Five companies have expressed interest in buying the giant water and sewer agency serving Washington's Maryland suburbs as officials open a series of public discussions on whether the agency should be put on the market.

The first hearing on whether the Washington Suburban Sanitary Commission should be sold--either entirely or by select operations and assets--is scheduled for tonight. But companies already are trying to influence what could be a $3 billion sale.

At least one company interested in bidding on the WSSC has started lobbying residents of Montgomery and Prince George's counties to support the sale, a move that would make it a regulated utility similar to power companies. The letter-writing campaign is being conducted by Hanifin Associates, a Laurel consulting firm whose clients include New Jersey-based American Water System.

If sold, the agency now run by the two counties would become the nation's largest privately owned water and sewer company with annual revenues of more than $650 million. Supporters of the sale say it would generate a financial windfall for the counties running an agency saddled with $1 billion in bond debt. A private owner could pay down the WSSC's debt, and having less interest to pay could lead to lower rates for the WSSC's 1.6 million customers.

A study by the WSSC's privatization task force estimates that the down payment alone could bring Montgomery and Prince George's $1 billion. It also predicts that lifting the WSSC's tax exemption would generate $20 million in annual property tax revenue for each county.

But opponents fear private ownership would make the utility less accountable to the public, particularly since several businesses interested in buying all or parts of the WSSC are based in Europe.

"There are a lot of different views and a lot of interested parties," said Kevin P. Maloney, a WSSC commissioner and co-chairman of the privatization task force. "There are some people who just fear change and some people who fear the loss of control."

The public hearing, scheduled for 6:30 tonight at Eleanor Roosevelt High School in Greenbelt, will be the first since the Maryland General Assembly ordered the agency to study privatization last year. The 15-member task force must submit its report by Sept. 1 to the General Assembly, which will make the ultimate decision on the agency's future.

The consultant's study does not recommend a course of action. Instead, it outlines four options including a complete sale of agency assets, contracting out some services, or restructuring agency operations but keeping it public.

It also lists five companies potentially interested in bidding on the WSSC, three based in either France or England. That alarms some customers.

Mike Mesa, a western Montgomery resident, attended a WSSC meeting earlier this week. An audience member passed out the Hanifin Associates letter urging residents to support the WSSC's sale. Mesa had not heard of the effort until then.

"This is the most important natural resource we have," Mesa said. "To have that in control of a private organization or foreign organization is dangerous, and does not serve my needs or the needs of the community."