By branding the 1990 civil rights act a ''quota bill,'' Mr. Bush has made it clear that he is not the president of all Americans. At a time of great racial division and misunderstanding, Mr. Bush resorts to race-baiting. As with the Willie Horton ads, which helped win him the presidency, Mr. Bush has again demonstrated his insensitivity toward black Americans and insulted every black American who believed that here was a man who could be their president too.

Mr. Bush could have refused to sign the bill because of the increased burden it would have placed on business. He could have argued that in a time when we want to put more Americans to work at better wages, a bill that would make it more expensive to do business is not in the best interest of the country.

The proposed act was designed to protect gays, religious minorities, ethnic minorities and racial minorities from job discrimination. It was designed to return to old legal standards and has as its principal advance an extension of remedies for women. To call it a ''quota bill'' is a lie. The act went so far as to say that it should not be construed to promote quotas. To call it a ''quota bill'' is to resort to David Duke-like demagoguery at a time when we need ''a kinder, gentler'' leadership.

The civil rights act of 1990 was an imperfect compromise; there were honorable reasons not to sign it. Mr. Bush touched on a few of those reasons in his veto message. But the continued use of the racial code word ''quota'' to justify his opposition is a slap in the face of every thinking American.

Perhaps Mr. Bush believes that rattling his saber at Saddam Hussein will distract Americans from his protect-the-rich and divide-the-poor strategies at home. He will find his chickens coming to roost in time for the 1992 elections. We will have another chance to elect a president for all Americans.

MARK LLOYD Washington