With another snowstorm bearing down on Baltimore, officials called on local contractors and out-of-state equipment for help, warned that stretches of some highways could be shut down today and implored area residents to stay home.

Forecasts calling for 10 inches to 20 inches of snow sparked a new round of cancellations and closings. State offices and the federal government, area schools and some businesses will be closed. Flights at the airport probably will be halted, and the mail isn't likely to get delivered.

State officials say they are running low on salt in some areas and crews are exhausted from a days-long run, but Gov. Martin O'Malley said everyone needs to be ready again. Utility crews were working Tuesday to get the last homes without power - fewer than 6,000 statewide - back online. State transportation workers were pushing snow onto road shoulders and outside lanes, to make room for what's next.

"We have been gearing up all day," said O'Malley during an afternoon news conference, adding that the bill so far to keep roads clear has been $35 million.

Neil Pedersen, state highway administrator, said the state will close roads if they appear dangerous or impassable. Officials do not want a repeat of last weekend's traffic backups caused by disabled cars and jackknifed trucks. He noted that no fatalities have been attributed to the storm, but there have been many crashes, mainly from people driving too fast.

"We're using all our equipment and contractor equipment, including a number of pieces from out of state," Pedersen said. "This storm will make things more difficult because we have no more room to store the snow."

Road clearing has been a challenge because the snow has become icy and clings to the ground. Crews have been using heavy equipment, including front-end loaders and graders, to break it up and push it back from middle lanes. Six-lane roads are down to four, and four-lane roads are down to two.

The state has 2,700 workers to clear some 17,000 miles of numbered roads, including all the major highways, according to the State Highway Administration. Some equipment to break up ice has been brought in from New York.

Crews have about 180,000 tons of salt left from the seasonal stockpile of about 350,000 tons. Some of that has been moved from the Eastern Shore, where accumulation is expected to be less than in metro Baltimore, and distributed to counties where supplies have run low. Some will be mixed with sand to make it last.

But it will still take days to dig out from the third major storm of the season.

Beverley K. Swaim-Staley, the state transportation secretary, said crews were also working to keep light rail and buses moving. They have been running on a limited basis, but service is likely to fall off even more as tracks and roads deteriorate.

At Baltimore- Washington International Thurgood Marshall Airport, airlines began canceling flights Tuesday afternoon. Jonathan Dean, airport spokesman, said 350 employees and contractors with 200 pieces of specialized equipment will be working to keep the runways open as long as possible.

Crews will also work to keep taxiways, roads and lots clear. They brought in machines that can melt big piles of snow because there isn't enough space at the airport to store it.

This all will enable flights to resume quickly. "We'll work overnight [Tuesday], even if all service is canceled, which appears likely," Dean said, advising travelers to contact their airlines.

Also trying to get through are the mail carriers. Yvette Singh, a U.S. Postal Service spokeswoman, said carriers have been instructed not to deliver mail in dangerous conditions, which meant no mail on Saturday and limited mail this week. Officials planned to assess the snowfall this morning before calling off carriers for the day, but she said, "It's not looking good." In the meantime, she asked that residents shovel driveways, sidewalks and paths to mailboxes for the carriers.

Those who tried to fill up their cars before the new storm found gas in short supply in some places. Deliveries were a problem for some stations, and a power outage at a major terminal in the region limited its ability to fill tankers, said Paul Fiore, director of government affairs for the Washington- Maryland- Delaware Service Station Association.

In Baltimore, Mayor Stephanie C. Rawlings-Blake called for contractors with heavy equipment such as bulldozers to come forward. The Transportation Department also was trying to bring in more snow-melting and snow-moving equipment from out of state.

She said the city had been trying to clear secondary streets ahead of the new storm, but it planned to focus on major roads once the snow really started coming down. She also opened two emergency shelters for residents displaced by fire or other disasters. Inspectors planned to look at 400 structures that could collapse.

Anne Arundel County Executive John R. Leopold has activated the Emergency Operations Center in Glen Burnie to handle calls from residents. The county's 284 plows have been on the streets with county workers and private contractors working 12-hour shifts since Friday.