Old Lyme, Conn. — Behind a family vegetable garden in this historic seaside town, in a big rectangular pit that occupies most of the remaining yard, area students and interested adults have been laboring - and learning - all summer long. They've been excavating a site where people lived some 4,500 years ago.
Supervising the dig is John (Ned) Pfeiffer, an Old Lyme resident who is working on his doctorate in archaeology at the State University of New York, Albany, and who has firm ideas about how youngsters can learn and contribute.
To understand something, he noted, ''A student must see it, touch it, know it's real.''
Young people who have worked at the site (beside volunteers from the Archaeological Society of Southeastern Connecticut) range from fourth-graders to graduate students. They've seen ''post molds'' (dark marks in the soil where it's thought that stakes supported a wigwam) and held ancient tools made of quartzite, flint, and slate.
''Everyone here has made discoveries,'' Mr. Pfeiffer said. ''Right, Nan?''
Ninth-grader Nan Barnes responded, ''Well, I found just a couple of points [ projectiles].''
''Justm a couple of points!'' exclaimed Mr. Pfeiffer, smiling. He noted, ''Even at a young age, you can make a legitimate contribution to science.''
The group's discoveries have included hearths, a variety of artifacts, the post molds (from what may prove to be one of the earliest ''houses'' ever found in New England), and a cluster of stone tools and chips indicating a ''workshop'' was there.
Mr. Pfeiffer has also excavated two nearby cremation burial sites. Those digs and this summer's, according to Robert E. Funk, state archaeologist for New York , who has visited the three sites, ''shed light on the archaeology of the whole Northeast.''
Dr. Funk noted that Mr. Pfeiffer and his helpers link their finds to Laurentian settlements found only in northern New England and New York State. ''He's made some important discoveries,'' Funk said, adding praise for ''those volunteers working day after day.''
Not that that's been easy. ''When I got home from here the first two days,'' said Fiona Leek, one of two students at the site from Wesleyan University, Middletown, Conn., ''I was flat out.''
The pit (carefully divided into one-meter squares) has grown to be 14 meters long, 8 meters wide, and a meter deep. The mound of earth removed from it, noted Pfeiffer, ''equals about 25 truckloads.'' The workers lug buckets of earth from the pit to the top of the mound, there carefully shaking the contents through screens in search of artifacts.
''The little kids,'' said Miss Leek admiringly, ''hauled buckets that must have weighed almost as much as they do.''
The 10 youngest diggers were participants in a summer program run by Project Learn, based in next-door East Lyme, which provides various educational services in the region.
Their teacher, Geraldine Golet (a former elementary school principal and an enthusiastic amateur archaeologist), has worked with youngsters at several sites over the past three summers.
The five high school students at the site will receive academic credit for their efforts through Lyme-Old Lyme High School. ''It's a heck of a commitment on their part,'' said Bruce Chandler, Old Lyme's summer school director, noting their all-day participation through hot, humid ''beach weather.''
Mr. Chandler said, ''John [Pfeiffer] doesn't just give the kids shovels and say, 'Go to work.' He's always teaching. His love of what he does comes through. We hope we can offer the course again next year.''
Tenth-grader Bill Brown explained why he signed up for the course. ''I always wondered how the Indians lived - how they managedm.''
Nan Barnes described what kept her at work in the pit. ''Each day you trowel, shovel, and bucket,'' she said, ''and pray you'll find something.'' She added, ''Usually the kid next to you does.''
A nearby adult volunteer, Sarah Langley, chuckled. ''That is how you get hooked,'' said Dr. Langley, who is associate professor of anthropology at Eastern Connecticut State University in Willimantic, and leader herself of a dig near Branford, farther west on the Connecticut coastline.
The students have learned proper techniques for trowel and shovel work. ''You must keep the area flat when you're troweling,'' explained Miss Leek, ''and take off a whole layer at one time. If you do it right, you can sometimes turn up artifacts when they're actually in place, not just in the screen.''
They've also learned that items found must not be separated from the whole scene. ''We're looking for patterns of human behavior, not things,'' Dr. Langley repeated. Students showed visitors their finds in plastic bags, properly labeled (where found, which square, how deep) to be part of the site collection.
The students have come to appreciate concern for what remains of early cultures. Eyeing Jean Bliss, who with her husband, Philip, gave Pfeiffer permission to turn their once grassy and pleasant yard into a dusty pit (and who trowels daily in it), an eighth-grader observed, ''She's a very nice person. She knows how important this is.''
Another student cited her mother's idea that she might apply her new skills elsewhere. ''My room at home's really a mess,'' she said, ''so my mom's going to mark it off in one-meter squares.''