There is a nasty impulse in our national discourse on the Arab-Israeli issue to proceed from an arguable defense of Israel and its policies to a gratuitous, indiscriminate slur on "Arabs," to think and speak of them collectively, to judge the many by the egregious excesses of the few.

A positive pro-Israel prejudice is understandable when it is in favor of a secure Jewish state as a moral obligation to a people to whom civilization owes a great debt, a democracy with shared values, a friend. It is also natural enough for this attachment to translate into a tolerance of one or another Israeli government action or policy that works against proclaimed U.S. interests (the Lebanese invasion, the West Bank settlements, opposition to the Reagan "peace initiative," distrust of the current delicate efforts to build upon Camp David's beginnings).

But those are issues that can theoretically be dealt with on their merits and on principle. The problem becomes more difficult to deal with when a double standard is introduced -- a mindlessly negative, anti-Arab prejudice that would not be tolerated if it were directed at Israelis or at Jews.

It is not so much a matter of a flaw in our national character. It comes down to a matter of familiarity, of understanding, of stereotypes in cartoons, on television and motion-picture screens and in the written word.

Scholars write of Arab "tribalism" and unsettled "nomadic" instincts. The suggestion is that "Arabs" are somehow incapable of statecraft or stable nationhood. They dress funny, carry guns. Sadat was an exception; Arafat is the rule. Easily, we accept the Israeli definition of every hostile act against Israeli occupation forces as "terrorism" and every imprisoned Shiite or PLO-connected Palestinian as a "terrorist."

The point is not that this is a conscious double standard. The point is that there is one. It is regularly expressed in Middle East grievances and positions we indulge or ignore, seek to understand or feel free to scorn.

We excuse an Israeli government for its rejection of U.S. peace proposals out of sympathy for its domestic political concerns. So Congress shouts its approval of billions of dollars of unconditional economic and military aid. Jordan's King Hussein, by contrast, is sent to the back of the bus, for all his hard efforts to promote the peace proclitical risk, until he meets not only ours but Israel's requirements as a negotiating partner.

The hostage crisis was illustrative. Allyn Conwell, the informal choice of the hostages as their spokesman, was unique among TWA 847's passengers for his firsthand familiarity with the Arab world, as a businessman based in Oman. For expressing his understanding of the Shiite side of the argument -- as emphatically distinct from the hijackers' acts -- he was pilloried by commentators as prejudiced by where he makes his money.

The newsletter circulated by the American Israeli Public Affairs Committee snidely suggested Conwell had "gone native" and cited approvingly his dismissal by columnist George F. Will as an "energetic collaborator." Consider the likely response to similar charges against an American doing business in Tel Aviv and proclaiming sympathy for Israel.

Others among the passengers who had anything nice to say about their captors or their treatment, or saw any symmetry between their plight and that of the Shiites in an Israeli prison, were psychoanalyzed as victims of the "Stockholm syndrome."

It was not just okay, but maybe even funny, to make sport of the Shiite faith -- as in "chicken-Shiite" or "when the Shiite hits the fan." What you don't know, you can't hurt, was apparently the rule for many. It was not a general rule. But the exceptions were enough in evidence to confirm that there is a double standard at work to the detriment of a balanced public perception of the Middle East -- and a balanced U.S. policy.

At the first show of disfavor of this or that Israeli government policy, a cry of "anti-Israel" goes up and the insinuation of "anti-Semitism" is not far behind. Never mind that it is quite literally the wrong word; Arabs as well as Jews are "Semites" by ethnic origin and by definition. It is enough to note that for bigotry applied to Arabs there is no comparable rebuke.