Sprawl is one of those puzzling public-policy phenomena that usually are best understood when seen in a rear-view mirror. People can identify sprawl once it is too late to do anything about it, but they want little to do with trying to prevent it. That costs Maine plenty in ways the state is just beginning to understand.

Evan Richert, director of the State Planning Office, has been trying to get Maine to pay attention to sprawl, which he says hurts cities by emptying them of people and businesses and hurts rural areas by introducing suburbia to a working landscape. The problem is deeply rooted in visions of the bucolic life and to often is driven by state policy.

Speaking recently at a conference on sprawl in Bar Harbor, Mark Lapping, vice president and provost at the University of Southern Maine and a dairy farmer, described the slow erosion of services that farmers depend on to keep their farms working. In place of the local vet, the tractor-repair business, the feed store are suburbanites on 10- or 15-acre tracts who are at first amazed and later incensed to learn that farming involves work and work often means noise, from tractors or chainsaws, or the double-whammy, a tractor pulling a smelly manure-spreader. The new resident fumes for awhile, then slams down his cup of cappuccino and writes an angry letter to the local selectmen.

What comes next has been repeated in all parts of Maine. The new residents want limits on noise, and, while they are at it, they want better schools and playgrounds for their children. Park development along the water would be nice and valuable, they argue, and so perhaps would a community theater. Some farmers, who are facing higher costs as services are harder to come by and farther away, wonder who will pay for the new amenities, but it isn’t easy to speak out against improved education or a prettier town. They wonder where it will all end.

Here is one place where it begins. In the latest Maine Policy Review, Mr. Richert explains that, “State government subsidizes sprawl — through its community revenue-sharing formula, transportation formulas, school construction policies, and through utility regulation that requires an averaging of costs no matter where one lives.” One startling example of sprawl comes from the Portland area, which in the 1960s was considered to be 96 square miles. Planners say the Portland area today has expanded to 626 square miles. That in part explains why Mainers are driving an additional 40 million miles a year, compared with 1980.

But the easiest place to see the cost of sprawl is in education. Maine has approximately 27,000 fewer elementary and secondary school students today than it did in 1970. Yet since 1975, state taxpayers have spent $727 million in new-school construction and additions, including $338 million to build new capacity in fast-growing towns. More new schools in suburban areas encourage further sprawl while lower enrollments in city schools means higher per-pupil costs for maintenance.

No one at the Planning Office has recommended that Maine try to stop this problem by regulating it to death. More likely, they hope enlightened self-interest — the desire to keep cities active, preserve farmland, save tax money — will drive this debate toward successful conclusions. To do that, however, means persuading the state and the public to change long-held views of land use and the subsidies that go with it.