The Loudoun County Sheriff's Office is investigating an incident this week at the county jail in which a Reston man slipped into a coma after his arrest on cocaine-related charges.

Darryl Jackson, 23, was sent to the jail instead of a hospital Monday, even though Leesburg police say they saw Jackson chew on rocks of crack cocaine during his arrest in Leesburg.

Jackson was still in a coma yesterday and listed in critical condition at Loudoun Hospital Center.

Sheriff John Isom ordered an investigation of the incident because Jackson had seizures and lost consciousness at the county jail, which is operated by the sheriff, a spokeswoman said.

"Since Jackson displayed signs of illness while awaiting the placement of charges, we are interviewing our employees to determine exactly what occurred . . . at our facility," said Deputy Carol Showalter.

Leesburg Police Chief James Kidwell said the senior arresting officer, Capt. Michael McVeigh, followed proper procedure in sending Jackson to jail because he had shown no signs of medical trouble.

"If somebody needs medical care, the officer makes sure he gets medical care," Kidwell said, describing the department policy.

Police said three officers approached Jackson about 4 p.m. Monday in the Plaza Street Park near Loudoun House Apartments and asked him for identification, McVeigh said.

According to McVeigh, Jackson then hit one officer, tried to run and started chewing on the cocaine derivative, McVeigh said. After a struggle, police removed a "pretty large rock of crack" from Jackson's mouth and asked Jackson if he had swallowed any of it, McVeigh said.

After Jackson denied swallowing any crack, and because he was resisting arrest, police decided to send him to the jail, McVeigh said. "I thought it was better for him to go to the jail than to the hospital at that point," he said.

Police called for a car at 4:09 p.m. Jackson arrived at the jail at 4:23 p.m., Showalter said. A rescue squad was called at 4:45 p.m., when Jackson began shaking and fell to the floor of a holding area, Showalter said.

After being treated at the scene, Jackson was taken to Loudoun Hospital Center and admitted at 5:20 p.m., said Pete Plasmier, a Loudoun County emergency dispatcher. Hospital officials said Jackson is in the intensive care unit.