Alexandria homeowners can expect a 15 percent increase in sewer charges next year.

West End residents also may soon have a new park and library.

In a memo to the City Council, the Alexandria Sanitation Authority said the higher sewer fees will take effect Oct. 1.

It said they were brought on by increased costs of treating sewage, operating and debt service requirements and inflation.

In addition, authority members told the council Tuesday that planned increases in sewer rates over the next five years will more than double the fees that homeowners pay now.

The average Alexandria homeowner now pays about $64 a year in sewer charges; by 1990, the amount will be $139. The board pointed out that Alexandrians now pay far less than Fairfax residents, who pay $162, and Arlington homeowners, who are billed about $105.

Calling the five-year increase "outrageous," council member Robert L. Calhoun said the increase far surpassed the inflation rate. He suggested that the City Council meet with the sanitation authority board this month to discuss the increase.

Mayor James B. Moran also said the rate increase "seems to be excessive." He said that although the council cannot alter board decisions, board members would likely respond to council suggestions because the members are appointed by the council.

In a separate matter, the City Council approved the $2 million purchase of a slice of West End land to build a park, and possibly a library, for the burgeoning neighborhood.

The vacant land, a narrow 3.7-acre lot across Duke Street from Cameron Station, has been mentioned in the past by several City Council members as a prime site for the city's fourth library.

Moran, the only council member voting against the land purchase, said "I think the land is not the best place for a park."

"I fully agree we don't want any more high-rises there," he said, "but there are less costly ways to skin that cat."

The mayor said the city will lose about $28,000 annually in property tax revenues now being paid on the undeveloped lot.