Developers who hope to build Charles County's first trailer park proposed under a new mobile home zone are planning a presentation which is designed to convince doubters that the development would be an affordable, yet tasteful, addition to the neighborhood when the volatile issue comes before local planning commissioners here Monday.

Some residents oppose changing the existing R-2 zoning of the 350-acre parcel in Ripley, to that of a new mobile home park zone created last July because they fear declining property values and "undesirable elements" would quickly follow.

Another major concern is how to supply the mobile homes with sewer and water in an area where no hookups to existing facilities are planned by the county.

"The area is renowned for septic and water problems. We are afraid we will lose our well water if they are allowed to tap into the same deep acquifer," or underground river, said Joan F. Crownover of Ripley.

Local entrepreneur William F. Chaney and his three sons want to put a maximum of 350 trailer homes on 50 of the site's 350 acres, west of La Plata off Rte 225. The parcel abuts the 831-acre state-managed Myrtle Grove hunting and wildlife area, and state officials want the zoning changed denied because of safety concerns.

"We are not against mobile home developments per se, it is just our feeling that residents of this park are bound to treat the adjacent land as an extension of their own backyards and wander in," said Jim Mallow, assistant director of Maryland Forest, Park and Wildlife Service. Mallow said as many as 60 sportsmen hunt ducks, deer, quail and rabbits or practice on the shooting range at any one time.

If the planning commission recommends approving the new zoning, the proposal will then go to a public hearing before the Charles County Commissioners, who have the final say.

"We know we will have to do a Madison Avenue-type sales job, and we plan to," said Charles D. Ellison, an engineering consultant with D. H. Steffens Co., the firm handling Monday's presentation.

There are seven trailer parks in Charles County, none of which comply with new, tougher zoning requirements. Under a grandfather clause, the older parks may continue to exist, provided they comply with the much stricter density and aesthetic codes over the next several years, local planners said.

In 1961, Charles County outlawed free-standing trailer homes, but because of the difficulty of enforcing such a ban and the shortage of moderate-priced homes in this rural area, the prohibition went largely unheeded. After two attempts, in 1972 and 1978, to register the illegal trailers, local officials now estimate there are at least 800 on private lots. About 2 percent of the county's 72,000 residents live in mobile homes.

The creation of a mobile home zone last July was designed to cluster all such communities in areas where they could be more closely monitored for health and housing code violations, said county planner John Mudd. In the future, single trailers will be legal only on 25-acre parcels, or if they are approved replacement homes to ones occupied by the same owners.

Ellison is quick to admit that the older breed of trailer homes deserve the bad image they have with many people. "The older homes predate any standards. Most people would be right to consider them unattractive and unappealing," he said.

The new generation of mobile home comes in double width, one- and two-story models with cathedral or beamed ceilings, natural wood exteriors, shingled roofs, jacuzzi pools and dishwashers as options. Prices range from $15,000 to $30,000, with monthly rents starting at $350 said Ellison, whose engineering firm has designed similar parks in St. Mary's County, where zoning for this type of housing is more lenient than in many areas of the state.

William Chaney said citizens' fears that his development will be a blight on the rural scene are unfounded. "This mobile park will be on a 50-acre plot in the middle of a larger 350-acre site. It will be surrounded by woods. And will be at least 400 feet from the road to the first trailer," Chaney said.

However, the same doubts exist in Charles County as those voiced last fall when Prince George's County residents out-shouted developers who wanted to locate that jurisdiction's 10th mobile home park in Accokeek, just north of the Charles County line.

Ripley resident Carmen T. Stinnett said she'll be at Monday's meeting because "the park will bring complications . . . . More people, more noise, more trouble. All the kids will go ripping through the woods on their motorbikes."

Cecil and Effa Burdette, both retired, said the mobile home community is the "last thing Ripley needs."

"This is a quiet, safe, nice neighborhood. Everyone owns their home here. We're afraid it would attract the wrong kind of people and degrade our community. They wouldn't respect our property," Effa Burdette said.

Ellison said such reasoning ignores the fact that "real estate markets have made houses in a traditional sense less and less affordable to more and more people."

Town houses in the St. Charles area of Waldorf run $50,000 to $60,000 now, with the average detached single-family home running close to $80,000, Ellison said. "The change in housing values means that the type of people living in Ripley now are the very same who will be looking at these mobile homes," Ellison said.

He also called the wilderness issue raised by the state wildlife service a "false one. We would not have any problem with posting the area. People can live there now because it is already zoned residential. The same logic would apply to the nearby Board of Education site. They could always say, 'Don't build a school there because of the hunters.' "

Joan Crownover said her concern is less an emotional one than a question of already strained water resources in the Ripley area. She said the swampy land, served entirely by wells and septic systems, will not support the proposed seven trailers per acre.

"Right now, we are only allowed one house per three to five acres," she said.

Ellison agreed that the water question is the most legitimate of all the concerns, and the one his engineering group has spent the most time researching.

Under county law, the cost of all water hookups or alternative sewage-treatment systems must be borne by the developer. One option, to run a connector to the Mattawoman interceptor, is unlikely, but not impossible, because of expense, said Loretta Williams of the public works department.

Ellison said on-site sewage disposal using drying and spraying techniques or mounds are also being explored. "I think we've got a viable on-site solution that will meet the code," he said.

The question of mobile home develpment is especially important in a county like Charles where county commissioners voted to stop building federally subsidized housing in 1983. Many mobile home owners and developers say their type of housing helps fill a low-cost housing vacuum, especially for the elderly and others on fixed incomes.

Ellison said that the negative image of trailer homes ignores the new zones created in both Charles and St. Mary's counties. "These zones set development standards, require landscaping, tot lots and play areas, and insist that anyone coming into an area do a certain amount of work to maintain a tasteful, clean environment."