In a move that threatens to revive the national debate over Israel's aims and goals in Lebanon, former defense minister Ariel Sharon has stepped up his criticism of the policies of his successor in what is widely being interpreted here as a bid to regain political power in a new Israeli government.

Sharon's most public salvo was made in a speech to political supporters last night in which he asserted that gains made by Israel in Lebanon under his leadership have been squandered since he was replaced as defense minister by Moshe Arens.

According to reports in the Israeli press, Sharon told Likud bloc supporters:

"When I left office seven months ago the PLO Palestine Liberation Organization had been ousted from Beirut, their infrastructure had been smashed, Galilee had been saved, the Syrians and the PLO had been driven from the Chouf mountains. Now, when I am no longer at the center of decision making, the Syrians and the PLO and the Druze who collaborate with them are returning to places from which they were ousted. . . ."

According to a well-placed source, the simmering tension between the two men flared during a Cabinet meeting Sunday when Arens "reminded Sharon he is responsible for the Lebanese Christian Phalangists getting into the Chouf" during the Israeli drive on Beirut. That development is widely said to have inflamed the centuries-old sectarian rivalries in the area and to have contributed to the current Christian-Druze fighting.

Despite Sharon's criticism, Arens has remained cautious in his public statements. Sources close to him say he is waiting to determine the next moves of Syrian and Palestinian forces in Lebanon before considering possible Israeli countermeasures.

But the sources also emphasized that Israel does not intend to intervene in Lebanon to save the government of President Amin Gemayel, on which Sharon placed so much hope.

Sharon's criticisms could foreshadow a renewed national debate here over the goals and ambitions Israel set for itself when it invaded Lebanon more than a year ago--goals and ambitions that seem more distant than ever now that Syrian-backed Druze militiamen and, according to the Israelis and the Lebanese government, Palestinian guerrillas are gaining control of the Chouf region and posing a threat to Beirut.

Implicit in Sharon's remarks was not only criticism of Israel's pullback last week from the Chouf mountains and the outskirts of Beirut, but also the lack of an Israeli response to Druze gains against the Lebanese Christian forces that Sharon cultivated as allies of Israel.

The Israeli pullback was followed immediately by the current fighting in Lebanon. Israeli officials have warned Syrian and Palestinian forces against moving into the areas evacuated by the Israeli Army, but Israel has taken no steps to intervene.

In a radio interview tonight, Sharon said Israel should prepare to mount, alone if necessary, a "salvation operation" to rescue an estimated 25,000 to 30,000 Christians in the town of Deir Qamar who are surrounded by Druze forces. "I would prefer that it be done with the Americans, but even if not we have to prepare for that immediately and maybe those steps may prevent the need to do it," Sharon said.

A senior Defense Ministry official said Israel has made known to the United States its willingness to participate in an effort by the multinational force to evacuate the trapped Christians. But the official said this would require agreement by the Druze to allow the evacuation to take place and that Israel would not mount such an effort on its own.

In his latest public statements, Sharon appears to be trying to return to power in a new government headed by Foreign Minister Yitzhak Shamir and to position himself for a later direct succession struggle with Arens should a Shamir government not last long, as many here predict.

Last night Shamir and leaders of the other political parties that form the current governing coalition signed a new agreement, apparently clearing the way for Shamir to succeed retiring Prime Minister Menachem Begin. Sharon publicly supported Shamir as Begin's successor amid reports--denied by Shamir--that Sharon had been promised a more important position than the powerless job of minister-without-portfolio he has held since being forced to leave the Defense Ministry.

Arens, who succeeded Sharon after the former defense minister was severely criticized by the Israeli commission that investigated last year's massacre of Palestinian refugees in western Beirut, has sought to downplay Sharon's criticism. Israeli radio quoted him today as attributing it to a natural "human weakness" of anyone who sees his successor at work and believes "that he would have done this better."

However, the differences between the two men are not likely to be easily glossed over. They go to the heart of a debate over Israel's war aims in Lebanon that is still going on and is still troubling to Israelis.

When asked about the June 1982 invasion, Arens has always defended it as a step Israel had to take. No country, he says, could forever tolerate a heavily armed hostile force threatening one of its borders as the PLO guerrillas in south Lebanon did to northern Israel.

Arens' defense has always been of the original announced aims of the invasion--to drive the PLO out of southern Lebanon and create there a "security zone" as a buffer for northern Israel. That aim was widely supported by the Israeli public.

But Sharon, the architect of the invasion, had far more ambitious goals. He wanted to drive the PLO and Syrians out of all of Lebanon and see the installation in Beirut of a Christian government that would be dependent on Israel and would formally make peace with Israel.

The Israeli pullback, done under Arens' leadership, in effect returned Israel to its original war aims inside a security zone in south Lebanon.