The Carter administration reported yesterday that Israel may have violated U.S. law by using American-supplied warplanes and artillery during recent raids in southern Lebanon.

The State Department finding, in response to an inquiry from Rep. Paul Findley (R-III.), marked the third time in 22 months that a report of a potential law violation by Israel was sent to Capitol Hill.

Findley announced that he has introuduced resolutions intended to stop five pending sales of artillery, tanks and other weapons because the United States lacks assurance that the additional weapons will not be used to bring death "needlessly to hundreds of innocent men, women and children."

Israel maintains that the raids into Lebanon are in self defense against terrorist targets, and thus are permitted under the 1952 agreement governing U.S. arms sales. The United States has not accepted this position.While warning Israel that it views this use of American military equipment seriously, the United States has taken no action to make an iron-clad finding that the law has been violated or to stop the flow of arms.

"We are continuing to watch this situation with seriousness and concern. Further action on our part will depend on the course of events and our assessment of them," said Secretary of State Cyrus R. Vance in a report on the latest findings.

Vance's letter went to Capitol Hill at a time when the Carter administration, on several other fronts, was seeking to ease growing political tension with Israel.

Vance, in a breakfast meeting with Sen. Richard Stone (D-Fla.), said the United States is prepared to veto a draft U.N. resolution suggested by Kuwait that calls for an independent Palestinian state and deplores Israeli occupation of Arab lands.

Stone quoted Vance as saying that the United States is not trying to negotiate its own revision of U.N. Resolution 242, the territory-for-peace bargain which has been the basis for Middle East peacemaking efforts.

Israel has expressed concern and some indignation over reports that the United States is encouraging a revised U.N. resolution, acceptable to the Palestine Liberation Organization, reaffirming Israel's right to exist.

Senior State Department officials continue to say, as they have for the past two years, that the United States will deal with PLO if it recognizes Israel's right to exist and accepts U.N. Resolution 242. Israel has declared that it will never deal with the PLO.

Stone quoted Vance as having said yesterday that indirect or "tantamount" recognition of Israel's right to exist by the PLO will not be sufficient to change the uu.S. stand. The PLO, according to U.S. sources, is suggesting that "an important opportunity for a shift" is at hand, but without making clear the details.

State Department spokesman Thomas Reston maintained, in the face of new charges from Israeli Foreign Minister Mosha Dayan, that there has been no shift in U.S. policy toward Israel. Reston took pains to deny charges that the U.S. need for petroleum from Saudi Arabia and other Arab lands is linked to current policymaking on a Middle East settlement.

In an attempt to clear the air with Israel, President Carter has invited Israeli Ambassador Ephraim Evron to the white House for a working lunch today. Last weekend both Carter and special Middle East negotiator Robert S. Strauss telephoned Israeli Prime Minister Menachem Begin as a gesture of reconciliation.

Strauss, in another bid to prevent a deterioration in relations, has advanced a planned Mideast trip to around August 20 rather than next month.

The report to Congress on Israel's possible misuse of U.S. weapons is likely to generate new controversy, thus cutting across the efforts to repair relations. State Department officials indicated that they had little choice but to make the report, in view of requirements of law, a congressional demand and persistent questions about the matter from reporters.

Vance's report specifically cited Israel's July 22 air strikes against Lebanon, reportedly the heaviest such attacks in recent months. The U.S. made Phantom jets rocketed and strafed coastal villages south of Beirut. The Lebanese state radio said at least 15 civilians were killed and 50 wounded.

Beirut radio reports said the Israeli warplanes hit five towns, some of which are inhabited by Palestinian refugees. The Israeli military spokesman said the targets were Palestinian "terrorist concentrations."

Vance's report also said that Israeli deployment of U.S.-supplied artillery in southern Lebanon may have violated American law. The self-propelled howitzers involved are of the same type as a new sale submitted to Congress in recent weeks under export control laws.