* Sandy expected to make landfall Monday night
* Sandy's large wind field a record maker
* Storm may halt, flood New York City subway system
(Updates storm position, flood details)
HATTERAS ISLAND, N.C., Oct 28 (Reuters) - Hurricane Sandy could be the biggest storm to hit the United States mainland when it comes ashore on Monday night, bringing strong winds and dangerous flooding to the East Coast from the mid-Atlantic states to New England, forecasters said on Sunday.
Sandy could have a brutal impact on major cities in the target zone like Boston, New York, Washington, Baltimore, Philadelphia, one of the most densely populated regions of the country and home to tens of millions of people.
``The size of this alone, affecting a heavily populated area, is going to be history making,'' said Jeff Masters, a hurricane specialist who writes a blog posted on the Weather Underground (www.wunderground.com).
Forecasters said Sandy was a rare, hybrid ``super storm'' created by an Arctic jet stream wrapping itself around a tropical storm, possibly causing up to 12 inches (30 cm) of rain in some areas, as well as heavy snowfall inland.
Government officials in several states in Sandy's path faced tough decisions on emergency plans, including mandatory evacuations in vulnerable coastal areas, and residents scrambled to buy supplies before the storm comes ashore on Monday night.
New Jersey Governor Chris Christie ordered the state's casinos to close by 4 p.m. and began preparations in case the state had to shut down its bus and rail systems.
On its current projected track, Sandy is most likely to make landfall between in the New York/New Jersey area and head inland to Philadelphia and Pennsylvania, forecasters said.
EXCEPTIONALLY WIDE STORM
Forecasters at the National Hurricane Center in Miami said it was too early to predict precisely where the storm would make landfall but the impact would be felt far from the center.
While Sandy's 75 mph (120 kph) winds were not overwhelming for a hurricane, its width made it exceptional. Hurricane-force winds extended 175 miles (280 km) from its center while its lesser tropical storm-force winds spanned 1,040 miles (1,670 km) in diameter. It was not expected to strengthen but was expected to broaden.
In New York City, officials discussed whether to shut the subway system on Sunday in advance of the storm, which could bring the country's financial nerve center to a standstill.
At high tide, the storm could bring a surge of seawater up to 11 feet (3.4 meters) above normal levels to Long Island Sound and New York Harbor.
``Given the large wind field associated with Sandy, elevated water levels could span multiple tide cycles, resulting in repeated and extended periods of coastal and bayside flooding,'' the forecasters said.
The storm could cause the worst flooding Connecticut has seen in more than 70 years, said the state's governor, Dannel P. Malloy.
Sandy was centered about 260 miles (420 km) southeast of Cape Hatteras, North Carolina, early on Sunday, the hurricane center said.
The storm was moving over the Atlantic parallel to the U.S. coast at 10 mph (17 kph), but was forecast to make a tight westward turn toward the U.S. coast on Sunday night.
Tropical storm conditions were spreading across the coast of North Carolina on Sunday morning and gale-force winds are forecast to begin affecting Washington, New York and southern New England by Monday.
In Brussels, European air traffic control agency Eurocontrol warned of disruption to flights to and from Europe from Sunday evening.
Sandy could be the largest storm to hit the United States, according to the National Oceanic and Atmospheric Administration's (NOAA) website.
Sandy killed at least 66 people as it made its way through the Caribbean islands, including 51 in Haiti, mostly from flash flooding and mudslides, according to authorities.
The approaching storm forced a change of plans for both presidential candidates ahead of the Nov. 6 election. The White House said President Barack 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 rescheduled campaign events planned for Virginia on Sunday and was flying to Ohio instead.
All along the U.S. coast, 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.''
(Additional reporting by Dave Warner in Philadelphia, Ellen Wulfhorst in New York, Mary Ellen Clark and Ebong Udoma in Connecticut and Sam Youngman in Washington; Writing by Jane Sutton and David Adams; Editing by Sandra Maler)