In the 360 years since Leonard Calvert began a New World colony on the banks of the Patuxent River, the population in Central Maryland has covered more than 360,000 acres - roughly 560 square miles - with housing development.

In the next 25 years, if present trends continue, more land will be converted to housing than in the previous three and a half centuries, according to projections by the Maryland Office of Planning.

"It is more than a 100 percent increase in the area that has to have water, sewer, roads, infrastructure and schools," Ronald Kreitner, director of the planning office, told the more than 200 developers, environmentalists, and state, federal and local government officials who gathered at the recent Bay Program conference, "A Quality Landscape," to search for ways to manage growth in the region.

"You're taking on an enormous challenge," Kreitner said. He noted that the trends facing Central Maryland also apply to Virginia and Pennsylvania.

As development sprawls across the landscape, it can destroy wildlife habitat, overrun farmlands, displace valuable streamside forests, threaten wetlands, contribute to air pollution problems and increase the runoff of sediment, nutrients and toxics into local waterways and the Bay.

"Managing growth remains the single greatest challenge to the Bay's health," said Mike McCabe, administrator of EPA Region III. The difficulty has become increasingly apparent as states have developed "tributary strategies" designed to reduce nutrients in the Bay's major tributaries 40 percent by the turn of the century and then "capping" the amounts of nitrogen and phosphorus at those reduced levels.

But as roads and buildings displace undeveloped land, polluted runoff to local streams will likely increase, threatening the ability to maintain reduced nutrient levels. Acre for acre, developed land contributes more nutrients than forests, pastures or any other land use except cropland to waterways.

"The commitment to cap nutrient discharges means that growth and development cannot be ignored," McCabe said.

Steering growth away from sensitive areas and clustering it in designated areas rather than allowing it to sprawl over the countryside can reduce environmental impacts, many speakers noted. But managing land use is a job that falls into the hands of local government officials.

To more fully involve them in the Bay restoration effort, the Executive Council, at a meeting that coincided with the conference, approved a "Local Government Partnership Initiative" that outlines specific commitments to increase aid to local governments and to increase their involvement in the cleanup effort [see related story, page 7].

"Local governments are essential components to the Bay restoration effort, but a relationship must be built between us and them which is stronger, deeper, more focused and vital if that new partnership is to work effectively," said Gary Allen, chairman of the Bay Program's Local Government Advisory Committee, and mayor of Bowie, Md. "Without it, I believe that the Bay restoration goal will never be realized."

Kreitner, though, laid out a series of trends that show how daunting a task local governments and others will face in managing growth.

The picture starts with population. The number of people living in Virginia, Maryland, Pennsylvania and the District of Columbia is projected to grow from 23.5 million in 1990 to 27.5 million in 2020, with the fastest growth taking place in Virginia. But, Kreitner said, "it's very important to get beyond the population numbers, because that's really not all that we're accommodating."

For example, he said, the number of people in an average household is shrinking. In 1970, the typical household had 3.2 people. That dropped to an average of 2.67 in 1990, and the trend is expected to continue, with only 2.43 people making up a typical household in 2020.

Fewer people per household means that more houses are needed to provide homes for the same number of people. Put another way, the growth in the number of households is growing faster than the population, Kreitner said.

Development pressure comes not only from population growth and shrinking household size, but also from people abandoning already developed areas. In recent decades, Kreitner said, people have not only left the cities, but also older suburban developments near the cities.

In the past 20 years, he said, Maryland's population grew by 800,000 people, but 425,000 people moved out of urban areas. That meant there was a housing demand for 1.2 million people - 50 percent more than was needed just to handle population growth. And that rate is accelerating. While Baltimore lost 100,000 people from 1980 to 1990, another 53,000 abandoned the city between 1990 and 1994.

In addition, the amount of space used to accommodate a household has grown. In 1985, the average residential lot size in Maryland was .42 acres, Kreitner said. By 1993, that grew to .57 acres - a 36 percent increase.

"What we're facing is population growth, the growth in households, out migration from developed areas and more land per household," Kreitner said. Put together, he said, those figures indicate that a huge amount of land will be consumed to accommodate growth.

Kreitner used the trends projected for Central Maryland, which includes Baltimore and 11 counties, to illustrate the dilemma. Because of increasing lots sizes, out migration and shrinking household sizes - the projected 39.6 percent population growth for that region will consume 104 percent more land than is presently used for housing.

Actually, Kreitner said, even more land would be affected because the new developments would not be clustered together but would be scattered over the area, meaning that roads and sewer and water lines would have to be run through undeveloped land to connect them.

"It is an equal area," Kreitner said, "but scattered to the point that from a management standpoint - especially at the local level where the rubber meets the road in infrastructure management - it becomes virtually impossible to deal with for fiscal reasons as well as for many of the environmental impacts."

To manage growth, he said, "we have to use just about every avenue available. We have to look at incentives, we will have to look at education so individual decisions can be more in tune with an efficient and responsible development pattern, we have to look at changes in regulations, and in some cases that may mean deregulating areas where we want growth."

Management will be difficult, cautioned Leonard Shabman, a Virginia Tech agricultural economist, because some of the root causes of sprawl development are beyond the control of local governments. He called for "radical" changes in state and federal policies that promote sprawl.

For example, he said many local government officials believe that they need to attract high-priced commercial and residential development to increase property tax revenues. That leads them to "upzone" farmland to uses that generate more property taxes.

Shabman suggested ending local government reliance on property taxes either by giving them other revenue sources - such as income taxes - or by having states pay for schools, often the most expensive local service. Such solutions, he said, would end local government desire "to chase tax base."

Likewise, he noted low gas prices coupled with government fuel-efficiency standards have dramatically lowered the cost of commuting, thereby encouraging people to drive ever-longer distances. "To put it in perspective," he said, "the gas price would have to rise by $2 per gallon to make the cost of driving your car a mile today the same as it was less than 20 years ago."

The federal home mortgage deduction - and the deduction for second mortgages - offers additional incentives for sprawled development. He said adopting a tax system that scrapped the mortgage deduction would have "significant effects on land settlement."

Solving such problems, he suggested, would take a decade or more of consensus building among the public and private sector and other interested groups. Today, he said, there is no mechanism for such a sustained dialogue to be carried on.

From the conference, and through follow-up meetings, organizers hope to begin such a dialogue. Ultimately, they hope to develop an "action plan" that can be used to guide the Bay Program - and regional - activities to manage growth and protect resources.

Bill Matuszeski, director of the EPA's Chesapeake Bay Program Office, cautioned against expecting any quick and dramatic changes, saying that it will take time and education to affect public attitudes and perceptions that contribute to development trends.

"We need to work on the world the way it is," he said. "Current restrictions that we don't like are in many cases set by the citizens of those very communities who are there now, and who have concerns about what is coming their way."

In many ways, he said, the market is responding to the public's concern about issues such as education and crime. "These are values that we need to deal with," he said. We can't walk away from them; otherwise we're doomed."

But, Matuszeski said, an informed public that understands the links between the way development takes place and its impact on the Bay will ultimately provide a constituency for change. "I don't think things are as difficult as they might appear," he said. "We do have a tremendous amount of support. We do, of course have to broaden the participation."