Water was restored yesterday to thousands of Northern Virginia residents in Falls Church and McLean who since Friday night had been left high and dry.

A break in the area's primary water main was blamed on antiquated pines in Falls Church, whose pumping stations also serve portions of Fairfax County. Earlier this year, metal fatigue cased a similar break in the same main, leaving customers withut water for several days and requiring city officials to call in an outside contractor with special equipment to fix it.

After the break Friday, work crews stayed on the job through the night trying to restore service through the 24-inch pipe. "You've got to give 'em credit," said a spokesman for the city's water authority. "That pipe pushes a whole lot of water."

Telephones at the main pumping station were ringing off the hook as late as yesterday afternoon, even through the break had been repaired around 9 a.m. Authorities explained that it took several hours after the pumps had been turned back on for the city's tanks to fill again and the system to build up pressure.

High areas were the worst off. Residents in the Seven Corners area, for instance, still had trouble drawing tap water well into the afternoon.