The Reagan administration, while publicly silent about the findings of the Israeli inquiry into the Beirut massacre, was watching closely yesterday to see whether it will lead to a break in the deadlock over withdrawal of Israeli forces from Lebanon.

U.S. officials, taking their lead from President Reagan, were careful in their public utterances to treat the matter as an internal Israeli affair. But leaders of the American Jewish community and several members of Congress hailed the independent commission's report as proof that the Jewish state is a viable democracy willing to engage in the most serious self-criticism.

Some American Jewish spokesmen also called for Prime Minister Menachem Begin to implement the recommendations of the commission, including the ouster of Defense Minister Ariel Sharon from the cabinet. The report charged Sharon with a heavy share of the blame for the killing of Palestinian civilians by Lebanese Christian militiamen last September.

U.S. officials are known to be especially interested in whether the report will force Sharon out of the Begin government or, at the least, lead to a pronounced weakening of the defense minister's power and influence.

In the U.S. view, Sharon, whom some administration officials privately describe as "almost a government within a government," has been the principal impediment to a Lebanon withdrawal agreement.

Some U.S. officials say they believe he has been working to cut the United States out of a major role in Lebanon and cause a de facto partition of that country that would bring the southern half under long-term Israeli domination.

At the same time, various officials cautioned yesterday that the removal of Sharon would not, by itself, automatically open the way to quick resolution of the Lebanon impasse and to progress on Reagan's broader Mideast peace initiative.

According to these officials, the real test will be whether the political reaction within Israel forces Begin--or any other alignment of forces that might come to the fore--onto the defensive in the Lebanon negotiations and lead the government to conclude that its best interests lie in swiftly ending the confrontation that began with last summer's invasion.

This, the officials cautioned, won't become clear for several days or even weeks. In fact, administration policy makers have been working on the assumption that one possible effect of the report will be an attempt by Begin to seek vindication of his Lebanon policies by precipitating new national elections. That probably would hold up progress toward U.S. Mideast goals for several months.

At the same time, though, the administration is positioning itself to exploit any openings that become apparent and, once the internal Israeli situation becomes clearer, to signal in increasingly tough terms that demands that the United States considers unreasonable could lead to a weakening of Israel's special relationship with this country.

In what some officials described as a deliberately calculated move, Reagan has become more outspoken in recent days about his irritation at Israel. In remarks Monday, the president said, "Israel is delaying, we believe unnecessarily. . . . " He also charged Israel with being "technically in the position of an occupying force" and said it was ignoring the "moral point" that the Lebanese government wants an end to Israeli occupation.

The officials said Reagan's special Middle East representative, Philip C. Habib, who returned to the region over the weekend, also had been instructed to reinforce the message of American impatience in unmistakable terms.

While Habib's current trip is not expected to break the deadlock, these officials said, the special envoy will be looking for resiliency in the Israeli and Lebanese bargaining positions as a preliminary to preparing a new U.S. proposal for withdrawal.

Wadi Haddad, a senior adviser to Lebanese President Amin Gemeyal, yesterday completed a visit here that included talks with top officials about expanding the size and role of the multinational force in Lebanon if Israeli and Syrian forces are withdrawn.

The Lebanese are understood to be seeking an increase in the force from its current strength of roughly 4,300 men--which includes 1,200 American Marines in Beirut and an additional 600 stationed offshore--to approximately 25,000. The Lebanese request reportedly calls for increasing the number of Marines to 5,000, with the rest contributed by other countries.

Although the administration has been wary of committing itself publicly, Haddad is understood to have received a tentative indication that the Marine contingent will be increased to roughly the level requested by Gemeyal if Lebanon makes progress in preparing its army to replace the multinational force.

Reagan gave the clearest signal to date of the U.S. position in his remarks Monday.

Referring to a withdrawal agreement, he said, "I personally have believed that if this requires even an increase in the multinational force for further stability, that we should be willing to do that."

Among American Jewish leaders who spoke out yesterday was Julius Berman, chairman of the Conference of Presidents of Major American Jewish Organizations, who said he believed that Sharon would, "out of a sense of patriotism, offer his resignation as called for in the report."

Rabbi Alexander Schindler, a former conference chairman, said he was confident that Begin will heed the recommendations and will assure that "the failings are corrected."