THE IMPASSE reached in the Carter-Begin talks last week laft Israel with one diplomatic card still to play: an attempt to induce Egypt to resume the direct negotiations President Anwar Sadat broke off in January. To that end, Defense Minister Ezer Weizman went to Cairo on Thursday. Mr. Sadat received him, to see what changes might have been wrought by the cold bath in Washington, and perhaps also to indicate a certain personal esteem for "Ezra." ,Mr. Weizman apparently did bring a few new verbal wrinkles, incuding a more explicit suggestion to grant West Bank Palestinians a role in negotiating the "self-rule" Israel offers them. But the changes were not sufficient to get peace talks back on the track. It appears that Israel played the Cairo card, and lost.

The immediate emotional effect in Israel was dismay. The more interesting question lies in the emerging political effect. As expected, Mr. Begin's rebuff in Washington led first his Cabinet and then the Parliament to declare confidence in his leadership. But the Israeli debate over how best to exploit the Sadat opening goes on. The prime minister faces open charges that he is losing Mr. Sadat. He is also accused of presiding over a grievous deterioration in Israel's relations with its principal patron, and thereby undercutting the country's negotiating position at the only moment in its history when negotiations have been at hand.

Israel has a possible alternative to diplomatic change. It isto try, by relying on American Jews and the othe (far more numerous) American friends of Israel, to change administration policy. Mr.Begin's scheduled trip to this country in May for Israel's 30th anniversary provides an occassion. We note here that there is nothing "wrong" with such an effort. Directly or indirectly, inany event regularly, the United States tries to leap over the heads of foreign governments. Israel's outreach is in that pattern and tradition.

But that leaves open the question of effectiveness. The administration has realized, we trust, the importance of avoiding the appearance that it is trying to dislodge Mr. Begin, rather than prompt a review of his diplomacy. The difference is not always easy to maintain, or detect, but it is crucial if the effort at influence is not to backfire. Similarly, the Israeli government must calculate whether a campaign aimed at American opinion would work. We think that, even in the American Jewish community, the Begin policies have cost Israel support.

American Jews, with the rigidity that is a luxury of distance, may not be as anxious about those policies as Israelis are, but the gap seems to be closing. So it is that Israel's political card, if fully played, may turn out not to be the sure and strong thing it was in the past.

Israel's third card is, of course, a review of its policy. It's proceeding. It may yet bring the Israelis to the point of considering a change of government but, regardless of that, it is Israel's best hand.