THE ACCESSION of Greece to the European Economic Committee sharpens the question of what is meant by "Europe." To Constantine Karamanlis, the Greek politician most responsible for this consummation, Europe is an embodiment of the multinational democratic idea, a collective established to nourish a set of cultural values of which ancient Athens was a prime historical exemplar. Becoming prime minister after the colonels were deposed in 1974, Mr. Karamanlis felt thatt binding Greece to Europe ever more tightly, by any links available, was the best way to ensure democratic continuity. This is, by and large, the spirit in which most other Europeans seem to have treated Greek accession.

The other "Europe," broadly speaking, is simply the group of nations on the European continent that trade constantly and pervasively with each other within the EEC, or Common Market, a glorified customs union. Here trouble lurks, for Greece, more than any of the other nine members, though less than the likely next two, Spain and Portugal, is a relatively backward country in European terms. The sure shocks that accession will mean to Greek farmers, manufacturers and workers are already propelling the political debate within Greece. The other Europeans, too, can expect to be drawn increasingly into their own debate on what is to be gained and what is to be lost by bringing in the poorest, most recently authoritarian countries of Europe's Mediterranean littoral.

The Greeks, and the other Europeans, will have the sympathetic attention of many Americaqns as they work out these vexing questions. Actually, they will have more than the sympathetic attention. World War II revealed to all who could see the terrible potential of European nationalism. Since that time the United States, itself a federal nation, has been a committed supporter of the various federal arrangements by which Europeans put constraints on Germany and on the very notion of unchecked national power, and by which they have tended to their common security, welfare and prosperity.

Recently Greece has not only joined the Common Market as a full member but also rejoined the NATO military organization, which it quit in 1974 when Turkey invaded Cyprus. Difficulties remain -- difficulties always remain -- but it is a good turn for Greece, and for "Europe."