For over 25 years, despite frictions and tensions, Lebanon thrived and flourished--economically, culturally and politically. Before the PLO's arrival and the Syrian occupation, the Lebanese succeeded in maintaining exemplary stability. Even now, after all the fratricidal bloodshed, there is good reason to believe that, if left alone, they can pick up the pieces and reach a modus vivendi.

But Syrian President Hafez Assad will not leave them alone. While piously expressing concern for Lebanon's sovereignty, he is refusing even to discuss Syrian withdrawal. He is calling for the overthrow of the legitimate government in Beirut, with the obvious intention of replacing it with a puppet regime. He is using anti- government forces as proxies, helping them with materiel, logistic support and artillery. And he is trying, by inflicting ever-mounting casualties, to make the stay of the multinational force untenable. By now, even the most credulous Western observers are beginning to realize that Assad is not just jockeying for a position of influence, but pursuing a historic, unwavering Syrian ambition: the annexation of Lebanon.

Assad has never made a secret of his design on Lebanon. When his troops entered the country in 1976, he declared: "Historically Lebanon and Syria are one country." Throughout seven years of brutal occupation, official Syrian pronouncements stressed the permanence of the Syrian presence. Even after the Israeli advance forced a Syrian withdrawal from a third of the country, the Syrian foreign minister, Abdel Halim Khaddam, stuck to his guns. "Lebanon is a part of Syria," he declared. "We shall counter any attempt at separatism, we shall reclaim Lebanon, along with its mountains and its coastal areas." And as recently as June 20, Assad's information minister reiterated: "Lebanon and Syria are one people in one country."

To deflect Western opinion from his own aspirations, Assad repeatedly raises the specter of Israeli "expansionism." That his allegations find a sympathetic ear in the West is a sad commentary on the democracies' collective memory. It is now a little more than a year since the last Israeli soldier left the Sinai, thus sealing the forfeiture of 91 percent of the territory gained in the Six Day War. In giving up the Sinai, Israel relinquished not only strategic depth, vital naval and air bases and flourishing settlements, but oil wells and a wealth of other natural resources. These could have given Israel a favorable balance of trade and paved the way to economic independence. But Israel deemed even this a price worth paying for peace. Such sac- rifices are hardly characteristic of expansionism.

Assad is well aware of Israel's desire to leave Lebanon. His perception is that Israel will do nothing to thwart him, unless its own borders are threatened. He believes that the internal mood in the United States and Israel precludes their making sacrifices for Lebanon's integrity and sovereignty. And emboldened by SAM 5s, over 5,000 Soviet "advisers," a fully re-equipped army and Soviet political backing, he believes he can now begin realizing the dream of "Greater Syria," which includes not only Lebanon but also all of Mandatory Palestine (i.e., the territories of Israel and Jordan).

Assad's goal is all too compatible with the Soviet interest in dominating the Middle East. The SAM 5 network, hooked up with the Russian defense system, threatens every Western and pro-Western position in the region. The collapse of the pro-Western Lebanese government and the scuttling of the American-sponsored Lebanon-Israel agreement would be a crushing American defeat and a decisive Soviet victory.

Israel and the United States must realize that Israel's local security concerns and America's geopolitical interests coincide in Lebanon, and that a failure of nerve now may spell disaster in the future. Both countries should forget past disagreements on tactical steps and join in close strategic cooperation to counter the Syrian-Soviet onslaught in Lebanon. A firm demonstration of American resolve will strengthen the American position in the region, particularly among pro-American Arab regimes increasingly fearful of the Syrian-Soviet hegemony. It will also signal to the Soviets and the Syrians that Lebanon is not theirs for the picking.