* Record temperatures expected from St. Louis to Washington
* Utilities working to restore power after weekend storms
* Power restoration seen taking several days
* 288 heat records set on Sunday - weather service
By Ian Simpson
WASHINGTON, July 2 (Reuters) - Relentless heat gripped much of the eastern United States for a fourth straight day on Monday, with nearly 2 million homes and businesses without power after violent storms and soaring temperatures killed at least 18 people.
Power companies warned it could take several days to restore electricity completely in some areas as much of the United States sweltered in a heat wave. On Sunday, 288 temperature records were set nationwide.
"Above-normal temperatures will continue to affect a large portion of the country from the northern Plains to the Mid-Atlantic over the next few days," the National Weather Service said.
Severe thunderstorms, strong winds and hail ripped down trees and power lines in northern Minnesota, knocking out the phone system in the city of Bemidji and soaking Duluth, authorities said.
"It's quite a big wind event," said Dave Kellenbenz of the National Weather Service in nearby Grand Forks, North Dakota.
Storms also struck in southern Illinois, Kentucky and Tennessee, the weather agency said.
Many areas will see temperatures from 90 Fahrenheit (32 Celsius) to more than 100 F (37.7 C), it said in a statement. Excessive heat warnings and advisories remained over much of the mid-Mississippi Valley and southern states.
Emergencies were declared in Maryland, Ohio, Virginia, West Virginia and Washington because of damage from a rare "super derecho" storm packing hurricane-force winds across a 700-mile (1,100-km) stretch from the Midwest to the Atlantic Ocean.
Nearly 2 million homes and businesses from Illinois to New Jersey were still without power, with the biggest concentration in the Washington area.
With power lines down across the region, the U.S. government told federal workers in the Washington area they could take unscheduled leave or work from home on Monday and Tuesday.
Two of the largest property insurers, USAA and Nationwide, said they had received more than 12,000 claims in total from the weekend storms. Most were for house damage.
The storms capped a costly June for insurers, which were already facing losses of at least $1 billion from a hailstorm that ripped through Dallas.
Thunderstorms and high winds battered eastern North Carolina on Sunday afternoon, causing three more deaths on top of at least 15 from deadly storms and heat in several states.
About 93,000 customers in northeastern Illinois of Commonwealth Edison, a unit of Exelon Corp, were without power from the storms that brought wind gusts of up to 90 miles per hour (145 km per hour).
Utilities in Ohio, Virginia and Maryland described damage to their power grids as catastrophic.
FirstEnergy utilities in states from Ohio to West Virginia had about 194,400 customers without power.
Pepco, which serves Washington and much of its suburbs in Maryland and Virginia, reported about 201,900 customers without power.
Baltimore Gas & Electric said about 213,000 customers remained affected. Almost 1,200 utility workers from 12 states and Canada are helping restore power or are on their way to central Maryland, the company said.
Storms killed six people in Virginia and left more than 1 million customers without power. Two people were killed in Maryland, officials said.
A falling tree killed two cousins, aged 2 and 7, in New Jersey. Heat was blamed for the deaths of two brothers, ages 3 and 5, in Tennessee who had been playing outside in temperatures reaching 105 F (41 C).
St. Louis reported three heat-related deaths over the weekend. All were elderly and had air conditioners not in use.
Meanwhile, soybean and corn crops in the U.S. Midwest are expected to get hit hard by the unrelenting heat and dryness. Corn, which is entering its critical pollination or reproductive stage of development, is seen as especially vulnerable.
"We're still looking at a scenario providing below-average rainfall for at least the next 10 days," said agricultural meteorologist John Dee of Global Weather Monitoring.
AccuWeather, a weather forecaster, said the "super derecho" storm that caused the widespread damage had raced 700 miles (1,260 km) from northern Indiana to the Atlantic coast in 12 hours.
A derecho - Spanish for "straight" - is a long-lasting wind storm that accompanies fast-moving thunderstorms or showers, AccuWeather said. The most powerful derechos are called "super derechos," described by AccuWeather as a "land hurricane."