Cardinal William W. Baum has issued a pastoral letter denouncing racism as "heresy" and a "sin," and pledged "an increase in our struggle" against all forms of racial discrimination.

In the nine-page letter, the head of the Roman Catholic Archdiocese of Washington warned against a wide range of racially motivated behavior, from racist jokes to the failure to support programs of affirmative action. He suggests that parents should be as vigilant in guarding their young from racist attitudes as from "the effect of drugs, pornography and sexual immorality."

The cardinal issued a statement more than a year ago condeming the actions of the ku klux klan. But the document on racism is the first pastoral letter on a specific social problem issued by Baum in his six years as head of the church here. Other pastorals have tended to deal with more explicity religious subjects.

The Washington Archdiocese, which includes six neearby Maryland counties, has an organized and articulate black voice in the form of the Black Secretariat. It's estimated that about 75,000 of the nearly 400,000 Catholics in the archdiocese are black.

Baum's pastoral on racism, which mentions other racial and ethnic minorities as well as blacks, is in part a response to repeated requests from the Black Secretariat for such a statement from the cardinal.

The pastoral, which was dated June 22, was mailed Monday to the news media at the direction of Baum, who is in Rome, Copies eventually will be sent to all pastors. But because of its length, it will not be read from pulpits as has been the custom in the past, according to a diocesan spokesman. It will be published in the Catholic Standard.

Baum acknowledged efforts during past decades "to make racist behavior illegal." But in spite of these reforms, he continued, "the figures show a continuing pattern of misfortune for racial and ethnic minorities. Diminishing resources, limited employment opportunities and dwindling revenues affect them much more than others. Law enforcement procedures send a disproportionate number of them to jail. Victims of crime are disproportionately non-white and poor. Housing is still extremely difficult for them."