* Sandy expected to come ashore Monday night or Tuesday
* New York and New Jersey area could be hit first
* Sandy may halt, flood New York City subway system
* Mandatory evacuation in coastal Delaware communities
* Hurricane due to arrive a week before U.S. election
(Adds Obama campaign changes)
HATTERAS ISLAND, N.C., Oct 27 (Reuters) - Hurricane Sandy closed in on the United States on Saturday as coastal communities along the East Coast scrambled to prepare for torrential rains, high winds, major flooding and power outages a week before the presidential election.
Governors in states in the hurricane's path declared emergencies, announcing mandatory evacuations of vulnerable areas. New York City officials discussed whether to shut the subway system on Sunday in advance of the storm.
On its current projected track, Sandy could make U.S. landfall on Monday night or Tuesday morning anywhere between Maryland and southern New England, forecasters said. Some computer models show a likely landfall between Delaware and the New York/New Jersey area.
The hurricane was headed toward densely populated areas with tens of millions of people. Officials urged residents to stock up on food, water and batteries. Worried residents packed stores, buying generators, candles, food and other supplies in anticipation of power outages. Some local governments announced schools would be closed on Monday and Tuesday.
``They're freaking out,'' said Joe Dautel, a clerk at a hardware store in Glenside, Pennsylvania. ``I'm selling people four, five, six packs of batteries - when I had them.''
Sandy also threatened to disrupt air travel in the region.
Rain accumulations of up to 12 inches (30 cm) and heavy snowfall inland are considered likely in some areas. As it merges with an Arctic jet stream, forecasters said Sandy has all the ingredients to transform into a ``super storm'' unlike anything seen over the eastern United States in decades.
``There's no avoiding a significant storm-surge event over a large area. We just can't pinpoint who's going to get the worst of it,'' National Hurricane Center Director Rick Knabb said.
The White House said President Barack Obama took part in a call with U.S. Homeland Security Secretary Janet Napolitano and Federal Emergency Management Agency (FEMA) Administrator Craig Fugate to discuss preparations for Sandy.
The approaching storm forced a change of plans for both presidential candidates ahead of the Nov. 6 election. The White House said Obama canceled a campaign appearance in Virginia on Monday and another stop in Colorado on Tuesday, and will instead monitor the storm from Washington.
Republican challenger Mitt Romney canceled a trip to Virginia set for Sunday, when the state is expected to begin feeling Sandy's impact, and will go instead to Ohio.
Coastal flooding posed a major threat, particularly in low-lying areas like New York City, the global financial nerve center, and Alexandria, Virginia, across the Potomac River from Washington, D.C.
``This is not a coastal threat alone,'' Fugate told reporters, warning of the potential for flooding in Maryland and Pennsylvania, as well as more than 2 feet (0.6 meters) of snow in West Virginia and southwest Pennsylvania. ``This is going to go well inland,'' he added.
Delaware Governor Jack Markell ordered a mandatory evacuation of an estimated 50,000 people in coastal communities on Saturday. New Jersey's Cape May County ordered an evacuation of its barrier islands, home to some popular beach resorts, by Sunday afternoon.
In New York, authorities were considering closing down the city's buses, subways, commuter railroads, bridges and tunnels as early as 7 p.m. on Sunday, when the last commuter trains would depart, with the entire system to be closed down by 3 a.m. Monday, officials said.
Sandy was located about 330 miles (530 km) south of Cape Hatteras, North Carolina, and packing top sustained winds of 75 miles (120 km) per hour on Saturday evening, the Miami-based National Hurricane Center said. The storm was still moving slowly over the Atlantic at 13 miles per hour (20 kph).
Forecasters said flooding could span multiple tides with a storm surge of 4 to 8 feet (1.2-2.4 meters) in Long Island Sound, the southern portion of Lower New York Bay and Delaware Bay.
Sandy's storm surge has the potential to flood New York City's subway system if the storm arrives at or near Monday evening's high tide around 9 p.m., according to Jeff Masters, a hurricane specialist who also writes a Weather Underground blog.
Monday is also a full moon, which creates an extra-high tide. ``These storm surge heights will be among the highest ever recorded along the affected coasts, and will have the potential to cause billions of dollars in damage,'' Masters wrote.
Officials said 50 to 60 million people could be affected by Sandy, which many forecasters warn could be more destructive than Irene, which caused billions of dollars in damage across the U.S. Northeast in August 2011.
A GROWING STORM
Sandy continued to grow in size with tropical storm-force winds extending across 700 miles (1,125 km). More powerful hurricane force winds extended 105 miles (165 km) from its center, increasing the risk of downed trees and power lines, forecasters said.
``The winds... expected to be at or near hurricane strength at landfall... will spread inland for hundreds of miles either side of the storm center,'' according to a blog posted on Weather Underground (www.wunderground.com) by veteran weather forecaster Bryan Norcross.
``It's hard to imagine how millions of people are not going to be without power for an extended period of time,'' he added.
As the threat of a monster storm began to sink in, shoppers crowded hardware stores and supermarkets looking to stock up on emergency supplies. At a Trader Joe's store in Millburn, New Jersey, shelves were stripped bare of bread, bottled water and milk.
Customers at a Home Depot in Willow Grove, a suburb of Philadelphia, were greeted by big hand-written signs saying, ``No generators.'' The store received a shipment of 50 generators on Friday evening and sold them all within minutes of opening on Saturday, said January Introcaso, one of the store managers.
The store also sold out of flashlights and batteries. It was a similar story at other hardware stores in the area, with candles, tarps and rope also in demand.
Sandy claimed at least 59 lives as it made its way through the Caribbean islands, including 44 people in southern Haiti, mostly from flash flooding and mudslides, according to authorities. Another 11 people died in Cuba, largely due to from collapsed buildings, officials said.
Tropical storm-force winds were being felt near the North Carolina coast. There were tropical storm warnings for all of the coastal portion of the state, along with about half of South Carolina.
Along North Carolina's Outer Banks barrier islands, which jut out into the Atlantic, the winds and rains increased on Saturday, and ferry service between Ocracoke and Hatteras Islands on the Outer banks was suspended.
``Right now it's blowing pretty hard,'' said Ray Waller, manager of the Ocracoke office of North Carolina Ferry Division.
(Additional reporting by Dave Warner in Philadelphia, Ellen Wulfhorst in New York, Mary Ellen Clark in Connecticut and Sam Youngman in Washington; Writing by David Adams and Tom Brown; Editing by Will Dunham)