Faced with the possibility of huge increases in the sewer bill it gets from the city of Alexandria, Fairfax County has stepped up efforts to have a representative on the board that runs the treatment plant used by both the county and the city.

Last week the State/Environmental Protection Agency Management Committee recommended that Alexandria and Arlington install expensive sewage treatment equipment that would neutralize the ammonia in the treated waste water going into the Potomac River. Fairfax officials said they would expect to pay most of the estimated $79 million tab, if the Alexandria Sanitation Authority decides to install the equipment.

In a letter to Alexandria officials, Fairfax County Executive J. Hamilton Lambert requested that the county be allowed a representative on the sanitation authority's board, a five-member citizens committee appointed by the City Council that sets sewage treatment rates and plant operations.

"We have a significant amount of money in the plant . It's prudent management to be involved in its fiscal management," said Richard J. Gozikowski, director of Fairfax's Office of Waste Management. Gozikowski calculated that the county would pay about $47 million toward refitting the plant for nitrification, if Alexandria decides to install the equipment.

"How did Fairfax ever get into that situation where they're paying the majority of costs with no representation?" asked Alexandria City Council member Patricia Ticer. "It seems all the equity is on the side of Fairfax representation," Ticer said.

Denton U. Kent, deputy county executive for planning and development, and Fairfax County Board of Supervisors Chairman John F. Herrity said that they didn't know how Fairfax reached the agreement with the Alexandria Sanitation Authority, which dates to the 1950s.

"It was quite a few years ago when this was arranged. It's just always been accepted," Herrity said.

"If we could, we'd like a voting member on the board ," Herrity said, "but we're not in a very strong position to make demands. The Alexandria City Council makes the appointments to the sanitation authority board ."

"There's never been any controversy. They Fairfax officials have the right, like any citizen, to come before the board and make their views known," said Samuel W. Shafer, engineer-director of the Alexandria Sanitation Authority.

The Alexandria City Council deferred a decision on Fairfax's proposal until its Oct. 8 meeting.

"I'm not particularly opposed to it," said Alexandria Mayor James P. Moran.

A 1973 service agreement between Fairfax and Alexandria al"If we could, we'd like a voting member on the board , but we're not in a very strong position to make demands. The Alexandria City Council makes the appointments to the sanitation authority board. " -- John F. Herrity, Fairfax Chairman lows the county to use up to 60 percent of the South Payne Street plant's capacity of 54 million gallons per day to treat its sewage. Fairfax now uses about 56 percent of the plant, sending about 21 million gallons of sewage daily to Alexandria, and pays operating costs in proportion to its use, estimated to be about $6.6 million over the next year. The county also pays 60 percent of the capital costs for the plant, or about $1.4 million annually.

Shafer said that changing over to the nitrification would be five years away if it were done, but the city will not make a decision on EPA's recommendation until it sees the agency's reasoning. "There are many questions about the role nitrogen plays in affecting the river," Shafer said.

If nitrification is used, the cost for sewage treatment would go even higher than the 100 percent increase that is projected for Alexandrians over the next five years. The average Alexandria household pays about $64 annually for sewage treatment, but by 1990 the cost will be $139.