In an issue of growing controversy in its ranks, one of the nation's leading environmental organizations is considering whether to throw its weight behind an effort to reduce immigration as part of a policy to stabilize U.S. population growth.

The Sierra Club last week launched a referendum on the subject, mailing ballots to its 550,000 members nationwide. It asked them to choose between reversing or maintaining a two-year-old decision by the club's board to "take no position" on U.S. immigration levels or policies.

The debate, which some have called a battle for the soul of the environmental movement, has become an increasingly nasty one, with activists on opposite sides of the question trading charges of racism and demagoguery. Other environmental organizations, as well as groups alarmed by U.S. population growth and those favoring immigration, are watching the referendum closely.

The dispute reflects a dilemma for environmentalists. Most view rapid population growth as a problem and want to see the U.S. growth rate level off. But for many, tackling immigration, a major component of current U.S. population increases, means getting embroiled in a highly charged issue with implications far beyond the environmental movement.

"Make no mistake: overpopulation is, without question, a fundamental cause of the world's ills," Carl Pope, the Sierra Club's executive director, said in a statement defending the board's "no-position" stand. "But these are fundamentally global problems; immigration is merely a local symptom."

Moreover, he said in a telephone interview, if the Sierra Club comes out in favor of reducing immigration levels, "we would be perceived as assisting people whose motivations are racist."

Such arguments are "a form of denial," countered Alan Kuper, a longtime Sierra Club member in Cleveland. "We can't remain silent in the face of endless rapid growth" in the U.S. population, which he said is degrading the environment and wiping out modest gains being made in other environmental areas.

"It's a question of being environmentally correct versus being politically correct," said Leon Kolankiewicz, a club member and population activist in the District.

According to the U.S. Census Bureau, immigration is the main impetus behind growth of the U.S. population, which now stands at 269 million. Combined, legal and illegal immigration amounts to about 1.2 million people a year, the Immigration and Naturalization Service estimates. When the U.S.-born children of recent immigrants are included in the equation, immigration accounts for more than half of today's population growth, the Census Bureau says.

Largely because of the high fertility rates of immigrant women, the bureau in 1992 sharply revised its projections of the population by the middle of the next century. Instead of leveling off at about 300 million, it said, the population is likely to reach nearly 400 million by 2050 and keep growing. Population activists contend that those estimates are conservative because they are based on immigration levels significantly lower than the current numbers. The U.S. population is more likely to top 500 million by the middle of the next century, they say. They insist that this growth is what worries them, not the national origin or ethnicity of immigrants.

Backers of the Sierra Club board's position argue that since most immigrants these days are "people of color," mainly Hispanics and Asians, the issues of immigration numbers and ethnicity cannot be separated.

The ballots are due back by April 18.

The controversy surfaced in February 1996 when, in the midst of a contentious debate in Congress over a major immigration bill, the Sierra Club's board resolved to "take no position on immigration levels or on policies governing immigration into the United States." Ultimately, provisions to reduce legal immigration, which accounts for the bulk of the immigrant influx, were stripped from the legislation.

To population activists, the board's resolution did constitute a position, one that reversed long-standing Sierra Club policy of promoting the "stabilization" of the U.S. population.

The activists gathered 2,000 signatures on petitions to put the resolution to a clubwide vote and call for "a comprehensive population policy" that advocates ending U.S. population growth through birth control and "reduction in net immigration." However, the board refused to allow a yes or no vote on the measure alone. Instead, it added an "alternative B" proposal that affirms the 1996 stand and calls for addressing "the root causes of global population problems."

What is now called "alternative A" does not specify any immigration level. It has been endorsed by a variety of conservationists, including Lester Brown, co-founder of the Worldwatch Institute; E.O. Wilson, a Harvard biologist; and Gaylord Nelson, a former Wisconsin senator and founder of Earth Day. Alternative B has the backing of the Sierra Club board, nine former club presidents and a number of chapters across the country.

In arguing against alternative A, club leaders charged in a statement mailed to members that the proposal's supporters include "extremists acting from racial prejudice." It named California's Republican governor, Pete Wilson, and former Ku Klux Klan leader David Duke, whose World Wide Web page it said links environmental protection with "stopping illegal immigration and almost all legal immigration into America."

Richard A. Koris, a backer of alternative A in the District, called such arguments "demagoguery." During a recent appearance at the Great Falls chapter of the club, he and Kolankiewicz were shouted down as KKK members. "Whenever you mention the topic of immigration restriction," he complained, "{opponents} basically call you a racist."