WESTERNPORT - Every time the sky pours a hard rain on this remote town in Allegany County, a sickly, greenish-blue trail of raw sewage flows down the steep hill on its southern border into streets and yards.

Dogs, cats and children track the stuff into houses. The air reeks. And the waters of George's Creek, a tributary to the Potomac River that flows through town, are tainted.

The sewage comes from a collection of failing septic systems in a pocket of 32 homes on a hill just outside town limits.

"It comes right down the hill just like a squirt of tea down the side of a teacup," said Mayor Tom Smith. "It can make life very unpleasant."

Westernport is among the worst-afflicted of the hundreds of Maryland communities beset by septic failure. Many occupy rural patches of Western Maryland and the Eastern Shore, but the Baltimore area is not immune, with more than 20 communities across Carroll County and scattered homesteads in Baltimore, Anne Arundel, Harford and Howard counties subject to health risks because of failing septic systems.

Of the approximately 400,000 Maryland homes on septic, about 30,000 have failing systems, according to the Maryland Department of the Environment. Any home that has been on a septic system 25 years or longer may be at risk now or in the next decade.

Septic failures cause small- and large-scale public and environmental health problems. For communities, the effect of a rash of failures can range from noxious odors to contamination of well water.

Statewide, the combination of failures, inadequate maintenance and outdated technology enables millions of extra pounds of nitrogen to reach the Chesapeake Bay and other coastal waters every year. That makes the bay less livable for scores of species. Some state officials regard nitrogen runoff from septic systems as one of Maryland's most overlooked environmental health problems.

"For most people - if the sewage is in the ground - it's out of sight, out of mind," said Jim Dieter, program manager for the wastewater permits program at MDE.

But the problem is more complex, he said, as many working systems don't stop nitrogen from entering the water supply.

The solutions are usually clear but always expensive. Homeowners can either replace or upgrade their failing septic systems using new technology, or their communities can hook up to nearby public sewer systems. But a new septic system can cost a homeowner $10,000 or more, and monthly sewer rates can strain a tight budget as well.

In Baltimore, Howard, Anne Arundel and Harford counties, most communities that once faced widespread septic failure have connected to sewer systems during the past 20 years.

State and local officials say they lack the money or manpower to help most residents in problem areas. County health officers list target areas and help them as quickly as possible, using local funds, federal grants and a multimillion-dollar revolving loan fund run by MDE.

But their efforts are often hindered by residents who don't want the government telling them what to do with their sewage or forcing them onto costly public sewer systems.

Septic systems, which serve about 20 percent of Maryland households, have been around since the 1940s, when they began replacing outhouses in many rural areas. Most septic systems consist of a watertight underground tank that collects wastewater from the house and channels it to an underground bed of gravel, where it is trapped until bacteria and waste particles are eaten by microorganisms or absorbed into the soil. Some systems use above-ground sandpits or other variations of underground tanks.

Septic technology has improved in recent years, and some new homes feature devices that treat the wastewater before it flows to the collection tank, making it easier to absorb. Homeowners can also increase the life spans of their systems by pumping them regularly and not filling them with substances such as kitchen grease.

The waste from a septic system eventually saturates the soil around it, and that's when sewage backs up into houses and yards. Toilets won't flush, and bright patches of bog appear where sewage feeds the grass. On lots with poor soil, wastewater can seep through the ground without being absorbed and mix with water that flows into wells and streams.

A well-maintained septic system can last about 30 years. The houses in many of the state's older subdivisions have been on their septic systems for about that long. Rural towns, with tight clusters of aging houses, poor soil conditions and high ground water, tend to face the biggest septic problems.

Westernport fits that description perfectly.

The mayor's teacup description is apt, with a bed of old houses and businesses bunched between a 600-foot incline on one side and a 700-foot incline on the other. During a flood, that can mean pickup trucks floating down the creek, but during a normal shower, it means sewage everywhere.

The county wants to hook those homes to Westernport's public sewer system, but residents, many retired and living on fixed incomes, don't want to pay $40 a month in sewage fees.

Smith says he understands their resistance but he can't have his 2,400 constituents getting sick from piles of sewage, and he can't allow Westernport to dump nitrogen-contaminated refuse into a stream that feeds the Chesapeake Bay.

The problem, Smith said, is that he can't force out-of-town residents to keep their septic systems in better condition or link to the sewer system.

"I just want it cleaned up; I don't care how they do it," he said.

The county Health Department can pressure residents and has secured state money to hook the houses to public sewer lines, said Walter Finster, Allegany's director of environmental health. But that's not necessarily progress, said many residents in the trouble area.

Paul Brashear has lived on the hill outside of town for 43 years and said his septic has never caused anyone else a problem, because he maintains it properly. He can't understand why he must pay for the negligence of others.

"I'm getting ready to retire here, and all they want to do is pile more on me," he said.

The issue hasn't escaped lawmakers' attention. In 2000, a state committee recommended legislation requiring the addition of nitrogen-removal devices on all septic systems and subjecting them to regular review.

But the cost of such legislation would be catastrophic for local governments, said John E. Nickerson, a Queen Anne's County health officer who served on the committee. State legislators agreed, killing the bills in favor of spending money to improve wastewater treatment plants.

"For now, I think you still get more bang for the buck trying to improve the efficiency of treatment plants," Nickerson said.

But with so many levels of problems to fight on so many fronts, septic failure will be an issue far into the future, state and local officials said.

"I would say it has been and will continue being a high priority for us," said MDE's Dieter.