It was the first day of excavating a field believed to be the site of a 17th-century Moyaone Indian village in Accokeek, Md. Eighteen University of Maryland archeology students and a professor unpacked their equipment at Hard Bargain Farm several years ago with no great expectations.

But almost immediately, recalls Mitch Picciano, then one of the students, they discovered a perfect clay pipe, probably 200 years old, near the soil's surface. They went crazy with excitement. They jumped around and screamed with joy. They sat down to admire their find . . . and one of them accidently sat on the pipe and destroyed it.

Archeologists cringe when they hear that story. But what really disturbs them are stories about people who dig for artifacts in the back yards of their homes, or collectors who prowl around construction sites looking for old things that are bulldozed up -- destroying the scientific value of the item.

"On federal land, it is a federal crime; on private land, it is a scientific crime," says Mark Leone, professor of anthropology at the University of Maryland. "In America, he who owns the lands owns the artifacts. While you have the right to dig up artifacts on your property, we urge you not to. If you think you've discovered something, there are archeologists at local universities and historical societies who are willing to come and evaluate the property."

Leone, who codirects Archeological Annapolis, a 10-year study of the 18th-century social and economic history of that city, says possession of the artifact itself isn't the primary concern of archeologists. Scientific investigation is.

"When a bottle or ceramic is removed from the ground with no sicentific recording, it is taken out of its historical context and loses its scientific interpretation -- forever. Nobody will ever be able to regain that information. It is scientific and social treachery because it is meddling with the public's understanding of the past. Grass-root support and interest in archeology is best channeled not into your neighbor's back yard, but into volunteering to work at archeological sites with professionals."

Nell Sydavar spends hours every day scratching at dirt with a small trowel. In the back yard of the private residence called Shiplap -- one of the oldest homes in Annapolis (circa 1710) -- she steps over taut strings that mark 5-foot-square grids across the shell-covered lot. Gratification comes in small packages at the excavation, one of three digs this summer sponsored by Archeological Annapolis. Fingernail-sized pieces of broken pottery or a tiny wedge of glass in the scrapings are immediately bagged and labeled according to grid number, location within the square and soil layer.

"I didn't expect it to be quite so boring," says the University of Maryland junior majoring in history. An Annapolis resident, Sydavar stumbled upon Annapolis' archeological program when she read in a local newspaper about the excavation of an old wooden drainpipe. She enrolled in the university's summer field school to work alongside professional archeologists and volunteers who range from housewives to hobbyists.

"You dig up so many nails that look like hunks of rust -- but there is something exciting about it. You never know what you might find. I just never thought about all the paperwork, all the notetaking, filling out artifact bags, and labeling. But now I understand why you do it."

Shiplap is one of two private residences that have proven rich with historical data in the program's pursuit to understand 18th-century urban living -- a scientific goal that would have been impossible without the cooperation of the private owners, who let professionals do the digging.

In fact, the second site in the Maryland capital's historic district has yielded what Leone's codirector Joe Dent, another University of Maryland anthropologist, calls "a major find, a find of national significance." In the back yard of the home of the oldest printing family in American history, Leone and Dent's crew uncovered the foundation and cellar of Jonas Green's print shop where the Maryland Gazette, one of the nation's first newspapers, was published from 1740 to 1830. Workers discovered a large collection of printer's type scattered around the foundation and "out its back door" -- to date more than 7,000 pieces of type, says Leone, including an important 1 1/4-inch-square skull-and-bones piece that Green used to protest the Stamp Act.

"Some of it was garbage and some of it was lost -- stuff that fell through the cracks," says Leone, who hasn't publicly disclosed the find before now as a safeguard against "pothunters," or artifact looters. "We're finding more every day."

Archeologists agree that, like Annapolis, parts of the Washington metropolitan area offer spectacular possibilities for archeological study. Unlike New York and Boston, where industrialization and development plowed under much archeological record, locations such as Georgetown, Old Town Alexandria and some neighborhoods on the outskirts of the District experienced little development.

"When you walk across 17th and Constitution . . . somewhere 15 to 20 feet below you are the artifacts of a prehistoric village," says Steven Potter, archeologist with the National Park Service's National Capital Region, who calls Washington and its environs a wealth of prehistoric and historic archeology. "The Rock Creek Valley was, in effect, a prehistoric industrial center. It is lined with prehistoric quarry sites dating back to 2000 B.C."

On Friday, Potter had to rush over to the Georgetown waterfront property at 31st and K streets NW. Contractors bulldozing the strip uncovered, he says, "what look like 18th-century warehouses with original stone floors . . . a major archeological find." Potter can't hide his enthusiasm when talking of other nearby sites: Maryland Heights, a Civil War campgrounds and bastion on the Maryland side of Harpers Ferry, where archeological excavation will start this fall. But the avoidable destruction of archeological record concerns him.

"I'm in charge of 88,000 square acres of public land and I can't stop all pothunters and relic collectors," he says. "You can imagine how difficult it is to address the problem of private homeowners digging up artifacts in their yards. "

Peter M. Kranz, a Washington paleontologist, blames part of the problem on the District government. While looking for dinosaur bones -- not uncommon in this area, Kranz says -- at a construction site at 19th and M streets a few years ago, he discovered pieces of old leather and pottery. "I gathered the items away from the construction work and tried to find a city archeologist," he says. "I couldn't find one, so I called the historical society." He finally contacted an archeologist in Alexandria.

"We determined the artifacts were pre-Civil War but probably dumped there afterward," says Kranz, whose frustration led him to establish Archeology for Amateurs. "I decided Washington didn't have an archeology program for the public, so I started one."

The city of Alexandria has blazed the path in urban archeology in America, starting in the mid-'60s. "We know that people get excited about what they read and want to dig down in their back yards or wells," says Steven Shephard, archeologist with Alexandria Archeology, a public-funded city institution that attempts to boost public participation in archeology. "We've always encouraged people to contact us when they find something -- just let us take a look at it, record any details about it and map out any find. It's not just a question of uncovering an old bottle, it's a question of uncovering information about Alexandria as a whole."

Shephard says his office receives more calls than it can quickly respond to about wells, old privies and foundations that have been found. "In one case, a contractor uncovered an old well and contacted us at the end of the day. By the next morning when we got there, it was totally dug out by an untrained person.

"What's really sad is to see the dirt piled up, with pieces of leather goods, glass and bone -- all that can tell us about the people who owned those things and what their lives were like. But in that pile it means nothing. An isolated artifact might be nice to display in your study, but if it's lost from its context, the loss of knowledge is just too tremendous."