Two Fairfax County men disappeared yesterday morning during a 10-mile race in the western part of the county, and police said that by early today neither had been found.

The two men, one a 49-year-old IBM engineer, the other a 31-year-old teacher in the Arlington schools, vanished while running in the fifth annual Herndon 10-mile race.

A search for the missing men continued well into the early hours of this morning on the roads of both western Fairfax and eastern Loudoun counties on which the race was run.

Law enforcement officers from both counties joined Herndon town police and citizen volunteers in the search.

The missing engineer was identified as Henry J. Kronlage of 4532 Braeburn Dr., in the Rutherford community south of Fairfax City. He is the father of four children.

His wife, Nancy, told a reporter last night that she had not heard from him since he left early yesterday morning for the race, which was scheduled to begin at 9 a.m.

Mrs. Kronlage said her husband runs frequently and had entered the same race last year.

The missing schoolteacher, Pat Reiley of 2305 Freetown Ct., Reston, was running in his first race, according to his brother, Mike.

We're very worried," Mike Reiley told a reporter last night.

The two men did not know each other, relatives said.

From the center of Herndon, in the Northwestern part of Fairfax County, the race course proceeded west into nearby Loudon County, went over a little-used portion of the Dulles Airport grounds and looped around the Marriott Hotel at the airport before retracing the same route to Herndon.

More than 1,000 people reportedly entered the race despite temperatures that neared 90 degrees at race time, and the two missing men were spottted among them along the route, which included several checkpoints.

Kronlage was last reported seen at Rte. 606 and the airport access road. He wore yellow shorts, a bright green shirt and tan running shoes.

Reiley was last reported seen about 10 a.m. at Rte. 606 and the Loudoun County line. He was wearing blue shorts and a blue shirt.

The race was sponsored by the Herndon Department of Recreation.