Suburban Maryland residents may be able to avoid the expenditure of up to $100 million in coming years if they are willing to go without watering their lawns during severe droughts that may occur only every 25, 50 or 100 years. Montgomery Council President John Menke told a House District Subcommittee yesterday.

Menke gave an analysis of future water needs before the Regional Affairs Subcommittee, whose chairman, Rep. Herbert E. Harris II (D-Va.) praised Maryland officials for taking steps to assure a steady water supply without wasting it.

"You folks are just ahead" of Northern Virginia, said Harris, who last week accused officials in suburban Virginia of failing to take all available actions to avert a water shortage there last summer.

Menke, who with Prince George's Councilman William Amonett is co-chairman of a bicounty Water Supply Task Force, said their study of available water and projected, needs indicate that the need for water storage previously had been over-estimated by about 100 percent.

"Far less expensive and disruptive facilities could be considered" in planning future water projects, Menke said.

Menke said residents of the two counties should be asked: "Is it worth spending an extra $100 million on drought projects simply to be able to allow lawn watering in the midst of the worst drought in 100 years?"

Hiw own answer, he said, is "nuts to that."

The task force tentatively has decided to recommend three major projects later this year.

One outlines a five-stage conservation policy during droughts, ranging from caution during business hours to a 60 percent or more cutback during extreme crises. At the third stage, for example, usage could be reduced between 15 percent and 40 percent by raising thermostat settings on air conditioners; requiring restaurants to use paper plates instead of china, and cutting off hot water faucets in public places.

Another project calls for construction of a lake on Seneca Creek in western Montgomery County that would be used in time of drought to supply water to the Potomac from which it could be pumped into the filtration plant. The reservoir, to be completed within three years, would cost about $10 million, Menke said.

The final project is a long-term development of an interconnection between the two purifying plants of the Washington Suburban Sanitary Commission (WSSC) on the Potomac and Patuxent rivers.

The interconnection, which Menke said might not be needed if other actions occur in the meantime, would be used if one plant is out of order, such as occurred after a fire last summer at the Potomac plant, or in the event of contamination of one of the rivers. That project could cost $50 million or more.

In answer to a question by Rep. Newton I. Steers (R-Md.), Menke said the reservoir is an alternative to building pipes to connect with two large existing reservoirs on the Patuxent, a project that could cost $50 million to $100 million.

Robert S. McGarry, general manager of the WSSC, said water usage in the two counties has been reduced by 3-to-4 percent in the last few years with the help of the conservation education campaign and a revised plumbing code that requires installation of water-saving devices. In November, WSSC adopted a new price structure that charges bigger users more per gallon than small users, a policy that McGarry predicted would curtail usage another couple percentage points.