Montgomery County officials last week granted "pre-preliminary" approval for plants to develop a 157-acre tract of land known as Snowdens Mill that will have, if the final construction okay is given, a controversial sewage treatment plant.

The plant would use the land treatment process, a method favored by environmentalists and citizen's groups in the area.

Civic associations, however, turned out in force at the county planning commission meeting last Thursday to oppose the Snowden Hill proposal, saying the sewage facility as it is now planned would be costly, too close to residential areas and a danger to the health of residents of the northeastern Montgomery County area. The Snowdens Mill property is located on the north side of Randolph Road between Old Columbia Pike and the Paint Branch Stream Valley Park.

Approval or disapproval of the sewage treatment facilities will not be considered until the developer, Tera-Deka, Inc., returns to the commission with detailed plans for construction, sewage handling and other facilities. The planning group only gave permission to Tera-Deka to go ahead with "cluster development" plans for building town houses and single-family dwellings in varying designs on varied sizes of lots.

Several sewer moratoria in Montgomery County have slowed housing construction in recent years and have led builders to seek permission to build their own treatment plants so that they can go on with development.

After plants are built with private funds, they are turned over to the Washington Suburban and Sanitary Commission for operation and maintenance at public expense. The "ultimate plan" for the Snowden Mill plant calls for it to be dismantled when public sewer facilities become available, said John J. Broda, head of the county's development review division.

Although approval of sewerage facilities was not at issue last week, the citizens groups concentrated their attacks on the proposed plant. In the land treatment process, sewage is cleansed of polutants and sprayed on the land. Ideally, it is used to irrigate crops or woodland. In the case of Snowdens Mill the effluent will simply be sprayed on a field reserved only to absorb it.

The "cluster plant is so intimately tied to environmental factors" associated with the proposed sewerage plant that the two must be considered together, Sheridan Neimark, an attorney and a spokesman for the Stonecrest-Woodcrest Civic Association told the planning commission. Neimark said his organization believes that the "spray field, the buffer zone and the holding pond" are too small to insure that there will be no health hazard.

In a letter submitted to the commission, five organizations representing residents in developments around Snowdens Mill said that "recent scientific literature and experience" indicate that placing a land treatment plant in a populated area could spread "potentially serious illnesses."

The developer counters that tests show that the purification processes to be used at Snowdens Mill are so effective that the effluent will not carry disease, and will be almost drinkable.

The cost of operating the Snowdens Mill plant will be seven times the amount the WSSC pays on the average of treat sewage, said Michael Gravitz of the Clean Water Action Project. The high cost will be due to the extensive treatement of the water planned at Snowdens Mill and the relatively small amount of sewage - 82,000 gallons per day - to be processed, he said, adding that "the exorbitant cost of treating sewage at Snowdens Mill will be borne by all WSSC rate payers."

In most land treatment plants, Gravitz said later, the sewage is treated enough to remove polutants but not the nutrients and then is used for irrigation. At Snowdens Mill, the sewage is to be treated more extensively, apparently to alleviate fears of residents in the area.

The County Council already has approved construction of a land treatment plant at the Snowdens Mill site, but the developers must obtain approval from the planning commission for their specific plans. One other land treatment plant has been built in Montgomery County - at the Rossmoor development - and will be ready to begin operations within a few weeks, said a county official.