Two public agencies that have been monitoring the Potomac River said yesterday that a wet spring and unusually hot, dry summer are partially to blame for the sudden appearance of blue-green algae in area waterways.

The finding is likely to fuel a simmering debate between Fairfax County officials and the man who once led Virginia's efforts to clean up the river over the appearance of the slimy substance.

The Virginia Water Control Board and the Metropolitan Washington Council of Governments said their separate reports were prepared in response to the disagreement between Noman Cole, head of the water board during the early 1970s, and Fairfax officials who say Cole is unfairly blaming a county sewage treatment plant for the algae's appearance. Both sides contended yesterday that the reports supported their beliefs.

"We were unfairly zapped," charged Fairfax County Executive J. Hamilton Lambert. "If the plant was creating the problem, we'd take action to correct it. We don't want to be known as polluters."

Cole said the reports indicate that the county's Lower Potomac plant--along with the Northern Virginia sewage plants--are "the worst polluters of the Potomac."

Even though the reports each held the weather largely responsible for the algae, they sidestepped the main issue in the debate--the sewage plants.

"At this point it would be premature to draw any firm conclusions on the causes of this summer's unusually intense algae blooms as insufficient data is available," the Council of Governments report said. "However, it is now clear that the presence of blue-green algae. . . is widespread in the Potomac and in the 20-mile stretch from Piscataway Creek to Quantico for the first time in six years."

Cole blamed the algae cover on Virginia's recent decision to relax discharge standards for the Lower Potomac plant, upstream from his home along Pohick Bay, site of the most concentrated algae growth.

"There's something strange in there," said Thoamas Schwarberg, director of the water board's Alexandria office, supporting part of Cole's claim. "There is a sewerage plant there and you can't escape the conclusion there must be some connection between the plant and what's going on the high algae concentration. "

Lambert said the county plant is releasing a tenth of the phosphorous pollutants it did in 1970. "That river's cleaner that it's ever been," he said.

The blue-green algae, which can be toxic to fish, flourishes under certain weather conditions in waters where nutrients have collected on the water bottoms. Cole and Fairfax officials disagree over the source of those water-bottom nutrients: Cole contends the sewage plant discharge is the source; Lambert--citing yesterday's reports--said the runoff from last spring's heavy rainfall in developed areas is responsible for the nutrient buildup.

Fairfax Supervisor Audrey Moore, who frequently opposes Cole's positions, has charged that Cole is attacking the county because he is scheduled to testify against the county this fall as an expert in several lawsuits challenging a policy limiting growth in the area surrounding the county's Occoquan drinking water supply. The county contends that runoff from highly developed areas would pollute the water supply. Developers, who are opposing the county policy, say that is a bogus issue.

"He [Cole] is trying to create the image that Fairfax is a big polluter," said Moore. "If we look like big polluters, the county won't have much credibility in court in these cases."

"That has nothing to do with it," Cole said yesterday. He said he began criticizing the county and its sewage treatment plant after his children discovered thick mats of blue-green algae in the water near his home.

Almost half a dozen studies have been begun by area government agencies and private groups in an effort to determine the source of the algae, which most experts agree, probably will be killed by the onset of winter.