The D.C. water department has begun a program to replace indoor meters with units that have an outdoor extension.

The department is seeking 100 volunteers for a 90-day test of the program. If all goes well, the department hopes to install the devices at 4,000 residences by August and to replace all indoor meters within two years.

About 25,000 of the District's 105,000 residential meters are indoors, creating problems for meter readers who frequently find no one home, according to department officials.

As a result of this limited access, readers have been estimating water use, based on past consumption, for one-third to one-half of these customers. The estimates have caused a number of disputes between customers and water officials, and have complicated efforts to establish an efficient billing system, department officials said.

The new device, which is used in Detroit and Newark, would replace the indoor meter and would be connected through a wire to a remote-controlled reading device attached to the outside of the residence. The outside device reads like an automobile odometer and provides a reading per 100 cubic feet of water used.

Participants in the test program will be asked to read the inside meter once a month, so results there can be compared with the readings on the outside meters. If the two readings are about the same, the program will be expanded, according to Enrique Jograj, water registrar for the city.

The city will pay for the $115-per-house cost for equipment and installation. All residential customers will continue to be billed every six months.

Inside meters were installed primarily in homes built in the 1920s and 1930s, Jograj said, because they could be better protected from winter. However, he said, because Washington has evolved into a town where so many people of both sexes work, water meter readers often find that no one is home to admit them.

The D.C. building code now requires water meters to be installed outside of residences.

The water department has long been a focal point of consumer complaints. Customers have complained of waiting years to be billed, of wildly inaccurate charges and of no means of redress for their problems.

Jograj, who took over as water registrar last summer, says those problems are now under control, with an expanded customer service department, six-month billings for all residential customers and readings and billing procedures that provide consistently accurate charges.