WASHINGTON - Black leaders are displaying a heightened concern this season about the environmental consequences of immigration-fueled population growth. But in two major gatherings in the capital, the talk is only of the consequences.

At the environmental braintrust of the Congressional Black Caucus Foundation's 21st Annual Legislative Weekend on September 13, the words population growth and immigration were not spoken. That was the case even though the most mentioned concern was air pollution caused by burgeoning numbers of automobiles. Asked privately about the omission, some suggested that population growth either isn't an environmental issue or is politically impossible to discuss.

In a prepared statement that typified the view of participants that blacks suffer the greatest harm from pollution, US Rep. Ronald V. Dellums, D-Calif., said I am outraged as I am made aware of how minorities suffer disproportionately from environ-mental pollutants such as poor air quality, lead poisoning and poor drinking water in our urban areas.

The chief culprit in air pollution now is the automobile, several speakers said. We have been successful in eliminating the majority of industrial emissions - meanwhile cars have proliferated.

It is clear the predominant problem is in the inner cities, said Joanne Underwood, president of the INFORM environmental research organization. She raised the troubling statistic that carbon monoxide now violates health standards in 43 cities, subjecting its victims to fatigue, headaches, and lack of attentiveness - a devastating blow to those inner city residents who are under-educated, under-employed, and under-skilled.

And the cure may sometimes be as painful as the disease for some people, indicated Sharon Morris, legislative officer of the South Coast Air Quality Management District (Los Angeles area). In order to accommodate the emissions of an ever-increasing fleet of automobiles - even after measures to curtail their use and to control their emissions still further - the government is going to have to crack down hard on small businesses over the rest of this decade, she said. That will force the closure of many firms and have a disproportionate impact on black owners and employees, she affirmed.

Asked afterward if leaders were considering limits on population growth as one option to lessen the impact on small businesses, Morris answered Oh my, no. We can't touch the idea of limiting population growth. It isn't politically allowable. She said all decisions about trying to clean the air take into account that continued high population growth is an essentially inevitable force.

Leaders at the braintrust session said they were expecting a major increase in ethnic environ-mentalism, especially after the boost of a National People of Color Environmental Leadership Summit in Washington, October 24-27.

The organizer is the Rev. Ben Chavis, head of the United Church of Christ's Commission for Racial Justice, and a long-time activist against environ-mental threats to ethnic communities. When asked about population concerns, Chavis said the only mention of population at the conference would be related to the changing ethnic demographics as reported by the recent census.

Neither he nor the conference will be dealing with population growth as an environmental factor, he said. Chavis, who is black, told the Congressional Caucus that environmental issues can be used to bring Hispanics, Native Americans, and to some extent Asians into a close working relationship with blacks that often is not possible on many other issues.