America's Middle East policy looks more than ever like a ''Lebanon first'' policy. The United States seems to have accepted the argument that the road to a comprehensive peace in the Mideast leads through Lebanon.
When President Reagan appointed Robert C. McFarlane, his deputy national security adviser, to become his chief Middle East envoy last Friday, he apparently intended to emphasize a new US determination to push for a full withdrawal of foreign troops from Lebanon.
Philip C. Habib, McFarlane's predecessor as chief Mideast negotiator, had run into an insurmountable problem with Syria, now regarded by the US as the main obstacle to a withdrawal of foreign troops from Lebanon. For a period of several months now, the Syrians have refused to deal with Mr. Habib. He was also coming under criticism from the Israelis, who charged that he was being less than evenhanded.
The low-key McFarlane, a retired Marine Corps colonel, could hardy be more different in personality from the blunt, energetic Habib. In a White House that has been lacking, at least at the highest levels, in defense and foreign-affairs expertise, McFarlane seemed to fill many gaps.
In working to gain support for Mr. Reagan's proposed MX missile deployment and nuclear arms control proposals, McFarlane impressed a number of Democratic congressmen with his detailed knowledge of the issues. He also succeeded in gaining their trust. It may have helped that McFarlane comes from a background of more than casual experience with Congress. His father served as a New Deal Democratic congressman from Texas.
Administration officials say that McFarlane must now try to ''restore momentum'' to the Mideast negotiations. One of his tasks will be to reassure Lebanese officials, who have placed great hope in the United States, that it will continue to work vigorously for a withdrawal of foreign troops. Some Lebanese fear that the US may place the issue on a ''back burner.''
Lebanon's president, Amin Gemayel, sought reassurances that this was not the case, during meetings with Reagan here last week.
Administration officials say they are now considering new approaches for McFarlane to take to the Mideast. But it is not yet clear, even to a number of highly placed Lebanese, what these new approaches might be. McFarlane's most difficult task will be to intensify the difficult dialogue with Syria, officials say. Both the Lebanese and Americans are concerned that Israel's planned partial pullback of troops in Lebanon will simply consolidate the de facto partition of the Mideast.
The focus on this and other Lebanese problems seemed to confirm that the administration is devoting its highest priority in the Mideast to Lebanon, with less attention being given to the Palestinian issue and the Israeli occupation of the Jordan River's West Bank.
The Syrians currently control more than a third of the territory of Lebanon. The Israelis also hold more than a third. That leaves less than a third to the government of Lebanon.
Some Lebanese officials suspect that the Syrians and Israelis, while not working directly in concert, have ''complementary interests'' in Lebanon. They doubt that the Syrians really want an Israeli withdrawal, and vice versa. The presence of enemy troops provides each side with a pretext for staying.
Lebanon, more than any other country, contains the basis for a wider peace or for a wider war, argues Ghassan Tueini, a top adviser to President Gemayel. America's credibility in the Middle East - as well as the credibility of negotiation with Israel - depends on the outcome of the Lebanese conflict, he says. ''What Lebanon has done is something very important,'' says Mr. Tueini, who is a former ambassador from Lebanon to the United Nations. ''Lebanon is considered to be the last country that would dare sit down with Israel across the negotiating table, with American participation, negotiate for months and months, and then reach an agreement, sign it, take it to Parliament, have it debated, and have it approved by near unanimity.''
''What we may be witnessing today is Lebanon being penalized for that,'' Tueini said in an interview, referring to Syria's opposition to the Israel-Lebanon agreement of May 27. ''If Lebanon gets away with that, then a basic change is occurring in the Middle East. If America is prevented from seeing to it that this leads to a successful conclusion, then what credibility is left to America? And how can we get other countries to accept this course of action?''
''Lebanon has proved over the years that it contained all the seeds of all the conflicts in the Middle East. The road to peace necessarily goes through the Lebanon.
''If war . . . by creeping confrontation between Israel and Syria is maintained in the Lebanon, then how can you ever make any progress anywhere else in the Middle East?''