Prince William developers would be required to protect new homeowners from noise along busy streets, plant varying tree species, add more parking and build curbs instead of open drainage ditches under new guidelines to be proposed by county planners.

The changes, if approved by the Board of County Supervisors early next year, would be mandated by the county's Design and Construction Standards manual, a set of guidelines for developers of residential and commercial projects.

The changes have been under discussion between county planners and local builders for about a year. They reflect an effort to respond to residents' concerns about what they hear and see in their new subdivisions.

Some of the guidelines will give new developments a more suburban feel. Others attempt to restore a more natural environment, said Nimet El-Alaily, the county's deputy planning director.

The new standards would affect residential projects most significantly, and many developers claim they would drive up their costs. The proposed guidelines include:

* Parking. Town houses and other multi-family projects would increase parking spaces set aside for each unit to 2.7, from 2.5, adding about 20 spaces to a 100-unit development.

* Noise abatement. If a developer builds near a major roadway, any homes within 100 feet of the road would be separated from it by berms or dirt mounds to buffer the street noise.

* Landscaping. Developers would be asked to replace common trees such as white pines with native species that grew on the property before it was razed for development. "We're trying to tell developers, 'If you're not going to preserve the trees, replace them,' " El-Alaily said.

* Curbs and gutters. Commercial and residential projects in the county's eastern end on lots one acre or smaller would be required to install curbs, gutters and storm sewers instead of the ditch drainage system now used in many areas.

The county will hold public hearings on the standards early next year.

"We're becoming less rural and more suburban," El-Alaily said of the curb measure, which would not affect the county's western end since it has fewer sewer systems. "It will definitely look different. People often look at the ditches on the side of the road and say, "When is the road going to be finished?"

The proposal has brought mixed reviews from developers, depending on how complicated and costly the proposed changes would be. The noise abatement policy, for example, would require builders to erect expensive sound walls or relocate homes away from busy roads--a move they predict would increase, rather than limit, sprawl.

"If you move the house, you reduce the density of the property and encourage the sprawl," said Michael Anderson, outgoing president of the Prince William chapter of the Northern Virginia Building Industry Association. He said sound walls could add "hundreds of thousands of dollars" to the cost of new houses.

Anderson also disputed county planners' claims that Prince William residents are seeking a more suburban rather than rural environment in their new developments. Open ditches for drainage, he said, "communicate a kind of rural look" with more winding and hilly roads.