The Boy Scouts marched onto the field singing, plopping down in the grass to wait for President Bush. But hours later, the news that Bush couldn’t make it was drowned out by sirens and shouts as hundreds fell ill because of the blistering heat.

About 300 people, most of them Scouts, suffered from dehydration, fatigue and lightheadedness Wednesday — just days after four Scout leaders were killed at the national Jamboree while pitching a tent beneath a power line.

Temperatures at Fort A.P. Hill, an Army base where the 10-day event is being held, reached the upper 90s and were intensified by high humidity.

“This is hot for me,” said Chad McDowell, 16, who lives in Warrenton, Ore. “Where I’m from if it’s 75, we think that it’s a heat wave.”

Half of the 300 who fell ill were treated and released from the fort’s hospital. Dozens more were sent to surrounding hospitals, where they were in stable condition Wednesday night, Jamboree spokesman Gregg Shields said.

The more than 40,000 Scouts, volunteers, and leaders attending the event had been standing in the sun about three hours when word came that severe thunderstorms and high winds were forcing the president to postpone his appearance until Thursday. Bush’s spokesman said Thursday that the visit would instead happen Sunday, at the Scouts’ request.

Repeated phone calls to the Jamboree press office were not returned.

Bush missed last Jamboree

At the last jamboree four years ago, Bush’s trip was also canceled because of bad weather, in which lightning strikes caused minor injuries to two Scouts. He spoke to the group a day later by videotape.

This time, Bush was expected to talk about the importance of Scouting and touch on the Monday deaths of four Scout leaders.

Many Scouts ate dinner at 2 p.m. and stood in long security lines to get a good spot in the open field to see what for most would be their first glimpse of a president in person.

Volunteers distributed water and ice by the caseload, and the Scouts were told they could remove their uniform shirts if they had another shirt underneath — a rarity for an event as important as a presidential visit, most Scouts said.

Soldiers carried Scouts on stretchers to the base hospital, located about three miles from the arena stage. Others were airlifted from the event while Jamboree officials called for emergency help from surrounding areas to transport Scouts during the storm, which brought high winds and lightning.

The illnesses came as many were still reeling from the deaths of four Boy Scout leaders from Alaska. Some Scouts had been watching as the metal pole at the center of a large, white dining tent touched power lines. Screams rang out as the tent caught fire and the men burned.

Three victims from Alaska

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.

On Wednesday, Shields said the group had ignored scouting teachings by putting the tent under a power line and leaders had taken the “somewhat unusual” step of hiring a contractor to help with the task.

“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.

An investigation into the accident was incomplete.

Scott Cameron, 57, of Anchorage, volunteered to fill in as a troop leader after the accident. He said the Scouts are getting through their grief.

“We’ll be fine for a minute and then just break down,” he said. “But we’ve had an awful lot of help.”