The recent three-day series "Investing in Sprawl" [front page, Aug. 8-10] provided a wealth of information and insight but didn't mention the elephant in the parlor: population growth.

The United States has more than 293 million people, and its population is growing at a rate far ahead of other industrialized countries. If growth continues at this rate, we will have a half-billion people by 2050. "Smart growth" alone would not be enough to offset the enormous burden such a population increase would place on the environment and the resources it provides for the functioning of the economy and the well-being of Americans.

Eighty-seven percent of this growth comes from immigrants and their children. We admit more than 1 million legal immigrants a year, and perhaps half a million more illegal immigrants come in as well (more than 10 million illegal immigrants live in the United States).

Smart growth, mass transit, and more efficient use of energy and raw materials are means toward the desired end of a good life for all Americans, but as long as the population is increasing by about 3.2 million a year, we are shooting at a moving target.

MICHAEL D. RICHARDS

Washington

The writer is policy coordinator for Population-Environment Balance.

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The front-page series on sprawl seemed to place most of the blame on restrictive land-use regulations in Montgomery, Fairfax and Loudoun counties. It also criticized these counties for trying to attract more jobs than new residents.

First, counties such as Fairfax and Montgomery do not need to build a home for every job they create because they originally developed mostly as residential communities. Now the centers of employment are moving to hubs such as Tysons Corner and the Dulles Corridor, and more people can live closer to work if they choose. The jurisdictions that already have a large base of residences do not need to create a home for every new job.

The problem is not restrictive land regulations in the inner suburbs but just the opposite -- not enough local control of land use. If local governments could set and enforce meaningful restrictions on development, residential communities would not be being built on farmland far from the job centers. Unfortunately, in Virginia, the General Assembly gives local government few powers to direct or restrict development.

Land conservation in the inner suburbs also must be addressed. The public will go along with higher density only if it is clear which areas will be preserved, and those areas need to be a reasonable distance from areas slated for higher density.

We need to plan our "green" infrastructure, setting aside the stream valleys and other lands of ecological and historical importance, and then plan the higher-density development where it does the least damage to our natural systems.

PAUL GILBERT

President

Northern Virginia Conservation Trust

Annandale

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The otherwise thorough article on commuting from West Virginia ["Washington's Road to Outward Growth," Aug. 9] omitted mention of the MARC train service used by hundreds of commuters every day. In West Virginia, the trains stop at Martinsburg, Duffields and Harpers Ferry. The next two stops, at Brunswick and Point of Rocks, are convenient to the northern part of Loudoun County.

The trains go to, among other places, Gaithersburg, Rockville, Silver Spring and Washington's Union Station.

While this service is not useful for every commuter, it is valuable for many and should have been mentioned.

TOM HOFFMAN

Pearisburg, Va.

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The series on smart growth got to the heart of the problem: Job growth in the Washington market is outpacing the availability of housing. Large-lot zoning, massive preservation zones, restrictions on mixed-use and multifamily development, and resistance to "in-fill" projects drive up the cost of housing and force many families to the region's edge.

If 10-year projections for population growth and new housing permits hold true, the region will face a shortfall of 82,000 homes, according to the series, and that's on top of an already tight housing market.

The housing crunch will worsen until elected officials, environmentalists, planners, community advocates, builders and developers work together to determine where and how this region will grow.

SUSAN MATLICK

Executive Vice President

Maryland-National Capital Building

Industry Association

Silver Spring

JIM WILLIAMS

Executive Vice President

Northern Virginia Building Industry Association

Chantilly

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Peter Whoriskey noted that Fairfax County spends $7 million a year to bring in jobs ["Space for Employers, Not for Homes," Aug. 8] and that it added 129,000 jobs to its economy during the 1990s. He noted that the number of homes in the county went up by 51,000 in the decade.

Let me add one more number: 150,000. That's how many residents Fairfax County gained in the 1990s. That's a lot of new people who deserve good public schools, libraries, parks and other services, and that's the reason Fairfax County supervisors have supported an aggressive campaign to attract business for 27 years. Residents generally take back more in public services than they contribute in taxes, while the situation is reversed for businesses. Without a thriving business economy, the two unattractive options are higher homeowner taxes or fewer services.

Fairfax County expects to have more than 1.2 million residents in 2025 -- 200,000 more than it has now. Those new residents -- an increasingly diverse group -- deserve the same services that the county has been providing for decades. County officials have shown forethought in planning and executing policies that build a diversified tax base, which helps provide a good quality of life while minimizing residents' tax burden.

GERALD L. GORDON

President and Chief Executive

Fairfax County Economic

Development Authority

Vienna