It was not a ride through scenic foothills or an athletic competition, but a history lesson instead--15 miles of Alexandria's little-known archaeological gems seen from a bicycle.

Thirty-one riders and history buffs from the Washington area took to their wheels for four hours yesterday, inaugurating what city officials are calling the nation's first urban archaeological trail.

The Alexandria Heritage Trail, a 22-mile loop from the Potomac River to the city's west end, winds by a prehistoric Native American preserve, a World War I-era shipyard, a Civil War fort, one of the first free black neighborhoods and 55 other sites before joining the Mount Vernon Trail.

"You're biking through 8,000 years of human history," said Pam Cressey, Alexandria's full-time archaeologist for the last 22 years. The trail, inaugurated by local officials in a ceremony yesterday as part of a weekend festival celebrating the city's archaeological past, runs along city streets and involved no new construction. But the route never had been mapped out before as a historic loop.

City officials and bike groups eager to generate interest in Alexandria as a cycling destination decided to designate the trail as part of the city's year-long 250th anniversary celebration. Organizers hope eventually to mark the sites with uniform signs that describe their history.

City officials also plan to petition the U.S. Department of the Interior to designate the trail the Alexandria loop of the Potomac Heritage National Scenic Trail, which now winds through Northern Virginia.

"We'd like to be the first local government to join the nationally designated trail," Cressey said.

Although most visitors to Alexandria gravitate to Old Town, much of the city's rich past can be found in its newer, more suburban neighborhoods, archaeologists said. Only a quarter of the new heritage trail passes through Old Town.

"We're trying to make people aware there's a lot more heritage to Alexandria than Old Town," said Chan Mohney, an archaeologist leading yesterday's tour.

The trail also promotes some of the city's more populist heritage, winding by the homes of rock stars Jim Morrison of the Doors and Cass Elliot of the Mamas and the Papas, both Alexandria natives. Former homes of Civil War Gen. Robert E. Lee and presidents Gerald Ford, Richard Nixon and George Washington--not Mount Vernon but a town house Washington lived in at 508 Cameron St.--also are featured.

The trail's other highlights include the second-oldest known black cemetery, Silver Leaf Society Cemetery, where the graves of 26 people are preserved; and the Stonegate Archaeological Preserve, where Native Americans made stone tools.

There are several little-known churches, including the Protestant Episcopal Theological Seminary, used as a hospital during the Civil War, and Oakland Baptist Church, established more than 100 years ago under an arbor by African Americans living in the village at Fort Ward.

With cue sheets in hand, the bike riders set off from Jones Point underneath the Woodrow Wilson Bridge, headed through Old Town and continued west along Eisenhower Avenue above the Capital Beltway and across Interstate 395 to Braddock Road.

They stopped for lunch at Shuter's Hill, a former plantation and Civil War fort overlooking Old Town that's an ongoing excavation site.

The riders said they were delighted to stumble on history they otherwise might have missed.

"You could go right by something and not know it's there," said Bill Higgins, 75, who lives in the Alexandria section of Fairfax County and is an avid bicyclist.

CAPTION: The Wilkes Street tunnel, which allowed Orange and Alexandria Railroad trains to access ports on the Potomac, is part of the new Alexandria Heritage Trail.