Robert Paul Smith, 61, playwright and author, died Sunday in Mount Sinai Hospital in New York.

He was co-author with Max Shulman of the Broadway hit, "The Tender Trap," which later was made into a movie starring Frank Sinatra and Debbie Reynolds.

Mr.Smith was best remembered for his book of childhood recollections entitle, "Where Did You Go? Out. What Did You Do? Nothing."

In 1958, while appearing as a guest at one of The Washington Post's Book and Author Luncheons in connection with that book, Mr. Smith took advantage of the occasion to display some or the wit for which he had become known.

He provided an impromptu "Translations from the Washington," which he said he composed especially for the occasion. Some of the things Washingtonians mean, he said, when they say the things in parenthese include:

(A usually reliable source) "The shoes shine boy says . . ." (An informed source) "The barber says . . ." and (They say) "I say . . ."

Mr. Smith was born in Brooklyn, grew up in Mount Vernon, N.Y., attended the Horace Mann School for Boys and graduated from Columbia College, where he was co-editor of the Columbia Review.

He became a writer for the Columbia Broadcasting System and wrote four books, "So It Doesn't whistle," "The Journey," "Because of My Love" and "The Time and the Place," the last published in 1952.

"The Tender Trap" followed. In adition to "Where D2d Your Go? Out," Mr. Smith also wrote a number of other books later, including "How to Do Nothing with Nobody All Alone By Yourself" and "Translations from the English."

He is survived by his wife, Elinor Goulding Smith, two sons, Daniel Paul and Joseph Robert, a sister, and two grandchildren.