Washington Suburban Sanitary Commission has unveiled plans for the construction of a water main through much of Montgomery's downcounty that will provide water to Prince George's County.

The main is necessary, officials said, because projections about population growth in Prince George's indicate that the area could see a dip in water pressure if it's not built. If pressure is not high enough, officials said, fire hoses won't operate correctly, which puts everyone in danger. Water pressure could drop 10 points below the ideal without the pipe, WSSC officials said last week before the Montgomery County Planning Board.

"We need to enhance reliable water supply to Prince George's County," said John Mitchell, project manager at WSSC, explaining that the commission's goal is to have the new main constructed before customers experience reduced water pressure.

But already residents just learning about the proposal are concerned about the pipe's impact on their quality of life. WSSC officials admit the project is a major undertaking that could result in dust and noise from construction, truck traffic as well as traffic disruptions, loss of trees and wildlife and encroachment on private property.

"It's the equivalent of somebody talking about building the Intercounty Connector in your back yard," said Jim Crowell, who lives off Tuckerman Lane in North Bethesda, at the first of three public meetings planned on the issue. Two of the proposed alignments could be located along Tuckerman Lane where Crowell lives.

Mitchell presented nine possible alignments for the underground pipe Monday at Walter Johnson High School to about 25 residents, many of whom learned about the meeting from a notice posted in their apartment complex.

All nine of the routes begin near the Montgomery County bus depot at the intersection of Tuckerman Lane and Interstate 270. The new pipe will connect to an existing main that comes from the Potomac Water Filtration Plant on the river. From there, depending on the route chosen, the pipe will run roughly 5 1/2 miles through Bethesda, Rockville, Garrett Park and Kensington before ending at Stoneybrook Road near the Mormon Temple.

There are three methods WSSC could choose to install the pipe -- each with benefits and drawbacks. The less expensive method would strip more land than the alternative, which would save more land but cost nearly four times as much.

The first involves clearing about 60 acres of trees and digging a trench to lay the pipe. After it is installed, the pipe would be covered with dirt.

The second, more expensive option, involves clearing nine acres to dig holes up to 350 feet to lower machinery into the ground so the pipe can be installed. A third option would use a combination of the two methods.

WSSC provides drinking water and sewage services to Montgomery and Prince George's counties. The pipe through Montgomery County is a necessary link in the chain of pipes that provide water to Prince George's customers.

Officials said the project will be a major one. Cost estimates range from $45 million to $175 million.

At Monday's meeting, Mitchell stressed that WSSC wants to work with the community to choose the alignment for the main. A 20- to 25-member citizens advisory committee will be formed in the next month, which will meet with WSSC officials to discuss the nine alignments and begin the process of narrowing them. To become a member, people can fill out cards at one of the public meetings, or contact the WSSC hotline at 301-206-8184.

WSSC wants the final alignment and how it will be built chosen by early next year, with construction beginning in the summer of 2007. Construction will take about three years.

Longtime Grosvenor Park resident Harriet Arshawsky said she is unhappy about the planned construction and the effect it will have on the trees and wildlife in her neighborhood.

"I wish they would just leave us alone," she said. "There's too much development. ... The county says, 'Oh, there's a tree, it must come down.'"