The weekend massacre in Beirut has had a deep effect on normally pro-Israeli Britain.
''At best, incompetent,'' is how Foreign Secretary Francis Pym described Israel's role in the Lebanese crisis.
Mr. Pym insisted that a final judgment on events there must await facts, but he spoke of his ''horror'' at reports so far. European governments, he said, would continue to press their joint position that the rights of Palestinians must be ''fully taken into account'' in any Mideast settlement.
Britain had wanted Israeli and all other foreign forces to withdraw from Lebanon. It saw more United Nations observers in west Beirut as an important step in that direction. But Mr. Pym agreed that the United States, Italian, and French supervisory force may well have left Beirut too soon.
Britain, he said, would continue to support US moves to establish a genuine settlement and it would add to the @3 million already contributed in humanitarian aid to Lebanon.
Some here say one casualty of the massacre may be US hopes for a moderate Arab peace initiative. West European governments' position on the Mideast recognizes an Israeli right to security and respect for Palestinian rights.