AT times, public thought can appear beset by an excruciating compression. This can take the forms of racism, hatred, and alienation.It may well be, however, that these reflect a more basic, underlying evil: an impulse to expunge individual expression, to deny distinct diversity in the human race. It does this by castigating whole groups - blacks, Jews, women, homosexuals - as inferior, unfit, or conspiring. It can appear reasonable, can base its position on "scientific" study, on apparent incidents, or on a climate of unrest whose precise nature remains unclear. The heat of summer, joblessness due to economic recession and limited ed ucation, national politics, and international affairs involving the Middle East - such unconnected elements can seem to pile onto one another to produce an unstable climate. The natural conditions of public thought, like individual thought, are brotherhood, sisterhood, peaceableness, and acceptance. The flashpoint reached during the 1960s in America, when city after city erupted in tension and riots, need not be returned to in the '90s. Nonetheless, today's climate of volatility should not be dismissed as so many isolated incidents, as if such incidents do not aggregate into a prevailing mood. The Senate has begun hearings on the contentious nomination of Clarence Thomas, a conservative black, to the Supreme Court. Brooklyn's Crown Heights has been agitated the past month, after an automobile driven by a Hasidic Jew struck and killed a black child. Blacks "retaliated" by killing a Hasidic student. The city administration, headed by Mayor David Dinkins, who is black, has found it hard to get a dialogue going with a black community even more alienated than that of the '60s. In Detroit and Milwaukee, school officials are trying to establish "male academies" as one solution to the appalling problems - unemployment, prison - haunting young African-American males. The courts, so far, have insisted the schools also enroll girls. This past week a Stanford Medical School neurosurgeon, a woman, who had quit the Stanford faculty in June over long-standing sexism, decided to return, apparently after the prospect of a leadership change in her department. Dr. Leonard Jeffries Jr., black studies chairman at City College of New York, theorized in July that Jews and organized crime conspired against blacks in Hollywood. Last week a federal judge upheld the right of another City College professor, Dr. Michael Levin, on grounds of free speech and due process, to teach that blacks are intellectually inferior to whites. A hate publication that came through the mails to my desk one recent morning claimed Robert Strauss was "nominated as ambassador to the Soviet Union by jew-dupe George Bush ... to consolidate international jewry's 'New World Order. References to blacks and homosexuals were just as despicable. All this works in the background while the Bush administration attempts to forestall loan guarantees that Israel needs for the resettling of hundreds of thousands of Soviet Jews arriving in Israel. For Israel, the drawing together of Jewry dispersed for centuries is a profound wish. The Bush administration is trying to promote a Middle East pact - likewise a profound wish of Palestinians and a diplomatic objective of most of the West. Alienation has deepened as individuals have felt abandoned by public institutions. Since the 1980 election of Ronald Reagan, the cities, minorities, the schools, and public services have seen one government support after another chipped away. That there are women neurosurgeons, black black-studies chairmen, academic freedom protection even for obnoxious views, and the prospect for a gathering of the Jewish diaspora, are hardly negative phenomena. But reactions to unrelated matters can be piled together to create a dangerous public chemistry. If racism, sexism remained mere abstractions, they wouldn't matter. But they lead to attacks on individuals, and on groups of individuals. They must be uprooted and exposed. Those arguing for values that bind the local and world community must make a stronger case.