Starting today, local telephone calls between the District, Northern Virginia and suburban Maryland will have to include the area code.

This means that dialing local calls across jurisdictional lines will require 10 digits rather than the current seven.

For example, someone calling Bethesda from the District will have to include Maryland's 301 area code first, and someone calling from Bethesda to the District will have to dial 202 first. Northern Virginia's area code is 703.

The dialing changes are being made because the Washington area is running out of phone numbers. Expansion to 10-digit dialing will create 8 million new phone numbers in the region, according to Chesapeake & Potomac Telephone Co. officials.

Calls that currently are local calls will remain so for billing purposes, however. Local calling exchanges are listed in the front of the C&P directory.

C&P advises parents to instruct their children of the changes in the dialing system, and reminds people with speed dials that they must be reprogrammed.

One particularly significant change involves Bethesda-Chevy Chase Fire and Rescue, whose ambulance services often are used by residents in Northwest Washington. District callers must use Maryland's 301 area code to reach the fire and rescue service.

Calls that are currently long-distance or regional toll calls will remain so and still will require a 1 dialed before the area code and seven-digit number. If 1 is dialed with the area code on a local call, the call will go through and will not be billed as long distance.

Local calls within the District, within Virginia or within Maryland will require only the current seven digits.