Prince William County and Leesburg area residents have long considered themselves part of the Washington scene. Starting this spring, the Chesapeake & Potomac Telephone Co. will treat them that way too.

On March 1, Northern Virginia residents who want to call a business or friend in Prince William, Manassas or Manassas Park will have to dial only seven digits, and can omit the 1-703 part of the number. Three months later, on June 29, dialing to or from Leesburg will no longer be long distance to most of Northern Virginia.

The changes will have no effect on the cost of calling between Prince William and the rest of Northern Virginia, but people calling to and from the 771, 777 and 729 exchanges in Leesburg will save more than 80 percent. Calls between the rest of Northern Virginia and both Prince William and Leesburg will be billed as "extended area" calls, which cost 1 to 3 cents a minute.

"Northern Virginia is finally going to consider us as part of their community. Isn't that great?" Prince William Board of County Supervisors Chairman Terrence Spellane (I-Coles) said yesterday.

For Prince William, eliminating the area code is the last step in a long process of uniting the county's phone system with the rest of Northern Virginia. Prince William residents stopped paying long-distance charges to call Northern Virginia two years ago.

But Arlington, Alexandria and Fairfax residents still had to dial the 1-703 because Prince William shares several exchanges with suburban Maryland, and the phone computers couldn't tell them apart, C&P official John Schear said. But when 10-digit dialing began in October, the problem was solved.

Joining Northern Virginia's calling area will add 99 cents a month to Leesburg residents' basic $12.88 local phone bills. But the cost of calling Alexandria, Arlington or most of Fairfax -- but not Prince William -- will drop more than 80 percent.

C&P's Leesburg manager Jim Ellington estimated that Leesburg residents will save money if they make more than $1.24 worth of calls to the rest of Northern Virginia a month. Conversely, the change is pure savings for Northern Virginia residents who call Leesburg, because their local rates won't go up.