The rapid deterioration of the situation in Lebanon in recent days urgently requires three kinds of prompt and careful response from the United States. The first step is to try to end the escalating violence. The US immediately should bring maximum pressure on Syria - and its backer, the Soviet Union - to try to get Muslim forces to cease their fire. The three other nations of the ''peacekeeping'' force, and the United Nations, also ought to make such efforts.
At the same time it is imperative that Christian Phalangist leader Amin Gemayel, if he is to survive as President, agree to share real governing power with the several Muslim sects. Thus far he has not, and this is a major part of the problem. The US should redouble its efforts to gain his acquiescence: The alternatives appear to be a new president, or else open civil warfare.
Despite the enormous challenges, an opportunity to improve the situation does exist. If the current violence were ended, and Gemayel did agree to share power, the crisis precipitated by the weekend resignation of the Cabinet could ultimately wind up producing a more stable situation.
Should all-out civil war occur, however, despite best efforts to prevent it, the US would need to be prepared in advance. Diplomatically it could not permit American troops to become more involved than they have already been on behalf of the Phalangist-led government.
Militarily it could not afford to have American troops trapped in Beirut with the prospect that it might be difficult to evacuate them safely.
Plans should be formulated immediately which, in case of need, would permit the safe removal of all US forces (and of those from the three other ''peacekeeping'' nations as well). Should the situation disintegrate to the point that the Gemayel government could no longer stand and there were no peace left to keep, then the US should immediately withdraw its forces. Not to do so would be to ratchet the risk to an unacceptable level.