With cloudy skies, a persistent drizzle and a blanket of fog that hovered over rivers, bays and streams, it was a gray Christmas here yesterday and a meteorological taste of what was expected to be a dreary weekend.

The forecast was clouds and rain today, clouds and rain tomorrow and more of the same on Monday. "It makes it pretty dismal," said National Weather Service forecaster Jeff Bowman.

Yet the fog also hinted at the mysterious and exotic at times, hugging the surface of the Potomac River so that bridge arches and abutments seemed to spring unsupported out of billowing clouds, and pedestrians and automobiles on nearby paths and roads vanished into swirls of gray.

The fog appeared to be growing denser and more widespread around the area last night, but there were no immediate indications that it was causing significant problems.

Fog in the Washington Channel was "real dense," said Sgt. Julius Little of the D.C. police harbor unit. Estimating visibility at no more than 30 feet, he warned that boaters "shouldn't be out now unless they have to be out."

Fog was "sitting on top of us" at the Chesapeake Bay Bridge toll plaza, said Officer Jeff Sharp of the Bay Bridge toll facilities police. Although the fog covered most of the bridge, he said, traffic was light and appeared to be unimpeded.

At the Woodrow Wilson Bridge, fog, "looking like smoke from a fire," was "just rolling across," reported the bridge tender. He noted no traffic problems, however.

U.S. Park Police said it appeared that fog may have contributed to minor accidents on the Baltimore-Washington Parkway and to a 15-mile-an-hour reduction from the normal speed of traffic there.

"It's real foggy here," an operations officer at Baltimore-Washington International Airport reported. He said that visibility had been reduced to less than a quarter of a mile but that the airport remained open. Better visibility was reported at National and Dulles International airports.

The fog on the Potomac, according to forecaster Bowman, represented condensation caused by contact of warm, humid air with the cool surface of the water.

Yesterday's high here was 59 degrees, Bowman said. While well below the Christmas Day record of 72 set in 1964, it was unseasonable and well above the reading for the water, which was in the low 40s.

By late yesterday, total rainfall for the day was less than 0.1 inch, but the potential existed for more than an inch today and tonight, Bowman said. Temperatures were expected to fall today, he said, and tonight could be wet, cold and miserable -- although not cold enough for snow.