The death of two women in September by a bolt of lightning in Hyde Park was caused by their underwire bras acting as conductors, a coroner said today.

''I think this was a tragic case, a pure act of God,'' the coroner, Paul Knapman, said at an inquest into the deaths.

The women, Anuban Bell, 24, and Sunee Whitworth, 39, had sought shelter under a tree during a thunderstorm on Sept. 22.

Dr. Iain West, a pathologist, said the women had burn marks on their chests from the current.