JIMMY CARTER was right on the mark when he said the forthcoming Senate vote to lift the Turkish arms embargo is the most important piece of foreign-affairs business the Congress has left in this session. It's really quite simple. If the embargo is lifted, diplomacy get's a chance to start healing the wounds in Cyprus, the rent in Turkish-Greek relations, the strain in Turkish-American and Greek-American relations, and NATO's whole sorry disarray in the eastern Mediterranean. If the embargo stays on, everything gets worse.

The argument has been cast in pro-Turkish and pro-Greek terms, but that is misleading. There is a great deal in it for both Turkey and Greece, and for both Turkish and Greek communities on Cyprus, if the stalemate signified by the embargo is broken. The United States has gone to considerable lengths to make that case, explaining the vista that a lifting of the embargo would open, removing the previous administration's pro-Turkish tilt in military aid, and supporting Greece's wish not to be muscled by Turkey in their Aegean Sea dispute. The administration has also labored, successfully, to induce the Turks to offer a new Cyprus position conducive to negotiations. Ankara's position is not yet what Athens and the Greek Cypriots want it to be. The way to improve it is by the talks that would surely follow a lifting of the embargo.

The Greek lobby is hanging tough. That has led Sen. George McGovern (D-S.D.) to offer an imaginative way out. Mr. McGovern can hardly be regarded as someone dominated by the strategic concerns that, for good reason, guide the views of many others who wish to end the embargo. He is sympathetic to the division and hardship on Cyprus. Mr. McGovern suggests lifting the embargo, while linking future Turkish-aid requests (including arms sales) to a presidential certification of good-faith diplomacy. His amendment is designed to eliminate the stigma that the embargo is for Turkey, but to retain a non-humiliating form of encouragement to the Turks to continue moderating their policy. The administration supports this approach.

Let us underline the essential point. The embargo was at its outset a well-meant, legally mandated protest against the use of American arms for the occupation of almost half of Cyprus. But experience has proven it to be destructive of the purpose it was meant to serve - reducing the occupation - and of much else. The embargo stands now simply as a hostile act against an ally, and one not in the slightest endorsed by any other NATO ally - except for Greece. The Senate should end it in the manner suggested by Mr. McGovern.