This was the week when it became uncomfortably clear in Washington that the problem of United States Marines in Lebanon may require seeking a solution in Moscow.
The problem is that political pressures are mounting to untangle the Marines from the internecine warfare in Lebanon. President Reagan wants them out as much as anyone else. But he wants them to come out ''with honor'' and as part of a general pacification process which could be called a success for US intervention.
There is no general pacification process under way. The reason was recognized in the letter President Reagan sent to Capitol Hill on the subject Monday. In the letter he said that ''there is no question about the complicating role of the Soviet Union and Syria.'' He said President Amin Gemayel of Lebanon could have had ''national reconciliation already,'' but ''on Syria's terms.''
That is precisely the situation. American diplomacy worked out a Lebanese settlement plan last year on other terms. The May 17 agreement which US Secretary of State George Shultz negotiated between the Gemayel regime in Lebanon and Israel provided for the reconstitution of an independent Lebanon on terms favorable to Israel. In effect Israel would have become the principal outside influence in Lebanon.
Syria vetoed that agreement by refusing to have any part in it, and by refusing to withdraw its forces from Lebanon until the May 17 agreement had first been wiped out and Israeli forces withdrawn from all of Lebanon. Syria was able to make good its veto because Syria is backed by Moscow in the form of the latest Soviet weapons, manned by some 7,000 or 8,000 Soviet troops.
Syria wants a Lebanon settlement on Syria's terms, which means a Lebanon in which Syria, not Israel, is the major outside influence. If Mr. Gemayel wants to get control of all of Lebanon, he can have it - but only if he accepts it from Syria, not Israel.