Snow squalls, sharp winds and plunging temperatures hit the Washington area yesterday, suddenly reversing the weekend's spring-like balminess. The rest of the nation also reeled under freakish weather conditions, ranging from tornadoes in Florida to shore-eroding high tides in California.

Fast falling snow - part of a massive cold front extending from Florida to New England - struck here early, snarling morning commuter traffic and causing hundreds of minor accidents.

Winds gusting to 50 miles per hour felled trees, toppled the top three stories of an office building under construction in Fairfax City and crushed a car under a fallen tree in Gaithersburg. No injuries were reported.

The snow stopped abruptly before noon, but ice formed on many roads and remained throughout the day as temperatures fell below the freezing mark and headed for the coldest weather so far this season last night.

Thought the snow stopped, the National Weather Service predicted continued cold weather at least through Thursday. Skies generally should be fair for the next day or two, but some rain or snow may return on Friday with the expected moderation in temperatures.

Road crews in the city and suburbs spread rock salt and sand on most major arterials yesterday and officials generally reported fewer tie-ups and accidents during the evening rush hour than in the morning.

The most serious accident involved a 19-car chain reaction smashup on Interstate 95 near Laurel in Howard Country yesterday morning. Maryland state police reported a southbound tractor trailer rig jacknifed about 8:30 a.m. on the icy road, causing 19 cars behind it to slide and bump into each other. Parts of southbound 1.95 between Rte 216 and Rte. 32 were closed for up to two hours creating a massive traffic backup. Police said there were no injuries.

Other suburban areas also reported treacherous roads, and commuters reported taking 30 to 60 minutes longer than usual to get to work.

On 1-66 near the Rte. 123 exit in Fairfax County, incoming traffic was halted by two jacknifed tractor trailers and had to make a detour.

Harsh weather conditions also prevailed elsewhere in the nation.

Hurricane-force winds buffeted Cape Cod. High winds knocked over a radio transmission tower in Bridgeport, Conn. Gale warnings were issued for Chesapeake Bay and the adjacent Atlantic Ocean.

Huge ocean swells from a north Pacific Ocean storm battered parts of the California coast, endangering expensive beachfront homes.

The cold front that hit Washington early yesterday also moved into the Deep South, bringing freezing temperatures to Louisiana and southern George. The front was preceded by tornadoes and high winds in Florida where one man was killed and 23 persons injured Sunday, according to the Associated Press.

The National Weather Service issued freeze warnings for Florida's citrus areas as far south as the Everglades for early today.

Heavy snow and subzero temperatures hit much of the Midwest. Up to 14 inches of snow in Ohio and a foot in northern Indiana were reported yesterday. Scores of highways were closed. Hundreds of schools closed from the Great Lakes to Tennessee.

Closer to Washington, show fell a foot deep in parts of Southwest Virginia. The Blue Ridge Parkway in Virginia and North Carolina was closed.

Snow accumulation tapered off in central and Northern Virginia with only an inch or two reported in most Washington suburban areas. Treacherous roads caused some suburban schools to be closed early.

The National Weather Service measuring station at National Airport recorded an official 0.6 inches at noon yesterday.

A weather service forecaster said the snow first started falling at the airport at 5:40 a.m. and stopped at 11:21 a.m. The snow during the weekend which totaled more than an inch.

Minor flooding on some streams including the Monocay River near Frederick. Md., was also reported. The Potomac River.which had been flowing slightly below the normal early January rate of 7.4 billion gallons a day yesterday. It is expected to crest today at 1 p.m. but well below flood stage, according to weather service river forecaster Leo Harrison.

More dramatic was the sudden drop in temperature here early yesterday as the cold front swept through. The thermometer at Naitonal Aiport stood at a blamy 62 degrees at 2 a.m. At 2:10, the wind suddenly shifted, and the leading edge of the cold front hit the area. By 3 a.m., the temperature had fallen to 44.

Thereafter, it dropped more slowly, hitting the freezing mark of 32 degrees at 9 a.m. It leveled off at 25 degrees from noon until 4 p.m. Then, as the sun disappeared, the temperature began to plunge toward the teens.

Because of the unseasonably warm weekend, road surfaces had heated up and were slow to freeze yesterday morning despite the subfreezing air, thus averting even worse conditions for the rush hour.

Forecasters described the cold front as "unusually strong" and "well defined." This created sharp temperature differences among cities along the East Coast as the front moved slowly eastward. At 2 p.m. yesterday, for example, the temperature here was 25 degrees, but in Boston, which had not yet been hit by the front the thermometer read 53 degrees. At the same time, it was 15 degrees in Atlanta, 600 miles south and west of Washington.

A number of motorists including several taxi drivers complained yesterday that the main roads in the District of Columbia did not appear to have been sanded by road crews. But Paul Weber of the D.C. Transportation Department's snow emergency center said by 5 a.m., spreading rock salt, and that by 9:35 a.m., 87 spreader crews were working.

Another department spokesman said later in the day that all major commuter routes in the city had been treated with rock salt.

Weber said the city was alerted to the snow squalls late Sunday night by Accu-Weather, Inc., of University Park, Pa., a private weather consultancy which provides regular forecasts on a contract basis for the city.

"We had staff come into the snow emergency center (222 Massachusetts Ave. NW) at 1 a.m. to start monitoring the situation" and to prepare for snow clearing operations, Weber said.

Suburban areas also reported spreading large amounts of rock salt or sand on roads. In Montgomery County, 18 crews were assigned at 6:30 a.m. to spread rock salt on 460 miles of main arteries, according to Hartwood Cornell, assistant operations chief of the county transportaion department.

In Prince George's County, Bill Boyce, chief of the roads and bridges division, reported that crews spread about 400 tons of rock salt over 650 miles of roads.

Metro officials reported no serious problems with either buses or subway trains throughout ther area.

The wind-damaged office building under construction in Fairfax City is located at 4103 Chain Bridge Rd. Under strong gusts of wind, the partly completed top three stories of the five-story structure collapsed at about 9:30 a.m. The three stories consisted of steel girders and corrugated metal sheeting.

The car crushed by a falling tree in Gaithersburg was parked in the unit block of Holly Drive. Residents of the block said a nearby house was grazed but not severely damaged by the tree.