The site of the National Boy Scout Jamboree was closed to outsiders Tuesday for a safety review and to give tens of thousands of Scouts the chance to grieve for four adult leaders who were electrocuted as they set up camp on the event's opening day.

The Scouts tried to go about the regular activities of the Jamboree, which is held here every four years and attracts youngsters from across the country and throughout the world. Investigators, meanwhile, tried to determine how the accident occurred.

As Scouts roamed their tent city, heading for archery ranges and scuba pools, leaders said the deaths had cast a pall over the beginning of what was supposed to be 10 days of pure fun. Yet they vowed the event would continue as planned.

Military officials closed Fort A.P. Hill to visitors, citing extreme heat, threats of lightning and the need to give Scouts time to deal with the deaths, which Boy Scouts national spokesman Gregg Shields called the organization's "worst disaster" in the 68-year history of jamborees.

After a brief news conference at the base, reporters were asked to leave, and Scout leaders at the Jamboree and across the country were told not to comment on the incident. Army Maj. Vince Mitchell, a public affairs officer with the First U.S. Army, which oversees military forces at the Jamboree, said the accident had prompted a basewide review of safety procedures.

Shields gave no further information about how Monday's accident happened, saying only that it occurred as the leaders -- with troops from western Alaska looking on -- erected a large canopy that was to be used as a dining area.

He also identified the Scout leaders who were killed: Ronald H. Bitzer, 58, Michael J. Shibe, 49, and Mike Lacroix, 42, all of Anchorage; and Scott E. Powell, 57, who recently had moved to Perrysville, Ohio.

Four others were hurt in the accident, including a Scout who was treated for minor injuries, Shields said. Two -- Anchorage Scout leader Jay Lawrence Call, 43, and a contractor who has not been identified -- were in stable condition at Virginia Commonwealth University Medical Center in Richmond. Another contractor was treated and released, Shields said.

Shibe was with two sons at the Jamboree, and Lacroix was with one, Shields said. The three boys were on their way home to Alaska on Tuesday, he said.

A memorial service for the leaders who were killed is planned for Wednesday, Shields said. President Bush is still expected to speak to Scouts at a kickoff show Wednesday night, he said.

Shields said Scouts had been informed of the deaths in the Jamboree's daily newspaper and by its radio station, both of which are run by Scouts. He said some troop leaders had met with their Scouts to speak about the tragedy.

Yet some Scouts seemed to have been left in the dark, getting information only by word of mouth -- which, in some cases, spiraled into tales that Scouting officials insisted were untrue.

"What accident?" one boy at the Jamboree asked another after being told reporters were on base to cover an accident.

"Five kids got electrocuted," his friend responded.

Later, four members of a Scout band who roamed downtown Fredericksburg after a performance Tuesday afternoon said they had heard that there had also been two heat exhaustion deaths at the jamboree. Some said they were told the electrical accident occurred when a truck hit a telephone pole, causing it to fall on camp showers.

Shields said that there were no deaths from heat exhaustion and that authorities did not believe a vehicle was involved in the electrical accident.

The Scouts in Fredericksburg said the jamboree's sad start had not quashed their expectations of an action-packed week. They noted that the jamboree, which drew more than 40,000 Scouts and leaders, amounted to a small city -- and that they saw the deaths as something to be expected in such a place.

"No one's hit really, really hard except for those troops" from Alaska, said Andrew Townsend, 16, a Scout from American Fork, Utah.

On the Jamboree radio station, QBSA, Scout disc jockeys also seemed focused on getting on with the campout, offering upbeat announcements -- deadlines for science projects and reminders about rappelling opportunities -- and songs by the Village People and Coldplay.

Jamboree activities at Fort A.P. Hill, Va., continue as an investigation into the deaths of four adults Monday is ongoing.Scout leaders and volunteers, including Don Dare of Knoxville, Tenn., right, attend a news briefing on the deaths of four adults at the Jamboree.