More than 150 irate Charles County residents skipped work Tuesday to voice their opposition to a mobile home park proposed for 50 acres of a 350-acre parcel near a state-managed hunting and wildlife area in the rural enclave of Ripley.

In what has become the area's most contested zoning case in the last year, lawyers representing citizens groups and owners of adjacent property paraded expert witnesses before the three county commissioners to testify that the fragile environment near the Myrtle Grove Wildlife Area would be harmed by more people, effluent and water run-off from the proposed 225-unit Hidden Pines trailer park.

"Essentially, they see a tripling of the population in what is now a very rural area," said Franklin B. Olmsted, an attorney representing two of the owners of adjacent property, Barbara and Ralph Underwood. "They see an end to their quiet little community."

The controversial Hidden Pines proposal is the first to come in under a new mobile-home zone adopted in July 1984. Two local developers and entrepreneurs, William F. Chaney and his wife Patrice, want the land changed from its current zoning category. which allows single-family homes on tracts that are at least two acres, to the mobile-home zone.

Planners say the mobile-home zone was designed to cluster trailer park developments in areas where they could be watched more closely for health and housing code violations and to offer an alternative to higher-priced houses.

Currently, there are seven trailer parks in Charles County, and planners say about 2 percent of the county's 75,000 residents live in them or in mobile homes on private lots.

The issue of mobile homes as an option to moderate- and low-income housing is especially critical in Charles, where the county commissioners voted in 1983 to stop building federally subsidized housing and where more than 1,000 families -- many of them in mobile homes -- still are without indoor toilets, running water or safe, efficient heating systems.

"This development would meet the demand for affordable housing below the $72,000 median price of a home in the county," said Charles D. Ellison, an engineering consultant handling the developer's presentation before the county commissioners.

"But it would not help low-income residents," he told the commissioners. "People would need an income of between $23,400 and $32,500 to live in Hidden Pines."

In an effort to quell critics' fears that "transients" and "undesirables" would make the park their home, Ellison told the packed auditorium that the trailer park would not attract the "riff-raff you are worried about from adjacent counties." Prices for the units will range from $15,000 to $45,000.

Central to the whole development issue is the timing and feasibility of water and sewer service. The new trailer ordinance requires that any proposed trailer park be served by public facilities, which are not scheduled for the Ripley area until the mid-1990s at the earliest, according to a technical report prepared by county planners.

Ellison said Chaney will ask the county to advance the trailer park on the waiting list, so that the development will be eligible for sewer service sooner.

The Chaneys also have agreed to give 155 acres that separate the proposed mobile park from the Mrytle Grove shooting range and wildlife area to the state in exchange for a sewer easement. Ellison said the buffer zone created by this land would keep children from wandering onto the shooting range and negate many of the environmental concerns raised.

County health officials say the Ripley area long has been plagued by failing septic systems and contaminated wells.

David John Preece, a soils and environmental consultant, testified that the development leaves a host of unanswered environmental questions.

State officials with the Maryland Forest, Park and Wildlife Service want the zoning request denied because of environmental and safety concerns.

The public hearing before Charles' three county commissioners was the last in a series of prolonged and often rancorous public meetings since January 1985 when the proposal first was presented. After more than 40 hours of testimony last summer, the county's planning commission remained deadlocked on whether to approve Chaney's plans, and sent the proposal on to the county commissioners without a recommendation.

The commissioners are scheduled to decide the case in March.