Lebanese President Amin Gemayel, saying that he "will not succumb to Arab blackmail," has launched a wide-ranging offensive to secure domestic and international support for the U.S.-mediated agreement for an Israeli withdrawal from Lebanon.

Gemayel today met with ambassadors of the five permanent members of the U.N. Security Council and with Jordanian Foreign Minister Marwan Qasem to seek support for the draft accord. He already has embarked on a campaign to secure a broad national consensus in this fractious country on behalf of the agreement.

In a fresh sign of the tensions arising from the presence of Israeli, Syrian and Palestinian forces in Lebanon, Lebanese radio reports said that Syrian forces fired at an unmanned Israeli reconnaissance aircraft and shelled Israeli positions in eastern Lebanon.

Israeli military officials denied that the attacks had taken place, but the reports underlined the jittery mood here. A commentary on state-controlled Syrian radio repeated previous warnings that war with Israel was possible, saying that Syria had decided to repel dangers not only from its own borders but also from inside Lebanese territory. Israeli aggression would lead to "unlimited war," the commentary said.

Sporadic fighting continued between Christian Phalangist and Moslem Druze militiamen in the hills overlooking Beirut. Israeli soldiers intervened to prevent artillery duels from spreading to the capital as they did last week.

Police said that two explosions rocked central and southern Beirut Tuesday night, injuring at least two people, Reuter reported.

Gemayel began his diplomatic campaign a day after Syria and the Palestine Liberation Organization publicly condemned the Lebanese-Israeli agreement. The rejections threatened to derail the accord, because Israel has said that it will not withdraw its troops from Lebanon unless Syria and the PLO also pull out.

Neither Gemayel nor his key advisers has responded publicly to Syria's and the PLO's condemnations. But Gemayel's actions since tentative agreement with Israel was reached last week indicate that he is determined to appeal to both moderate Arab states and major world powers despite the opposition of rejectionist Arab nations.

Clearly expecting the sharp Syrian denunciation that was to come, Gemayel told a group of Kuwaiti editors on Friday that he anticipated a "fierce campaign" against the agreement, especially because it allowed some Israeli soldiers to remain in southern Lebanon as part of teams to inspect and supervise border security arrangements.

"We will not succumb to Arab blackmail, which could eventually lead to perpetual Israeli presence in southern Lebanon," Gemayel said. He added that it would be "naive of us to accept the presence of 50,000 Israeli occupation troops in order to refuse 50 Israeli observers as part of an international supervisions committee."

Lebanese officials have not commented on their future diplomatic strategy, but hopes appear to rest on the prospect that the United States and Saudi Arabia can turn the Syrians around, possibly by offering cash as an inducement.

Meanwhile, Gemayel has dispatched emissaries throughout Lebanon to the former presidents and prime ministers, local barons and heads of fiefdoms who wield power in the various small spheres of influence in this long-fractured country. Indications were that a vote by the 99-member Lebanese parliament on the peace agreement would be delayed until a broad measure of support was garnered.