CONGRESS HAD a jolly time this week bashing the Saudis. An administration proposal to sell missiles to Saudi Arabia was up, and both houses turned it down by margins so great as to raise a real question of whether President Reagan's certain veto will not be overridden. The Saudis, notwithstanding the sinister power sometimes imputed to their oil and "lobby," do not stand very tall on Capitol Hill even in good times. The collapse of oil prices, the faltering of peace initiatives in the Middle East and the current American focus on Libyan terrorism make these bad times. Israel and the American lobby for Israel held fire on the missile transaction, but Congress went ahead as though on autopilot.

Saudi Arabia, under its current management, is a friendly country. But the continued rule of the group now in power is not ordained for all time. Libya provides one example of an alternative leadership, Iran another. As between militant colonels and angry mullahs, the Saudi royal family looks pretty good. The Saudis often disappoint Americans, as Americans disappoint them, but like Americans they have a keen interest in a relatively steady Middle East linked closely -- though not too closely -- to the West. For the Saudis, open to a host of perils, defense is central. There lies the reason for American support of Saudi defense, by displays of constancy and the provision of arms. This is the connection that Congress would now casually break.

Congress observes that Saudi Arabia is an Arab country and that it offers support of one form or another to the PLO and to Libya. Congress should examine the implication of its effective position that all Arabs, whether they be designated moderate or radical, are alike under the skin, and are unreliable. This is a simplistic and self-defeating judgment with more than a touch of condescension to it. It writes off 20-odd countries, and invites radicals, fundamentalists and Russians to dominate a major region of the world.

Congress might wish to study what the Qaddafi regime said on Wednesday about the arms vote: "The U.S. administration dealt a severe blow again to the Arab rulers who pant after it and lick its boots at the doorsteps of the Black House. . . . This U.S. refusal constitutes a warning to the Arab rulers who have appointed themselves as guards of the U.S. and its interests in the region and an affirmation of the U.S. methods and arrogance in dealing with Arab rulers who have no shame, and who give in to its politics and who accept its successive insults."

President Reagan has promised to throw himself into the battle to save the arms sale. He has no choice. The United States must stay at least minimally engaged with friendly Arab states, especially at a moment when it is increasingly confronting unfriendly ones.