"Haddad-land," an area where Israel contends there were frequent shooting and terrorist acts in the year before its bombing of Beirut, is territory in southern Lebanon controlled before the invasion by anti-Palestinian Lebanese. A reference to the area in Saturday's Post may have left the impression that the land is an Arab enclave in Israel.

As large-scale violence in Lebanon ended its second week yesterday, Secretary of State Alexander M. Haig Jr. and Israeli Prime Minister Menachem Begin met in New York to begin an intensive round of U.S.-Israeli negotiations.

There was no word of substantive achievement at the breakfast session, which was described by Haig afterward as preparatory to Monday's meeting of Begin and President Reagan at the White House. Official sources said Begin's stay in Washington has been extended to Tuesday to accommodate an additional meeting with Haig.

The agenda for next week's talks is long and difficult. The past two bloody and tumultuous weeks have created a new situation in Lebanon and sent shock waves through the Middle East, but the U.S. response to the Israeli stimulus remains highly uncertain.

Taking its direction primarily from Haig, who argued that any criticism would make Begin more intransigent, the administration has said almost nothing in public as Israeli forces rolled through Lebanon all the way to Beirut, far exceeding their initially announced objectives.

The silence has been taken as tacit approval in much of the world, especially the Arab world. Haig, according to some of those participating in closed meetings with him, has spoken at times of the advantages and opportunities the invasion brings. However, he and others have also spoken of the great dangers of stirring wider and deeper conflict.

U.S. officials have said repeatedly that the public silence did not imply inactivity, that Washington has been actively engaged with Israel in private since the start of the invasion. From all appearances, the confidential entreaties were only partly successful.

Begin did respond to Reagan's urgent letters from Europe last week with a cease-fire against Syria. Reagan's request did not come until after Israel accomplished its main Syrian-related military objective: destruction of the Syrian antiaircraft missiles in the Bekaa Valley.

The later cease-fire with the Palestine Liberation Organization, adopted after U.S. prodding, has been tenuous and less effective from the first. This is due in part to PLO noncompliance. But Israeli forces have continued to improve their military positions, placing increasing pressure on the Palestinian stronghold of Beirut.

Last Tuesday Washington sent a semi-public "signal" to Israel warning against an invasion of Beirut by suddenly describing next week's Reagan-Begin meeting as "tentative." Begin responded by declaring that he would not submit to pressure. At the same time, Israel renewed its assurances to Washington--originally conveyed several days earlier--that it had "no intention" of occupying Beirut.

Another U.S. action described as a signal of displeasure was the administration's decision to withhold action on the $2.5 billion sale to Israel of 75 additional F16 warplanes. A major reason for this, however, was the belief among many administration officials and some members of Congress that such action would court an emotional and unnecessary reaction overseas at a time when Israel is using its American weapons in Lebanon to powerful effect.

Chairman Charles H. Percy (R-Ill.) of the Senate Foreign Relations Committee has asked the administration for a new set of consultations with Congress before the F16 sale to Israel goes forward. Percy said yesterday he believes his request will be honored.

The main administration objective now is to restructure Lebanon by eliminating the Syrian presence and demilitarizing or eliminating the PLO, while building up the Lebanese central government. This is also Jerusalem's policy, and is one of its central conditions for withdrawal of Israeli forces.

Establishing order, legitimacy and a workable Lebanese authority is much easier said than done, as U.S. special envoy Philip C. Habib has learned to his repeated frustration in repeated trips to that war-torn country. Habib is trying again under the new circumstances of Israeli military occupation of southern Lebanon and the outskirts of Beirut, but the job seems to be proving as difficult as ever.

A crucial factor in ending the 1975-76 Lebanese civil war and establishing the July, 1981, Israeli-PLO cease-fire was the political and financial influence of Saudi Arabia. But Saudi cooperation and support may be more difficult this time.

According to Percy, who accompanied Vice President Bush and other prominent figures to Riyadh this week following the death of King Khalid, the Saudis believe the Palestinians kept their part of the bargain in the 11-month cease-fire, due in part to heavy pressure from Riyadh, but that Israel did not.

"They feel undercut by what has happened," Percy said.

According to U.N. reports, there was only one instance of shelling from Lebanon to Israel between last July and two weeks ago, when Israel began its bombing raids on Beirut. That incident was on May 9 and came in response to Israeli bombing and strafing of Palestinian positions that day.

The Israeli Embassy said there were at least 32 incidents of shooting and terrorist acts on the Israel-Lebanon front in that period, resulting in one Israeli death and one wounded, but most of this action was in Israel's "Haddad-land" Arab enclave.

Another central item for discussion with Begin is a U.N. or multinational peacekeeping force in most of southern Lebanon, which Israel has set as a price of its evacuation.

The Israelis would prefer a multinational force with a large American military component, as in the Sinai. The opposition on Capitol Hill to major American military participation is strong, however, and the administration is leaning toward an expanded U.N. peacekeeping presence.