GRAND PRAIRIE, Texas — A medical transport service overcharged the federal government nearly $2 million for evacuating sick or injured people during hurricanes Katrina and Rita, government auditors say.

CareFlite billed the Department of Health and Human Services $5.7 million for transporting 810 patients in six months.

The government says the contract called for CareFlite to arrange transportation "in the most economical fashion, using subcontractors if necessary."

The audit by the HHS inspector general's office said there were times when the Grand Prairie company used its own aircraft when it could have looked for less expensive transportation. The average cost for patient transport when CareFlite used its own plane was $18,200. For subcontractors, the average cost was $7,783, the audit said.

Both CareFlite and the Health and Human Services Department defended the costs, saying the contract didn't require CareFlite to seek subcontractors with lower rates.

The audit recommended HHS work with CareFlite to determine how much can be allowed of $1.97 million that was billed without seeking subcontractors.

However, Martin J. Brown, HHS deputy assistant secretary for acquisition management and policy, said the agency saw no reason to challenge the amount that CareFlite charged.