Why Reagan plan falls or rises on troop withdrawal talks

There is a hidden agenda beneath the surface of the Israel-Lebanon talks which goes beyond a negotiated withdrawal of Israeli troops or future Israel-Lebanon relations.

It's an agenda that could determine peace prospects for the whole Middle East.

As diplomats from Israel, Lebanon and the United States sat down Tuesday to begin the series of negotiations, all sides were well aware that Arab moderates, specifically Jordan, will be closely monitoring the progress or lack of progress in the talks. This is because the moderate Arabs will decide whether to enter into broader talks on a US-proposed solution to the Palestinian and West Bank problems based largely on how quickly and successfully the Lebanon negotiations are concluded.

Should the Israel-Lebanon talks drag on, or if Israeli - and other foreign troop - withdrawals from Lebanon bog down, the Reagan Mideast peace plan is likely to fail as well.

On the other hand, the parties are also well aware that the Reagan plan - which calls for return of occupied West Bank land to Arab sovereignty in the context of a solution of the Palestinian problem - has been rejected by Israel. ''The state of Israel. . . will not accept a Mideast peace on American conditions, but only on its own,'' predicted columnist Roger Gehchan on the front page of the independent Beirut daily L'Orient-Le Jour.

Many analysts here believe Israel will pose conditions which delay the talks in order to foreclose prospects for the Reagan plan. Speaking to Lebanese academics at the American University of Beirut, visiting former US National Security Adviser William Quandt predicted that Israel would ''keep negotiations with Lebanon as a centerpiece of Mideast diplomacy for six to nine months in order to keep emphasis from shifting to the (occupied) West Bank and Gaza.''

The venue for the negotiations was deceptively peaceful. It was held at a resort hotel in a southern Beirut suburb that was agreed on after Israel dropped insistence that talks be held in Jerusalem and Beirut proper. Lebanese leftist journalists mixed freely with Arabic-speaking Israeli counterparts.

The Lebanon Beach Hotel is the only hostelry on Beirut's south coast still fully intact after Israel's invasion last summer. And in the Shouf mountains visible from the hotel, heavy fighting has raged for weeks between Lebanese Christian and Druze militias seeking to establish an advantage before the talks began.

Moreover, even at the stage-setting meeting, tension underlay the polite verbal sparring. (Full-scale discussions are expected to begin Thursday in the northern Israeli town of Kiryat Shmona) The sparring highlighted the broad differences between the Israeli and Lebanese positions. Israel stressed normalization of relations and security while Lebanon focused on withdrawal of foreign forces:

* The Lebanese chief delegate, former foreign ministry official Antoine Fattal, said the basis of withdrawal arrangements with Israel should be the 1949 armistice agreements, a legalism which underscores Lebanon's desire to stress the military dimension of the negotiations so as not to antagonize the Arab world.

* Israeli chief delegate and Foreign Ministry Director General David Kimche, on the other hand, insisted the armistice agreements had been voided by Lebanese ''association'' with Arab armies during the 1967 Arab-Israeli war and by Lebanese agreements with the Palestine Liberation Organization to establish a ''state within a state'' from which its guerrillas attacked Israel over Lebanon's southern border.

Israel dropped its earlier insistence that Lebanon sign a formal peace treaty. This was done in recognition that Lebanon cannot afford to alienate itself from the Arab world as Egypt's President Sadat did several years earlier. But Mr. Kimche said the agreement Israel hoped to sign would be ''but a step away'' from a full, final, formal peace treaty. He said Israel's aims in the negotiations were ''both friendship and security.''

* The US, whose role has been downplayed by Israel and stressed by Lebanon, struck middle ground, stressing both Israel's legitimate security interests and Lebanon's entitlement to full sovereignty.

It is expected here that Lebanon will make substantial concessions to Israel. President Amin Gemayel is in an extremely delicate position. On one side he is under pressure from Christian right-wing militias to yield to Israel and to exert stronger Christian dominance over all Lebanon. He is pressed on the other side by representatives of Muslim factions - which comprise a majority of the country - and by Arab neighbors, on whom Lebanon depends for trade, to stop short of full peace.

Israeli Defense Minister Ariel Sharon claims to have worked out - without US knowledge - a three-page agreement, unsigned, with Lebanese officials (a claim officially denied by the Lebanese government).

The alleged document proposes a non-belligerency pact, open borders for trade and travel, and special security arrangements in the 45-kilometer zone north of the Israeli border. While Mr. Sharon said the Lebanese had ''shied away'' from the document, it probably represents concessions at least some factions within the Lebanese power structure are willing to make.

Mr. Gemayel needs quick progress in the negotiations in order to reestablish central government authority and halt renewed violence between Lebanese factions.