Acting space agency administrator Alan Lovelace set April 10 as the official launch date for John Young and Robert Crippen on the first orbital test flight of the space shuttle Columbia. But he emphasized that the date could change. Mr. Lovelace adopted the date after a day-and-a-half review of all aspects of preparations for the 54 1/2-hour flight of America's first reusable spaceship. At the launch pad, technicians completed loading hazardous turbine fuel aboard the space shuttle. The operation was nearly a day behind schedule , but Lovelace said the countdown should still begin Sunday.