Heavy snow from a major winter storm was falling throughout the area early today, and with four inches on the ground in places by 1 a.m. and a total of eight inches expected, prospects for this morning's rush hour appeared uncertain.

Hundreds of sand and salt trucks and snow plows rumbled over area roads and streets last night in an effort to keep roads clear, while D.C. officials towed 87 cars from principal arteries in the city and ticketed more than 500 in the three hours after a snow emergency declaration took effect at 10 p.m.

But although highway officials around the area dispatched fleets of trucks to plow snow and melt ice, their efforts to clear roads by morning rush hour were hampered as snow continued to fall heavily through the night.

A National Weather Service forecaster said late last night that he expected morning driving conditions to be hazardous. "We're advising people not to travel {by car} unless you have to," said National Weather Service forecaster Scott Prosise. "We're not telling people not to go to work. We're saying don't drive if you don't have to."

School officials in all jurisdictions said they would monitor the snowfall through the night and decide at 5 a.m. today whether to cancel classes or open schools an hour or two late. Federal officials, too, said they would wait until early this morning before deciding if and when government employees are supposed to report to work. Parents, students and workers are encouraged to tune in to early-morning radio or television broadcasts to hear reports on openings.

Metro transit officials said they expected all rail lines to remain in operation, although they said bus routes would be curtailed as road conditions dictated.

The National Weather Service said snow began falling in the western suburbs around 6:30 last night and was falling throughout the area by about 7:30 p.m. Three inches had fallen at Dulles International and National airports by 1 a.m.

Forecasters said the storm, which moved in from the south, could dump as much as six inches on the ground by 7 a.m. and that an additional inch or two likely would fall during this morning's rush hour.

Prosise said it appeared that strong winds and fast-falling snow would impair visibility, particularly in the hours before 7 a.m., while low temperatures would prevent melting of any snow and ice on the roads.

He also said the storm would cause achingly cold temperatures to hang on through the weekend. Temperatures yesterday, according to Prosise, dipped to 7 degrees at Dulles, rose to a "scorching 21" degrees by midafternoon and are expected today to hit "a heat wave high of 28" degrees.

But, he added, "The temperatures will be warmer but still below freezing, so, unfortunately, the snow will not be melting."

Metro officials said yesterday they were prepared for the expected snowstorm, although they have not received or installed all of the new snow removal equipment ordered after last year's storms crippled the transit system.

"If the snow occurs as forecast, we won't have any real problems," said John Egbert, Metro's deputy general manager and snow commander.

The major weapon in the new $28 million, three-year program to equip the system for heavy snow is electric heating tape to warm the third rail. Much of that equipment is not yet in place, but Metro has installed new switch heaters and remodeled most rail car motors to prevent blowouts. Officials said they planned to keep the cars running during the night to keep the rails warm and free of ice this morning.

Just the threat of snow sent Washington area residents scurrying to supermarkets, where there was such a run on milk, meat and other food items that some stores began running short.

"We've been real busy since opening at 7 a.m.," said John Gibbons, manager of a Safeway store in Southwest Washington. "I have government offices near me, and people who would normally be buying lunch are buying groceries."

Gibbons and managers at other stores said they were arranging for special deliveries to restock their shelves of some items.

The new snow was bad news for the homeless, who have begun filling the region's emergency shelters, and bad news for the poor in general, particularly those who rely on federal energy assistance.

At a news conference yesterday, the Salvation Army and Buyers Up, an energy group headed by consumer advocate Ralph Nader, warned that thousands of low-income families in the metropolitan area and more than 1 million families nationwide may face fuel shortages because of recent cuts in the Federal Family Services Administration budget.

"This budget cut leaves thousands of citizens without a safety net during one of the coldest winters on record," said Joan Claybrook, president of Buyers Up, who estimated that a 16 percent cut in the budget will force thousands of people here and in the rest of the country to be dropped from the energy assistance program this year.

To meet the expected shortfall, Claybrook and Maj. Robert Griffin, social service director of the Salvation Army's Washington Area Fuel Fund, issued a joint appeal for citizens to "contribute whatever they can" to the fuel fund, either by sending a check directly to the fuel fund or by making a donation on their next utility bill.

In Northern Virginia, highway crews were on "full alert" late yesterday afternoon in anticipation of a heavy snowfall, according to spokeswoman Marianne Pastor.

In contrast to past snow alerts, Pastor said, "Everyone is expecting we're really going to get hit this time. No one is holding out the hope that we're not going to."

Every since the heavy snowstorms last year that threw the city and its suburbs into chaos, local governments have been working to develop a coordinated approach to regional snow emergencies.

One key element concerns the Wilson Bridge, a notorious choke point even during fair weather. To eliminate the tie-ups that have blocked the bridge during previous snowstorms, Maryland and Virginia announced last month that they would station heavy-duty tow trucks at the bridge whenever heavy snow was forecast.

Cold weather kept most people indoors yesterday, but staying inside, according to James G. Rotton, professor of psychology at Florida International University in North Miami, can lead to the winter blahs.

"There is strong evidence that being stuck in the house and having your movement restricted makes people feel moody, down and depressed," said Rotton, who has studied the effect of cold weather on personality.

But Rotton had some good news for those who think they can't stand another day of the deep freeze.

"People facing a common threat, such as a snowstorm, are more likely to help each other," he said. "And the cold weather depresses the crime rate for obvious reasons -- people who commit crimes do not like to go out and get cold."

Staff writers Nell Henderson and Leah Y. Latimer contributed to this report.