Northern Virginia commuters wishing to join the growing number of car pools or start one of their own so they can use the HOV (high occupancy vehicle) lanes on I-66 and I-395 can now receive assistance from three regional agencies:

* The Metropolitan Washington Council of Governments (COG) operates an areawide car and van pool matching service that includes a listing of more than 10,000 persons seeking to form car pools. Telephone 783-POOL.

* In the I-66 corridor, the Northern Virginia Transportation Commission (NVTC) is now going one step further. It will update COG car pool and van pool listings. For information, telephone 524-3322.

* The private, nonprofit Virginia Vanpool Association offers counseling, plus low insurance and equipment prices for its 250 members and those wishing to start new van pools. Telephone 270-9000 weekdays from 5 to 9 p.m. for ride sharing information or 488-2577 for other information.

In addition, $1,000 interest-free loans to buy new vans are now available from NVTC.

Alexandria, Fairfax and Prince William County residents have local officials to provide special help and information about car pools and van pools. In Alexandria, call 838-4962; in Fairfax County, call 691-2323; and in Prince William County, call 369-POOL.