In 1972, the only copy of a 400-page uncompleted manuscript was
stolen from the front seat of Sharon Kay Penman's automobile.
The shock was such that she could not write another word for the
next five years. But she eventually started over, and next month
Holt, Rinehart & Winston will publish her 928-page novel of
Richard III, ''The Sunnein Splendor.''  Budd Schulberg had
better luck with his first novel. Returning to his hotel soon
after he arrived in New York years ago, he discovered to his
horror that he had lost the only copy of his completed
manuscript of ''What Makes Sammy Run?''  ''I nearly went mad,''
he recalled. ''I told myself if it's lost for good I'm going to
quit writing.'' Instead, he began to retrace his every step that
day. ''Finally I went back to a stationery store on Madison
Avenue and there was the proprieter reading it,'' he said. Since
then, Mr. Schulberg sends copies of everything he writes to his
agent, his sister and occasionally to friends.  Like Miss
Penman, other writers have not