Alexandria's Planning and Recreation commissions have unanimously endorsed plans to drill the first of what may be a dozen water wells in the city's downtown parks.

Citizen opposition to the first well -- proposed for a small park at Union and Wilkes streets -- evaporated last week when the Virginia-American Water Company announced it could bury the most objectionable part of the well project, a 20-by-40 foot building needed to chemically treat the water.

If the City Council approves the construction of the well later this month, it could be pumping more than 500,000 gallons a day of "extremely pure well water" by next year, according to water company vice president Theodore Jones Jr.

A test well on the site found the water needed no treatment at all, but state law requires chlorination and fluoridation of all public water supplies.

The only citizen to speak at the planning commission meeting Tuesday night, C. C. Brock, said, "I raised a fuss before (over the 20-by-40-foot building), but the neighbors here are pretty confident with the new design" that would require only a 9-by-9 foot building.

The only part of the proposed wells that actually needs to be above ground, Jones says, is a small 9-by-9 foot pump house that could be surrounded by shrubbery.

Park and school sites are among the only possible locations for the wells because state law requires that public wells be located at least 50 feet from building, streets and sewer lines.

And so far only eastern Alexandria is being considered for wells because Old Town, Rosemont and Del Ray sit above a belt of sandy soil that scientists from the U.S. Geological Survey have called "among the most prolific sources of groundwater" in the Washington area.

Plans for the first downtown well -- at Wilkes and Union streets, beside Lee Street Park and the old Wilkes Street railroad tunnel -- recently were withdrawn from the Planning Commission because of opposition.

Jones estimates the saving to Alexandria customers on water brought from Fairfax County could total $191,000 per year per well, or more than $2 million annually if all 12 wells are drilled and then produce as expected. The well also would provide the city with a supply of water that is purer than river and reservoir water, and is not affected by droughts.

The other sites being considered by the water company and city officials include two at the new Four Mile Run Park and others at: the Texaco waterfront property just given the city, the Pepco power plant, George Washington High School, Founders Park, The proposed Cameron Valley Park, Lee Recreation Center, the small park at Bashford Lane by the Monroe Street (Rte. 1) bridge, and Jones Point and Daingerfield Island (both federal property).

The sites thought most likely to be requested in the near future -- besides the one at Wilkes and Union Street -- are Bashford Lane, George Washington High School, Four Mile Run and the Texaco property, according to Dayton Cook, director of the city's transportation and environmental services department.

Alexandria presently gets its water from Fairfax County's Occoquan Reservoir, built by the Virginia-American Water Co., in the 1950s but taken by condemnation by Fairfax County in 1967. Alexandria will begin using some upper Potomac River water when Fairfax opens its river intake system in 1982.

The city also has been negotiating -- so ar unsuccessfully -- to share in the area's second-oldest water system: the U.S.Army Corps of Engineers' Washington Aqueduct which supplies Potomac water at the area's lowest rates to the District and parts of Montgomery, Fairfax and Arlington counties. Pipes for such a connection would cost more than $6 million, but the water is less than half the price currently paid.

The privately owned Virginia-American Water Co., formerly the Alexandria Water Co., drilled two wells last year on its hilltop property beside the George Washngton Masonic Memorial -- where it built the Washington area's first reservoir and underground water system in 1852.

He two 380-foot wells are now each producing 500,000 gallons of water daily, or about 7 percent of the 14 million gallons the city's businesses and 120,000 residents consume every day. Jones estimates that a system of city wells could provide about one-third of Alexandria's water needs, and do it for less than the lowest rate paid for Fairfax water.

The city theoretically pays two prices for Fairfax water: 43 cents per 1,000 gallons for the first 5 billion gallons a year, and $1.38 per 1,000 gallons -- three times the basic rate -- for additional water. Because of water conservation, rainy summer weather and the two wells, Alexandria last year bought just under 5 billion gallons from Fairfax.

Alexandria residents already pay the second highest water rates in the Washington area, about $88 a year for the average family using 80,000 gallons. wThe water company in December asked the Virginia State Corporation Commission for a 15.5 percent rate increase, which would give the city the area's highest water rate, or roughly $102 a year for the average family.

When combined with the recently increased city sewer charges included on one bill -- Alexandria residents would pay close to $190 a year for the two services, approximately what Fairfax County residents pay and what suburban Maryland residents will pay within the next few months when their rates jump between 25 and 35 percent. Arlington residents pay about $127 a year. District residents pay about $90 a year, by far the lowest water-sewer rates in the area.

The proposed rate increase would provide a 9.6 percent return for the water company, a subsidiary of the American Water Works Co. which is the nation's largest investor-owned water system. Last year the company's profits were only 3.5 percent, Jones said, down from 6.2 percent in 1978 and 5.9 percent in 1977. Besides Alexandria, the water company provides water for Dulles International Airport, Dale City and Fort Belvoir.