By LEN MANIACE

RYE — Armed with tiny trowels and dustbins, archaeologist Bruce Byland and eight volunteers yesterday scraped away soil in search of the world inhabited by the young John Jay, years before he became a founding father to the nation.

Shortly before noon, 81-year-old volunteer Betty Young of Mamaroneck struck something hard with her trowel and called out to Byland. By itself, the flat rock Young found didn’t look like much.

But lined up with a series of other large nearby rocks, Byland said, the stones almost certainly were the foundation of a barn on the 18th century farm where the nation’s first chief justice of the Supreme Court grew up.

The week’s discovery of the foundation would begin to solve a historical mystery on the site, which is now best known for a Greek Revival mansion built in 1838 by Jay’s son Peter Augustus Jay. Although it was well documented that Jay lived there on a farm alongside Boston Post Road, all traces of the modest Jay home and several surrounding farm buildings from the earlier era vanished when the jurist’s son built his house, now known as the Jay Mansion.

At least that was true until this week, when the archaeological dig began to reveal a hidden history.

“This is the first tangible evidence of the 18th century buildings that existed when John Jay lived there,” said Anne Stillman, executive director of the Jay Heritage Center, which owns the historic buildings that remain on the site. “We’ve never seen or touched any of them before.”

Jay’s Rye home is the lesser known of two Jay sites in Westchester and is sometimes confused with the Jay Homestead in Katonah, now owned by the state, where Jay lived in retirement for 28 years until his death in 1829.

The Rye property was bought by Jay’s father, Peter Jay, in 1745, and the family moved there early the next year when John Jay was 3 months old. Jay lived there until he was 15, when he left to attend King’s College in lower Manhattan, the predecessor to Columbia University.

“The home remained an important place for Jay, and he frequently returned to it,” Stillman said. In fact, Jay is buried in a small graveyard nearby on property still owned by Jay descendants.

The Rye home and farm covered some 400 acres that today includes the Jay Heritage Center properties and the neighboring Marshlands Conservancy owned by Westchester County. The Jay family owned the property until 1906. The site was preserved in 1992 by citizen activism that blocked a development plan that originally called for demolishing the Jay Mansion and subdividing the site.

Planning for the archaeological dig began informally with discussions between Stillman and Byland, a professor at City University of New York’s Lehman College in the Bronx, who had done previous studies related to the 19th century mansion.

Armed with a drawing of the old Jay home, known as The Locusts, Byland, a Mamaroneck resident, began scouting for a depression in the land that could indicate a building once stood on the site. Eventually, the Westchester County Department of Parks was brought into the effort because the dig site turned out to be on Marshlands Conservancy land near the Jay Mansion.

Byland began the dig on Monday. A series of 13, 3-foot-by-3-foot boxes was marked off with string, and the volunteers — students, teachers and local residents — began the painstaking work of scraping away the dirt, an eighth of an inch at a time, to avoid damaging any artifacts buried there.

Along with the large foundation stones, Byland sank a series of probes in the soil that indicate a solid surface, probably the rock foundation that stretches for 40 feet, the archeologist said.

Sifting through soil removed from the site yesterday, Megan Comerford found a nonhistoric small piece of plastic — probably part of a coffee cup lid — before her look changed.

“Here’s a nail,” Comerford, a 19-year-old Providence (R.I.) College student from Hawthorne, called out.

The rusted nail contained square sides rather than rounded, exactly the type of nails used during the 18th century, Byland said.

The dig is scheduled to end today, but Byland plans to return to the site again in spring of 2004 with his students to conduct a more extensive dig. Once that study is completed, Byland hopes to obtain a funding for an extensive archeological dig.

Byland and Stillman hope this week’s discovery is just the beginning of an archaeological study that could document the entire site and eventually lead to permanent education exhibits.

“It would be nice to accurately determine where all the buildings are,” Byland said, “and to present that knowledge to the public in some engaging way.”