Residents of suburban Maryland are using so little water that their rates may go up.

The Washington Suburban Sanitary Commission (WSSC), the agency that provides water and sewer services for Prince George's and Montgomery counties, is scheduled to decide today whether to boost rates to offset lagging water sales.

If customers continue to abstain from using water, said Arthur P. Brigham,the WSSC spolesman, the agency's losses for the year could reach $6 million or about $5 a year for each of the 1.2 million WSSC customers.

Brigham said it's impossible to determine the amount of any increase because commissioners will try to trim expenses before setting higher rates to recover the loss from customers.

Brigham said that the drop in consumption, and ultimately the lost revenues, are due to heavy spring and summer rains that made lawn watering and other outdoor water uses unnecessary.

"this is so obviously weather-related; it doesn't have anything to do with customer conservation," he declared.

Brigham said the water-sewer agency's customers are using only about 133 million gallons of water a day, rather than the 140 million gallons that was expected. That forecast took normal conservation into account, he said, but not the "abnormal patterns" that have prevailed in recent weeks.

For WSSC commissioners, the dilemma over higher rates comes at a particularly embarrassing time.

Just last month, the agency was featured in an industry publication for the success of its conservation crusade. Written by two WSSC officials, the article described agency conservation efforts as "sincere, innovative and absolutely relentless."

No detail has escaped the agency's attention since the conservation campaign began officially in 1971. For example, it has dye tablets for customers who want to test their toilets for leaks.

In January 1978, the agency approved a special new-rate structure with 100 different prices, designed to reward the small-volume user with lower rates.

A customer using 100 gallons of water a day, for instance, would pay 25 percent less than the 200-gallon-a-day customer.

At present a household of four using 80,000 gallons of water a year pays $145.60 for WSSC services. that includes $64.80 for water and $80.80 for sewer.

The rate schedule was revised July 1 and prices for water reduced by 10 percent. Sewer prices were unchanged.

But the rains, which began in the spring, never seemed to stop, Brigham said, and all the forecasts for customer water use collapsed.

Meanwhile, waste water increased as a result of the stormy weather, he said. That added to the cost of maintaining sewer services while water revenues were declining.

"we charge according to the amount needed to operate the agency," he said. For the present year, it needed $99 million for the operating budget, he said.

But because of the reduced usage, WSSC expects to collect only $93 million, resulting in the $6 million shortfall, Brigham said.

He said he has tried to explain to customers calling his office why an increase may be needed.

"i tell them it is because of the weather - I can't say I've satisfied everybody."