Thousands of Montgomery County residents ushered in the new year yesterday without showers or drinking water, due to a break in a major water line that left the Gaithersburg-Olney area dry until early afternoon.

Officials of the Washington Suburban Sanitary Commission discovered the break in a 48-inch trunk line near Lake Needwood north of Rockville shortly after midnight Friday, according to Al Richardson of the WSSC's maintenance section. Richardson said that the pipe supplied water to much of the northern half of the county and that the rupture caused water pressure across that area to plummet.

Initially, officials said, the break knocked out service to almost half of the county's 665,000 residents. But by 4:30 a.m. repairs on the line had begun and water was restored to all but about 75,000 people north of Rockville from I-270 east to Georgia Avenue.

That area, however, was dry until about 1 p.m. Officials said that the delay there was due in part to high demand in adjacent communities, which made it impossible to raise water pressure in the hardest-hit areas.

Richardson said that all residents affected by the break probably saw some discoloration of their water throughout Friday, but said that it remained safe to drink. He said that the discolored water might stain clothes if used in washing, but said that the water should be clear again by today.

WSSC officials logged hundreds of telephone calls in the early hours yesterday and eventually used a taped message telling customers that "a major transmission break" had temporarily disrupted their service.

A Montgomery County fire dispatcher said that after the line break was discovered the department stationed water tank trucks across the northern part of the county to supplement its supply. But he said that no major fires occurred while the lines were dry.