Beirut — The broad outlines of United States strategy to piece together this fragmented country are becoming clearer. The outlines are evident even as representatives of Lebanon's warring factions continue to meet to strengthen and police the cease-fire.
In the wake of the cease-fire, US hopes appear to be based on four pillars:
* Encouraging formation of a government of national unity which will strengthen Lebanon internally through power-sharing reforms.
* Ensuring a period of calm during which the Lebanese Army can be bolstered sufficiently to extend its control to wider areas of the country.
* Calming Israeli security fears sufficiently (as a result of Syria's crackdown on Palestinian fighters in Lebanon and by the rebuilt Army), to encourage the Israelis to pull back its troops from southern Lebanon.
* Enticing the Syrians sufficiently with a Lebanese national unity government which is sensitive to Syria's interests so that Syria might no longer feel it necessary to retain 40,000 troops in north and east Lebanon.
But the US strategy is a high risk one and is based on some questionable premises which in unpredictable Lebanon cold prove shaky or fall apart.
No one in Lebanon would predict a high likelihood of major internal reforms within the foreseeable future. As of yet there is still no venue or date set for the proposed conference on national dialogue called for by the cease-fire accord. In addition, several proposed participants have already stated conditions for their attendance.
There is indeed a general recognition among all communities of the need for political reform. The current system is based on a 1943 pact which everyone admits is outmoded. Last week a meeting of senior Muslim leaders - Sunni, Shiite , and Druze - put together a general ten-point program for change which got favorable comments from Lebanese Maronite Christian leader Camille Chamoun.
But when it comes to the specifics, few expect real reform efforts would take place in weeks or even months.
Much faster might be the setting up of a national unity government containing leaders of all factions. Some Christian and Sunni leaders would prefer that such an enlarged Cabinet take on the slow process of reform, setting up committees and working groups, rather than a separate conference.
But the Christians are already upset at what some Christian leaders believe is a mistaken US intention to accept substantial Syrian influence - and even troop presence - in Lebanon at the expense of Christian interests. A controversy has been stirred by reports in the Lebanese and US press of remarks by a ''senior US official'' in Beirut on Monday that a Lebanese government sympathetic to Syrian interests might encourage the Syrians to pull back their troops.
Christian leaders scoff at the idea that such influence will encourage Syria to leave Lebanon. Their suspicions are only one of many serious hurdles facing such a conference, where opposition leaders want Syrian backing to pressure certain Christian leaders.
''We are going to resist American pressure,'' insisted former Lebanese President and Christian leader Chamoun in an interview. ''If we follow the suggestion of (special US envoy Robert) McFarlane that Lebanon is fundamental for the security of Syria, this means he is asking us to be a satellite of a Syria which is the satellite of the Soviets.''
Chamoun said the Christians could resist the US easier than they could resist Syria because one was a democracy and the second a dictatorship.
The senior Muslim leaders meeting last week - who did not include Druze opposition leader Walid Jumblatt or Shiite leader Nabih Berri - also indicated nervousness about Syrian hegemony. They stressed that Lebanon was ''free, sovereign, and independent.'' Observers said this was meant as a message to the Syrians.
Many observers here - both Muslim and Christian - believe Syria's interests in remaining in Lebanon outweigh for the time being any interest in leaving. Its presence has made it the center of attention and of Arab funding in the region, boosted its standing in the Arab world, drawn attention away from domestic problems of the Assad regime,and provided a base for 40,000 Syrian troops.
Better relations with the US can be useful to Syria, say analysts, to offset overdependence on the Soviet Union. On the other hand, senior US officials have indicated that the US does not intend to widen its regional peace intiative - the Reagan plan - to give Syria a wider role, or to launch any new campaign to pressure Israel to return the Syrian Golan Heights which Israel has annexed.
Informed analysts here see little incentive for the Syrians to pull back totally even if the government is more favorable. Syrian Foreign Minister Abdel Halim Khaddam, who will meet with US Secretary of State George Shultz today in New York, said last week that Syria would not leave Lebanon before Israeli troops withdrew totally and the May 17 Israeli-Lebanese accord was abrogated.
There are some indications that the US would accept a Syrian presence in Lebanon in return for Syrian acquiescence to a stable Lebanese government.