More than 300 Boy Scouts (search) were sickened by the heat Wednesday while waiting for President Bush to arrive at a memorial service for four Scout leaders who were killed while pitching a tent beneath a power line.

The president's visit to the Scout Jamboree (search) at Fort A.P. Hill was postponed because of the threat of severe thunderstorms and strong winds. Instead, Bush is scheduled to visit the gathering Thursday.

But before the president's appearance was called off, many Scouts fell ill from temperatures that rose into the upper 90s, made worse by high humidity.

Half of those were treated and released from the base hospital, about three miles from the event arena. Dozens more were sent to other hospitals, where they were in stable condition Wednesday night, said Gregg Shields, a Jamboree spokesman.

Soldiers carried Boy Scouts on stretchers to the base hospital, and others were airlifted from the event.

Jamboree officials called for emergency assistance from surrounding areas, and ambulances transported Scouts during a storm that brought high winds and lightning.

Jamboree spokeswoman Renee Fairrer said she was not sure if any of the illnesses were serious. "If there are any, I haven't heard about them yet," Fairrer said.

The gathering has drawn more than 40,000 Scouting enthusiasts from around the world to the fort about an hour south of the nation's capital.

The memorial service had been planned to honor four men who were electrocuted Monday while pitching a dining tent at the Jamboree.

On Wednesday, a spokesman said the group had ignored scouting teachings by putting the tent under a power line.

The Scout leaders also had taken the "somewhat unusual" step of hiring a contractor to help with the task, Scouts spokesman Gregg Shields said.

"Boy Scouts are taught not to put their tents under trees or under power lines. I don't know what happened in that case," Shields said.

Some Scouts witnessed the deaths of the leaders as the large pole at the center of a large, white dining tent came into contact with power lines. Screams rang out as the tent caught fire and the men burned.

An investigation into the accident is incomplete.

While power lines crisscross the Jamboree's 7,000 acres, the leaders of Western Alaskan Troops 711 and 713 had ample room to erect a tent out of range of overhanging limbs and power lines.

The Jamboree is divided into subcamps, each of which is responsible for putting up a mess tent for what could be the hundreds of Scouts in their division. Shields said he did not know if Scouting has a specific policy regarding the proximity of tents to power lines, and he could not identify the contractor hired by the Alaska troop.

Flags flew at half-staff near the shooting range Wednesday. Cameron Ogilvie, 15, of York, Pa., said he heard of the deaths from his bus driver as he was riding back to his campsite.

"It shocked all of the boys on the bus hard. We all just got quiet," he said.

Scoutmaster Brad Mohr (search), 51, of Pasadena, Calif, said an announcement after the accident informed leaders not to erect structures taller than 6 feet.

Those killed were Michael J. Shibe, 49, Mike Lacroix, 42, and Ronald H. Bitzer, 58, all of Anchorage, Alaska; and Scott Edward Powell, 57, who had recently moved from Anchorage to Perrysville, Ohio. Shibe had two sons at the Jamboree and Lacroix had one.

Three adults were injured, and one returned to the Jamboree after being released from the hospital.