Criminal charges have been dropped against Harry B. Ellis Jr., the Washington executive whose assistant office manager drowned when he threw her off his yacht during an afternoon outing on the Chesapeake Bay with his friends and colleagues.

Annapolis police charged Ellis, the 57-year-old head of a Washington consulting firm, with manslaughter in the June 27 drowning of Theodoris Scott. But Maryland Assistant State Attorney David Plymyer said yesterday, "We're not going to proceed with prosecution of this case. The evidence wasn't adequate to show that an act was done in reckless disregard of human life."

There were 23 passengers aboard Ellis's boat that day. Clarence Scott, 30, husband of the victim, had said that he told Ellis his wife couldn't swim. It had been her first time on a boat, he said. But others aboard the yacht said that Ellis didn't know Mrs. Scott, who was the mother of a 5-year-old girl, was a nonswimmer.

Plymyer said his office interviewed 24 witnesses in the case. "He certainly threw Mrs. Scott over the side of the boat," he said. "But the evidence doesn't establish that he was warned she couldn't swim. No one, including the victim, told him she couldn't swim."