The smokestack at the Asarco copper smelter in suburban Ruston, Wash., stands higher than the Washington Monument, forming the western edge of the Tacoma skyline. For some Tacoma residents, it's a symbol of the port city's industry; for others, it's a reminder of the plume of air pollution that usually blows toward the northeast, across the islands of Puget Sound.

This week, the Environmental Protection Agency unveiled new proposals to reduce the poisonous arsenic in the emissions from both the smokestack and the large copper converting machinery elsewhere in the 80-acre plant. The EPA's proposals are virtually identical to a regional air pollution control agency's existing requirements.

At the same time, the EPA asked Tacoma's residents to answer two questions:

* Are the proposed controls enough to reduce health risks to an acceptable level?

* If not, would the benefit of even lower health risks be worth the cost in jobs if the 87-year-old plant, which employs 570 people, shuts down?

"In making this proposal," Ernesta B. Barnes, the agency's northwest regional administrator, said in a prepared statement, "the EPA is openly acknowledging that our proposals . . . will not eliminate risks, but will only reduce them. The question facing citizens affected by Asarco emissions is whether the reduced health risk is acceptable."

EPA Administrator William D. Ruckelshaus "would like to see some kind of consensus from the community," said Bob Jacobson of the agency's Seattle office. "That can't be the determinant of the final decision, but if a consensus becomes manifest, it would help."

Between now and late August, when a public hearing on the proposals is scheduled, Jacobson said, the agency would be doing "aggressive outreach" to ensure that the public comment it receives is informed. The difference between this public hearing and others held by the agency over the years "is a difference only in degree," Jacobson said. "We're doing this more aggressively than in the past."

The reaction from one local environmentalist was outrage. "This is job blackmail," said Ruth Weiner, president of the local chapter of the Sierra Club and a professor of environmental studies at Western Washington University. "You're going to pit neighbor against neighbor, people who work for the plant against people who don't."

The question of jobs is a sensitive one to Pierce County, home of Ruckelshaus's former employer, the Weyerhaeuser Co. The unemployment rate is running above 13 percent and other industrial enterprises, including a Boeing Co. plant and some pulping operations, have been on a slide.

The future of the Asarco plant has long been considered precarious. In 1981, EPA economist Robert L. Coughlin predicted that a variety of economic factors probably would combine to force the plant to shut down within five years. The plant also is the only domestic producer of arsenic; some of its arsenic-rich ore comes from the Philippines, where a new government-subsidized smelter recently opened and may compete for the available ore.

In 1979, the Asarco plant's electrolytic converter closed, and employment since then has declined by about 300 people, according to plant manager Larry W. Lindquist.