Power Plant Agrees to Stiffer Smog Curbs : Pollution: Accord calls for 90% reduction in sulfur dioxide emissions at Grand Canyon by 1999. EPA had sought a 70% cut.

The Los Angeles Department of Water and Power and other owners of a huge Arizona power plant whose emissions obscure scenic vistas at the Grand Canyon have agreed to tougher smog controls than proposed by the U.S. Environmental Protection Agency.

The agreement, to be announced today in Phoenix in Gov. Fife Symington’s office, follows months of intensive negotiations with environmentalists.

The accord calls for a 90% reduction in visibility-impairing sulfur dioxide emissions by August, 1999, at a cost of $89.6 million.

In February, the EPA--reportedly under pressure from the White House to hold down costs--said it would insist on no more than a 70% cut in emissions from the Navajo Generating Station, situated 80 miles northeast of the Grand Canyon’s South Rim.

But environmentalists, led by the Grand Canyon Trust, and operators of the 2,250-megawatt plant in Page, Ariz., said that the EPA has backed the compromise.

Owners of the plant agreed because the new controls, although stricter in the long run, will have a lower cost because of less restrictive interim compliance deadlines.

The agreement was hailed Wednesday as a forerunner of future efforts to protect the pristine air of the nation’s national parks and wilderness areas, many of which are under a growing smog siege.

If the controls are accepted by the EPA, as expected, it will mark the first time since Congress enacted the Clean Air Act in 1977 that the law has been invoked to specifically protect air quality in national parks and wilderness areas.

“I do not think that it abuses the word to call this agreement truly historic,” said Ed Norton, president of the Grand Canyon Trust, which was one of the principal environmental negotiators of the pact.

“If the EPA adopts the . . . recommendation, it will be the first time that the agency has acted solely to protect visibility and the paramount aesthetic values of a national park,” Norton said.

Barring unforeseen developments, the EPA regulations enforcing the agreement will become final sometime after a 30-day public comment period.

Despite the agreement, operators of the plant remained at odds with environmentalists over how much cleaner the Grand Canyon’s air would be with the tougher controls.

Whatever the improvement, both sides agreed that it would be substantial. One study said that 40% of the man-made haze over the park could be blamed on the plant, which is said to be the largest source of sulfur dioxide emissions in the Southwest.

Under terms of the agreement, owners of the plant will be given until August, 1999, to complete the installation of pollution controls--two months earlier than the EPA proposed last February.

However, plant owners will be given two additional years to start fitting the controls on the power plant. Moreover, by averaging pollution on a yearly basis instead of a monthly basis, as first proposed, operators will have more flexibility in meeting the goal. It will also save them money.

Under the old proposal, operators estimated that it would cost them $106 million to comply. Under the new approach, the costs were placed at $89.6 million.

The DWP said that the controls will cost the average homeowner, who pays $40 a month for power, another 20 cents.

The plant is operated jointly by the DWP, Salt River Project, Arizona Public Service Co., Tucson Electric Power, Nevada Power Co. and the U.S. Bureau of Reclamation.