John Pfeil of Reston easily won the Herndon 10-Mile Run yesterday, which went off without any difficulties after officials took a number of precautions to safeguard the runners from problems with the heat and humidity.

In last year's race, under nearly identical weather conditions, two runners collapsed and died. Henry J. Kronlage, an IBM engineer from Fairfax County, wandered off into some heavy underbrush after finishing the race and died of heat stroke. Patrick Reiley, an Arlington County schoolteacher who had not run many races, was found in some woods 300 yards from the course. He had suffered a heart attack.

Today's pared-down field of about 360 covered the course uneventfully, under the watchful gaze of more than 100 race monitors, policemen and paramedics. The only mishap reported was a groin pull.

Pfeil, a computer programmer, averaged better than 15 miles an hour most of the race, never losing the lead. He finished in 53 minutes 10 seconds. Pete Chander of Fairfax came in a minute later to take second. Mary Ellen Williams of Rockville was the first woman, finishing in 64:27.

When the runners set out from the Herndon Community Center about 8:30 a.m., the temperature was 72 degrees and the relative humidity was 56 percent. By 10, when most of the runners crossed the finish line, the temperature was rapidly climbing past 85 to 90, and the relative humidity had risen to 79 percent.

The temperature last year when the field of 650 took off at 9:15 a.m. was 82 degrees. It rose to 88 by noon.

No one was left alone long enough today to have any difficulty go unnoticed. At nearly every turn on the course through town, residents sprayed runners with garden hoses. Runners were given cups of water almost every half-mile, and paramedic crews were stationed at the five-, seven-, eight- and nine-mile checkpoints.

Besides having more monitors, race officials altered the course so it would run through the shadier residential streets. They also required all runners to sign a statement saying they had completed a 10-kilometer (6.2-mile) race in the last 60 days.

"The people who set this up went all out to make sure there was no trouble. They did more than they had to," said Chuck Havill, 40, of Great Falls. "There were a lot fewer people here today, but it was a much better crop of runners. The Sunday jogger didn't come out because his wife wouldn't let him, after last year."

"They took a lot more precautions this year," added 52-year-old Charlie Gore of Silver Spring. "Last year they just got out and said, 'Go, gang.' "