A top Virginia water-quality official said yesterday the state may reconsider its recent decision to relax standards for area sewage-treatment plants that discharge effluents into the Potomac River and its tributaries.

The comments by John Ariail Jr. of Arlington, the new chairman of the State Water Control Board, came after he and a number of state officials toured algae-covered sections of the upper Potomac between Woodbridge and Mount Vernon.

Flowering of the slimy blue-green aquatic plants has transformed portions of the river and some bays around Washington into something like a thick sargasso sea, the officials said.

"Disgusting," water board member David H. Miller of McLean said after the river tour.

"I think we're going to have to do something about it at our September meeting," he said.

"But what we're going to do I don't know," said Ariail.

"In a way it's a godsend," he said. The obnoxious algae, he said, has reminded area officials that the region's pollution problems cannot be considered ended because the Potomac has been relatively clean for the past decade.

The growth of algae, which last bloomed here in the 1960s and early 1970s when the Potomac was considered one of the country's most polluted rivers, typically occurs in water rich in nutrients from sewage or rainwater runoff from heavily fertilized farms and suburban lawns and gardens.

This summer's bloom apparently was triggered by a wet spring and a hot, dry summer, which state officials call "optimal environmental conditions for the growth of algae."

While the state agency can do nothing about the weather, it has the responsibility to set standards for sewage-treatment plants in Virginia. Recently, it agreed under a consent order to relax the standards it set in 1973 for discharges from treatment plants on the Potomac, standards that few of the half-dozen plants along the upper portion of the river have been able to achieve.

Noman Cole of Lorton, who headed the board during the 1970s, has charged the relaxation has allowed a plant operated by Fairfax County to discharge phosphorus nutrients that are responsible for algae blooms in the bay near his riverfront home.

Fairfax County officials angrily have denied the charge.

"I think we're probably going to have to look at the Fairfax County consent order" and those for other plants, Ariail said before going into a closed meeting in Alexandria over the algae.

He said that while there is a consensus that sewage is a factor in the algae bloom, state officials don't yet know how much of a factor it is.

Michael Grizzard, director of the Occoquan monitoring laboratory, which is doing much of the analytical work for local agencies that are studying the river, speculated yesterday that the algae bloom has been caused by a buildup of nutrients, especially phosphorus, in the river sediment from sewage discharges and runoff.

This coincides with Fairfax County's position that recent discharges from its sewage plants have not caused or greatly contributed to the present algae bloom.

Grizzard said he thought the algae was having a positive effect, bringing local officials together. "It's caused a remarkable example of cooperation," he said.