Mary Bethune sees about a foot of her back yard slip into Chesapeake Bay each year. Her friends kid her about living on a precipice of peril now that her living room is just five feet away from the edge of a 70-foot cliff.

If predictions by the U.S. Geological Survey office are correct, her back yard will be all but a fond memory before long. Geologists and erosion control experts claim that one good Atlantic storm, bringing all its might up the Chesapeake, could carve another major chunk out of Bethune's yard, and with it a piece of her home.

Compared with other Chesapeake Bay homeowners who lose up to 10 feet of their valuable properties each year to erosion, Bethune doesn't have it so bad. But living with the possibility that part of her house could end up in the bay doesn't seem to bother the Randall Cliffs, Md., resident -- despite the presence nearby of houses whose former owners long ago abandoned them to the fierce erosion problem.

"I've got other things to worry about," said Bethune, who has lived in her modest house with its spectacular bay views since 1954. "If it gets so bad, I'll just take the living room off the back of the house."

Bethune is one of thousands of homeowners living on the shore of Chesapeake Bay who are reporting scary and expensive run-ins with erosion -- an increasing problem that federal, state and local officials are unable to solve with any real effectiveness.

Millions of dollars are spent each year to combat erosion and landslides in an effort to save homes and the beaches along the 7,000 miles of shoreline along the bay and its tributaries. But with an increasing number of scientists predicting a dramatic rise in sea levels throughout most of the world over the next 50 years, that money may do little more than slow erosion.

In some of the hundreds of tiny Maryland and Virginia villages that dot the coastline of the bay, workers truck tons of sand onto once-expansive beaches in an effort to halt erosion. In other areas, bulldozers push huge boulders into place along the shoreline to minimize the effects of wave action, while hopeful homeowners throughout the Chesapeake region install rock jetties in an attempt to stave off the erosion that is stealing their expensive waterfront properties.

At Point Lookout State Park in Maryland, 85 miles south of Washington, more than half of the park has disappeared to the encroaching sea during the past 100 years, according to Daryl Decesare, manager of the facility. In the past 12 years, with state officials fearing the loss of one of the state's more picturesque parks, large amounts of money have been spent to hold back the bay's waters.

At a U.S. Navy research facility in Chesapeake Beach, Md., erosion is jeopardizing a huge antenna that sits only about 50 feet from the edge of a cliff overlooking the bay. The site is eroding at a rate of two feet a year, according to Stephen Leatherman, a University of Maryland scientist who has spent the past six years studying erosion along the bay.

Four miles north of the naval station, more than $480,000 in state and local funds is being spent on a retaining wall and a massive rock embankment along the shoreline in an attempt to stop storm water from flooding the tiny waterside hamlet, as occurred last winter.

In towns throughout the Chesapeake Bay area, residents report waves where once there were beaches and docks that have been pulverized by years of tidal activity.

In Maryland alone, nearly a third of the state's 4,300 miles of bay and tributary shoreline is eroding at a rate of from one to 15 feet each year.

"There's really nothing we can do to stop erosion. It was around way before we were around," said Edward Fulford, chief of the bay's coastal division for the U.S. Army Corps of Engineers, whose office is conducting five Chesapeake Bay erosion studies. "You can protect and stabilize an area, but stabilization can also hurt other areas."

Consider, for example, the town of Long Beach, Md. In 1949, a harbor was dredged and a long rock jetty was put in place to protect the dock area. Since then, swirling currents and the protection created by the jetty have been adding sand to the beach area north of the harbor.

But the shoreline to the immediate south loses more and more of its dwindling sandy beach every year. Scientists explain that jetties can protect one area by capturing sand, but they often rob sand from another nearby portion of a coastline.

Other erosion remedies have equally damaging side-effects. Vertical bulkheads or sea walls are effective for protecting land behind the erosion structure, but only carry away sand in front of the wall because of a scouring action created by the constant movement of the water.

Like most residents living along the Bay, Albert and Dorothy Duryee of Long Beach said it helps to have a sense of humor about the erosion.

"I joke about putting big pontoons under my house," said Albert Duryee. "Every time we have a storm I say 'Put up the for-sale sign.' But then the sun comes out and I say 'Take it down.' "

But the Duryees acknowledge that the erosion they have seen in their 12 years of beachfront living can be, at the least, amazing.

"We lost 35 feet of beach overnight" following a storm two years ago, Dorothy Duryee said. In the past seven years, more than 150 feet of beach adjacent to their property has been sucked up by the bay.

Scientists and property owners say that the southern end of Long Beach loses, on average, about three feet of beach each year, particularly the unprotected beach in a nearby county park.

To combat the problem, the 20 or so Long Beach homeowners living along the town's southern coastline have installed rock jetties that stretch about 30 feet into the bay. The jetties help capture sand, as long as the wind is coming from an angle.

"Nobody likes the jetties, but it's either that or no house," said Dorothy Duryee.

Despite the erosion, house sales haven't been harmed much, according to Pat Rockhill, a Long Beach real estate agent who said prices for tiny cottages along the Bay in Long Beach often exceed $115,000.

Other Bay front homeowners said fighting erosion takes constant work and money.

"We're living on the bay with a beautiful view, but you pay for it," said George Naldjieff, a retired dentist who loses a portion of his Dares Beach, Md., back yard every time the bay's waves kick up. "You can't beat nature."

When Naldjieff moved to Dares Beach 25 years ago, his view also included about 30 feet of prime beach that was a playground for his family and other town residents. Today, waves roll where the beach was located.

Several years ago, Naldjieff, like many bayfront property owners, had the state erect a bulkhead to protect what remains of his back yard -- a protective structure that works only marginally well, he said.

The state of Maryland constructs about 30 such erosion control structures each year under a program that allows homeowners to pay for the work through a low-interest loan, according to Leonard Larese-Casanova, director of the state's erosion control program. Since the program began in 1971, more than $21 million has been financed to complete more than 400 erosion control projects for private property owners.

Erosion problems are likely to worsen in the future, according to a federal study released last week.

Water levels are expected to increase by two to three feet over the next 50 years in the Atlantic Ocean, as well as the Chesapeake Bay, according to the National Academy of Sciences. Over the next 100 years, the water levels could rise as much as six feet because of an overall warming of the earth, destruction of rain forests and air pollution from burning fossil fuels.

Such a water level rise could submerge more than half the marshes in the bay, as well as destroy more than 5,000 erosion control structures, including bulkheads and jetties, according to Leatherman of the University of Maryland and one of the authors of the academy study.

"Now much smaller storms will start causing major damage," said Leatherman, who is director of the university's coastal research lab. He said the rate of erosion along the bay will be two to five times faster than at present because of the rise in water levels.

Leatherman and other scientists said federal and state legislators should strengthen laws regulating how close structures can be built to the bay's shoreline.

"We have some planning time, but developers won't listen. They're just interested in profits," Leatherman said.

John Pomeroy, a geologist with the U.S. Geological Survey office who has been conducting a survey of landslides in Maryland, said many areas of the bay are too dangerous for new construction.

"A person can lose eight feet of property {to a landslide} overnight in some sections of the coastline," Pomeroy said. "It would be foolhardy for anyone to locate within several hundred yards of a shoreline."

But developers claim steps can be taken to reduce the dangers.

In the town of Chesapeake Beach, Kettler Bros., a Washington area development firm is building 79 upscale town houses along a 1,000-foot section of the shore. Some of the homes are less than 30 feet from the water.

But Hugh Gordon, the firm's senior vice president for residential construction, said a bulkhead planned for the spot will protect the houses.

"We would not build houses that had any serious questions or problems relating to their ability to withstand mother nature's forces," he said.

For longtime bay residents who recognize the power of the Chesapeake, erosion is nothing to consider lightly.

Dixie Moran, a Chesapeake Beach resident, has seen trees slip into the bay from the steep bank in her back yard.

At the bottom of the hill from her house, thick brush grows where a road once ran along the coastline before giving way to erosion.

"I just hope I outlive the eroding bank," Moran said.

CAPTION: Construction near water just north of Chesapeake Beach.