Archaeologists are investigating an estimated 350 sites in Northern Virginia. Although the locations generally are kept secret to protect against raids by treasure seekers and tampering by amateur archaeologists, officials say the following areas are open to the public:

* Walney Farm, Eleanore C. Lawrence Park, off Rte. 28, Centerville. The remains of Walney Farm, with sites dating back to 1850, were recently excavated by Fairfax County archaeologists. A restored home, circa 1790, near the sites has been turned into a museum.

Also at the park is a native American site dating back an estimated 8,000 years. Information and artifacts are in the museum.

* Belvoir Estate, 16th and Belvoir roads, Fort Belvoir. The ruins of a house and shop buildings on William Fairfax's 2,000-acre estate were discovered in 1973 and subsequently listed on the National Register of Historic Places. The U.S. Army Engineer Museum, near the site, has on display some of the 10,000 artifacts unearthed during excavations. Museum curators say they plan to have a comprehensive display on the archaeology of the site by early spring.

* Carlyle Wharf, 100 block of Cameron Street, Alexandria. Construction workers unearthed this 18th-century wharf earlier this month. The wharf, below Cameron Street, was once under water. City archaeologists have tentative plans to build a walk-down observation room under the street, but the exposed wharf is due to be covered soon by construction workers.

* Old King Street, 300 block, Alexandria. Archaeologists spent several years excavating this site of historic homes and shops before City Hall was built on top of it in 1977. Some artifacts discovered during excavations are on display in the city's Archaeologist Research Center, 625 King St. Workers ask those interested in examining the artifacts to call ahead at 838-4399.

* Paleo Indian Site, Gulf Branch Nature Center, 3608 Military Rd., Arlington. Museum curators say the 40 acres of park along the bluffs of the Potomac River are full of native American artifacts dating back thousands of years. A collection of artifacts is on display in the Nature Center. Visitors are allowed to dig for spearheads but are asked to report finds to center personnel so the items can be recorded.

* Sully Plantation, 328 Sully Rd., Fairfax County. The former estate of Richard Lee, across from Dulles Airport, was excavated in the mid-1970s. A restored home has been turned into a seasonal museum with artifacts on display.

* Dulin Farm, Rte. 50 and the Capital Beltway, Falls Church. The remains of a farm and military training center have been excavated and covered over at this site, which eventually will become a car dealership.