Anne Arundel County Executive James Lighthizer proposed new restrictions today on homebuilding along the county's waterfronts, a move he said would help fight further pollution of the Chesapeake Bay.

It would limit development in the county's most desirable residential areas -- already half built up -- where new houses generally sell for $150,000 to $250,000.

The proposed change in the county's general development plan calls for reducing the number of houses allowed per acre along the shoreline from five to two. It affects about 10,500 acres lining the bay and its tributaries in Anne Arundel.

Limiting soil runoff from construction sites and built-up property is a principal concern of the proposal, but it could also help preserve vegetation and the wetlands that filter pollution as it flows to the bay, county planners said.

Lighthizer's plan to change the county's general development plan, used as a guideline for zoning decisions, will be deliberated by the County Council this fall. The county executive said his plan reflects recommendations of the state's Critical Areas Commission, which cited shoreline development as a major cause of pollution in the Chesapeake Bay and recommended that the state severely limit and, in some places ban, construction within 1,000 feet of the bay.

Some builders and conservationists said today that while the proposed development guideline is an expected outgrowth of efforts to preserve the bay, it would have little immediate impact by itself on home building or pollution control.

"I'm sure this is going to be helpful, but let's hope this is just one building block in an overall picture," said Corby Rucker, a member of the Severn River Commission, which advises state and local governments about preservation of the broad bay tributary.

More important than the number of houses allowed per acre, he said, is the type of ground they are built upon and how problems of silt control, wetland preservation and sewage disposal are handled.

Calvin Gray, a waterfront developer and vice president of the county home builders association, said that factors other than zoning also help determine what is built.

He cited one of his current projects, for example, where he is building only 30 houses because sewer capacity is limited on land where up to 120 are allowed.

Gray said builders are "pretty much resigned" to restrictions on waterfront building.

But in the long run, said one county developer, I. Richard Priddy, severe restrictions would take away "a product . . . that people want."

Construction of fewer houses could lead to the kind of prices that would frighten off buyers who can currently afford shorefront living, he contended.

"A quarter acre or half acre is a lot more affordable than an acre or two, even to the semiaffluent or affluent," he said.

Lighthizer also said that lower densities could be justified in part by the county's lowered population projections.

In drawing up the general development plan in 1978, when the county had a population of 370,000, planners predicted that Anne Arundel would have 591,000 residents by the year 2000. They now believe the population will reach about 457,000.

Lighthizer is also seeking more intensive use of about 2,000 acres elsewhere, primarily in commercial areas, and creation of an industrial park area west of Baltimore-Washington International Airport.

County Council member Carole Baker whose Severna Park district includes the fast-growing Broadneck Peninsula near the Chesapeake Bay Bridge, said Lighthizer's proposals reflect "consciousness raising" in a county that once placed little restriction on development. While the most important reason for reducing housing density on the shore is pollution control, she said, many residents of her district are also worried that fast development is simply making the shoreline area too crowded.

"We know that if we make a mistake, it's permanent," she said.