A government scientist said Friday that a recent study of the impact of sulfur emissions from a coal-fired power plant in northern Arizona shows that the plant's emissions may significantly affect visibility in the Grand Canyon during the winter.

However, a spokeswoman with the Salt River Project, which operates the plant and conducted the $12.5 million study, said the study showed that sulfur emissions from the Navajo Generating Station in Page impaired visibility in the canyon only 4 to 7 percent of the time during the study period last winter.Page is located 16 miles east of the Grand Canyon National Park boundary.

Bill Malm, a research physicist with the National Park Service, said the agency did a $2 million study in 1987 of the impact on canyon haze from the power plant and found that it accounted for more than 50 percent of the loss of visibility in the park overall.

"We think it's pretty cut and dried at this point - when the conditions are right, both the studies show that it has a high impact on visibility," Malm said.

The SRP study was conducted during one of the best periods for visibility in the Grand Canyon, probably because the winds were blowing the plant emissions in the other direction, Malm said.

In addition, "NGS (Navajo Generating Station) is surrounded by Class I national parks. If it (the plant's emission) didn't go to the Grand Canyon, where did it go?" Malm queried.

SRP spokeswoman Teri Morris explained the differing analyses by saying the utility's study was more comprehensive and assessed overall impact on visibility, not just under the haze-producing conditions.

The SRP's study was prompted by the original park service study and a proposal in 1989 by the Environmental Protection Agency that the power plant be required to reduce sulfur dioxide emissions by 90 percent.

The EPA has estimated that it would cost $4.4 billion for the power plant to install pollution-control equipment to cut sulfur-dioxide emissions by that amount.

Sulfur dioxide can be converted to sulfate compounds, which are a main contributor to haze, particularly when there is relative high humidity, or clouds, according to Malm.

The National Research Council also has conducted a review and found that emissions from the power plant reached the canyon and that they "contributed significantly to haze" over the canyon.

The council said it could not determine specifically how much the canyon's haze should be attributed to the power plant because there are other sources of pollution in the region as well.

Morris said SRP studied only the plant's impact on Grand Canyon haze because "we have no indication there is a visibility problem any place else."

As to the wind conditions being different during the two studies, she said the SRP study indicated that January through March of 1990, the period of the SRP study, was representative of a typical winter.