US committed to major role in rebuilding Lebanon

President Reagan has pledged wide-ranging support for President Amin Gemayel of Lebanon and for a major international aid effort aimed at rebuilding Mr. Gemayel's war-shattered nation.

A Reagan administration official said that by placing high-level American support behind Gemayel, the United States hopes to increase the prestige and credibility of the Lebanese government. It has been a government which in many ways existed only in name - and only in Beirut - while foreign forces roved freely through Lebanon.

But some officials saw a sign of hope in the simple fact that in this time of difficulty for his nation, instead of developing a ''bunker mentality,'' the dapper, youthful-looking Gemayel was able to come to Washington. He met with President Reagan at the White House Oct. 19 over breakfast, and in additional talks which covered the questions of foreign troop withdrawals from Lebanon, the projected enlargement of the Lebanese Army, and economic reconstruction.

But a senior administration official made it clear that while the US was prepared to continue helping in all of these areas - through its negotiating efforts, through training for the Lebanese Army, and through economic and military aid - it was looking to other nations and to international institutions to play the key role in economic reconstruction.

In a briefing for reporters, the administration official did not say which other donors aside from the US and the World Bank were expected to contribute to such a reconstruction effort. But other officials indicated that the administration was looking to Western Europe and to Saudi Arabia to contribute in a major way. The Lebanese government has outlined needs which would require as much as $10 billion over the next several years.

Saudi Arabia can be expected to contribute considerable sums to Lebanon's reconstruction but only if the Lebanese continue to resist Israeli pressure for the signing of a peace treaty between Lebanon and Israel. The Israeli pressure has eased in recent weeks, but Israeli Prime Minister Menachem Begin has yet to give up the treaty idea.

Whatever international aid there may be, it is clear that President Gemayel now looks to the US as his main protector and guarantor. The Americans are acting as intermediaries among the Lebanese, the Israelis, and the Syrians in the search for a withdrawal of foreign forces. A US Defense Department survey team has returned from Lebanon to report on the Lebanese Army's training and military aid needs.

Gemayel's visit here was the first state visit to the United States by any Lebanese president. In the past, Lebanon's Maronite Christian leaders have often turned to France for protection, sympathy, and support, and the French are currently participating in both the United Nations' peacekeeping forces in the south of Lebanon and the multinational force (MFN) now in Beirut. From a Lebanese point of view, the US had often neglected Lebanon. But that time seems to have ended.

In his briefing for reporters on the Reagan-Gemayel meetings, the senior administration official said that the Lebanese leader had raised with Reagan the possibility of expanding the role and size of the MNF. Gemayel also expressed the hope that the MFN would stay on in Lebanon until the Israeli, Syrian, and Palestine Liberation Organization (PLO) forces are withdrawn from Lebanon. About 1,200 US marines are participating in the MFN alongside 1,300 French soldiers and 1,300 Italians.

According to the administration official, President Reagan did not commit himself to any expansion of the role of the Marines but remarked that he appreciated that the US troops had been so well received.

Special US envoy Morris Draper will return to the Middle East shortly to try to facilitate the withdrawal of foreign forces. Disagreements between Israel on the one hand and the US and Lebanon on the other as to the type of force which should secure the south of Lebanon have complicated the search for a solution to this problem.