Marine searchers cutting through thick underbrush with machetes yesterday discovered the body of a second runner a half-mile beyond the finish line of Sunday's 10-mile foot race in Herndon.

Police said 49-year-old Henry J. Kronlage, an IBM engineer who lived in Fairfax County, apparently completed the race, then ran past dozens of onlookers at the finish line, through a gully, around a fence and over a hill before colapsing off a small path in dense woods 25 yards from a group of town houses.

Police said Kronlage apparently suffered heat stroke, which also apparently killed another contestant 31-year-old Patrick Reiley of Reston.

Reiley, an Arlington school teacher, was found dead Monday under a tree about 300 yards off the race course.

More than 100 volunteers, including a son of Kronlage, were involved in the two-day search, along with rescue personnel. Yesterday 50 Marines from the Quantico Marine Base joined the search after police found they were unable to penetrate thick foliage.

Police said they were led to the area where Kronlage's body was found after a local resident called to say she had seen a runner in the area on Sunday.

They say Kronlage may have been delirious when he missed a large sign pointing to the community center where the race ended, and then proceeded over an unmarked and difficult route to the point of his collapse.

Results of an autopsy on Reiley's body were not release yesterday. An autopsy is to be performed on Kronlage's body.

Herndon officials said they are analyzing the race to see what might have contributed to the deaths.

Officials of local running organizations yesterday joined medical authorities in criticizing the scheduling of the race.

They said the race should never have been held starting at 9:15 a.m. in Sunday's heat and humidity, although some other races are run around the country in similarly dangerous conditions.

Arthur A. Anselene, director of the town's recreation department, which sponsors the event, said race organizers knew the temperature Sunday morning exceeded 80 degrees but hesitated to change the starting time.

"It's very difficult to change a race once the time has been set," Anselene said.

"A summertime race of that length really should have started at 8," said Phil Stewart, president of the D.C. Roadrunners Club, who also participated in Sunday's race. "I had some misgivings and other people I talked to had misgivings about the race starting as late as it did.'"

Stewart said that as a result of the deaths, a 10-kilometer (6.2 miles) Roadrunners race scheduled for last night was changed to a "fun run" and that no times would be kept, to lessen the danger of a similar occurrence.

Race participants said this year's Herndon race was hotter than in the past because the course was moved from the 13,000-member community's neighborhoods to remote country. The new route lacked shade, as well as the generous dousings of water from spectators with hoses and sprinklers.

Anselene said yesterday the course was relocated because the number of runners had doubled each year -- to Sunday's 625 -- and that they were causing traffic problems.

Officials of running organizations said there are no hard and fast rules governing how and when races should be run, only guidelines. Such decisions are left to the judgment of local race directors.

No running organizations are affiliated with the Herndon event, although it is now in its fifth year and receives national publicity.

They say morning races are being held earlier and earlier in the day because of a growing awareness of heat stress problems, but that if guidelines set forth by medical organizations were applied to all races, some major competitions would not comply.

"The sport of distance running is pretty easygoing and not particularly rule oriented," said Darman. "There are marathons held in the summer, which I think is asinine. What surprises me is that thousands of people show up to run in them."

Two years ago, runners in a marathon in Chicago wore black arm bands to protest a change in the starting time from 8 a.m. to 10:30. They charged that the race organizers had purposely disregarded the runners' discomfort in favor of attracting larger crowds.

An 18-year-old runner claiming heat-related injuries is suing sponsors of the Peachtree Race in Atlanta, alleging they failed to warn him about the dangers and symptoms of heat stroke.