventional weaponry that get overshadowed by the nuclear parleys?

The timing of the summit gave it the air of being partly a response to the West's Williamsburg summit and partly a prelude to talks between the Soviet and West German leaders, Mr. Andropov and Mr. Kohl. The muting of rhetoric is welcome whatever - well, almost whateverm - lies behind it. This much can be said. At least.