IT was in high school that I first realized that anyone, even one's supposedly Christian friends, can be bigots. For the first time, I was attending a Catholic school, and most of the boys there were white suburbanites who knew Blacks only from watching the Jeffersons.

I have lived in a racially-mixed neighborhood since 1973. By fourth grade, several of my closest friends were Black. Almost every week, I heard a racial slur in high school, with other students invariably joking about the appearance or the alleged "stupidity" of Blacks. When and if the headmaster found out about such incidents, he would give us a lecture about how this sort of slur was a denial of human dignity. But few of my classmates paid any attention.

UNFORTUNATELY, a Church document decrying racism issued last week by the Vatican may be greeted by the same indifference on the part of the world's Catholics. A great tragedy of the modern Church is that Catholics tend to ignore entirely the words of the Pope without pausing to ask if he might say something worth listening to and thinking about.

To apply to oneself a creed of acceptance and toleration such as Christianity espouses carries some responsibility with it. The history of Christians' attitudes towards race is especially troubling, and the new Church statement clarifies and emphasizes many Catholic ideas denouncing racism.

Anti-semitism has also been a problem in the Church for more than a millenia. It has its roots in the belief of some Christians that the Jewish religion, while still valuable in its doctrines, has been replaced by the word of Christ, who claimed to be the messiah of the Jews but was rejected by their leaders.

Recognizing the widespread nature of anti-Semitism in modern society, the new Church document condemns it as "the most tragic form that racist ideology has assumed in our century." In an attempt to dispel the myth that the Catholic Church was supposedly complacent in the face of Nazi racism, the document notes that Popes Pius XI and Pius XII condemned Nazi anti-Semitism in four official statements between 1937 and 1942.

Reading excerpts of the document shows the value the modern Church places on the equal treatment of all peoples. By definition, the document says, governments should protect human rights; countries that practice "institutionaized racism" are therefore illegitimate.

The statement, which is not a papal encyclical but simply an advisory document put out by the Church's Pontifical Commission on Peace and Justice at the Pope's request, condemns South Africa by name for its apartheid system. It also calls on the South African regime to overcome the prejudices which motivate it so it may "build the future on the principle of the equal dignity of every person."

In contrast to South Africa, the Church document cites the United States as a place where society has "found increased vitality in the melting pot cultures." But the document also points to latent racial tensions in American society that express themselves when "exaggerated nationalism" degenerates into "xenophobia or even racial hatred."

THE Church's warnings on racism in the United States are timely and well-founded. Unfortunately, however, they seem unlikely to be heeded. American Catholics are still just as likely as non-Catholics to fear other races and cultures unreasonably.

The influx of Central American refugees fleeing war-torn El Salvador and Nicaragua and economically-crippled Mexico has generated just as much mistrust and fear from Catholics as from any other group. Although Church social teaching says that when a country cannot provide the basic necessities of life, its citizens should be free to emigrate to those countries that can, Catholics have been as reluctant as other religious groups to denounce restrictions on emigration from Central America.

Another example of Catholics' reluctance to follow Church teaching is seen in their reaction, or lack thereof, to the January decision by the Reagan Administration to restrict the number of Southeast Asian refugees allowed into the country. It's no coincidence that this policy shift comes amidst nationalist cries over the "Yellow Peril" in education, real estate ownership and economic competitiveness. If American Catholics were to recognize that every-one deserves an equal chance at the freedoms and opportunities that the United States can provide, pressure against such a policy would be enormous.

In the case of racial equality at least, the Church has provided the world with a statement which all concerned with human rights should heed. It's a pity that many Americans, Catholics in particular, aren't listening.