Mr. Sharon steps down, but. . . .

Ariel Sharon is no longer Israel's minister of defense, but he remains in the Israeli Cabinet and, so far as can be determined from the outside, the policies which he served remain in full force.

The important thing about the above is that Mr. Sharon was an enthusiastic tool or instrument of a long-term expansionist policy. The condemnation of Mr. Sharon's own personal behavior by the special court of investigation touched him , but it did not touch the policy. The commission's findings said, in effect, that it was wrong of him to send Phalangist militiamen into camps full of refugee Palestinians. But it did not say that it had been wrong to send the Israeli Army into Lebanon.

So it is no longer possible for Mr. Sharon himself to order Arab militias supported by the Israeli Army to go into Palestinian refugee camps. But nothing has yet tempered or obstructed the broad plan for the expansion of the power and range of the state of Israel which has been the obvious purpose of Menachem Begin since he became Israel's prime minister.

Thus the issue which is increasingly straining the relations between Washington and Tel Aviv is untouched by the findings of the special tribunal.

That issue has always arisen out of the desire of the government of the United States, pursued consistently from 1967 to the present, to have Israel withdraw within the basic frontiers which were recognized and accepted by the world at large previous to the 1967 war and to make peace with its Arab neighbors from within those frontiers.

That was the meaning of UN Resolution 242. It was the meaning of Camp David. It is the meaning of President Ronald Reagan's rephrasing of Camp David in the form of his ''peace plan'' of last Sept. 1.

It was also the declared intent of the government of Israel until Mr. Begin took over. His predecessors may have surreptitiously allowed the founding and gradual development of settlements for Israeli Jews in the occupied territories. But the policy was not officially avowed. A number of settlements were actually taken down by the Israeli Army.

Former President Jimmy Carter thought that he had extracted a promise from Mr. Begin at Camp David to recognize and accept the principle of Israeli withdrawal from occupied territories. Mr. Carter says that he had a clear promise from Mr. Begin to stop planting settlements in the West Bank. But Mr. Begin now denies that he ever agreed to suspend the settlements program for more than a short period.

The special court of inquiry into the Sabra and Shatila massacres handed down its verdict against Mr. Sharon on Feb. 8. It is particularly interesting in retrospect that four days earlier, on Feb. 4, Thomas A. Dine, executive director of the American Israel Public Affairs Committee, the leading pro-Israel lobbying organization in the US, gave a briefing to congressional staff members on Capitol Hill.

The burden of Mr. Dine's briefing was that Israel may find itself forced to keep its troops in Lebanon for years to come, and that Washington should give up trying to persuade it to do otherwise.

A formal version of Mr. Dine's view was printed in the Washington Post on Feb. 13. In that version he takes the line that ''Israel's air force and navy are the dominant forces in the Eastern Mediterranean,'' that Israel served American interests because it ''has driven two Soviet clients - the PLO and the Syrians - out of a major Arab capital and saved Lebanon for the US and the West, '' hence, the argument goes, Washington should back off from any ''pressure'' on Israel and should instead treat Israel as America's only reliable ally in the Middle East.

If Mr. Dine's advice were followed, the effect would be to allow Mr. Begin to proceed with the partitioning of Lebanon and the annexation of the occupied territories; the US would cease from providing modern weapons to Jordan and Saudi Arabia; and the US would rely on Israel alone to keep the Soviets out of the Middle East.

It is a prescription for abandoning UN 242, Camp David, and the Reagan peace plan of Sept. 1. It would also leave no choice to present and future Arab targets of Israeli expansionism. They would have to turn to Moscow for help against Israel.

The immediately important fact is that Mr. Begin, having withdrawn Mr. Sharon from the ministry of defense, is pursuing as consistently and persistently as ever his own plan for Israel's territorial expansion. Mr. Sharon was not a policy, only one of several means to Mr. Begin's purposes.