A package arrived at the Waldorf-Astoria here on Park Avenue the other day containing a delicate 5 1/2-inch silver oyster fork, estimated to be 65 years old.

It had been "fliched," as the management diplomatically terms it, at least half a century ago from the old Waldorf-Astoria that stood on the site now occupied by the Empire State Building. Along with the fork was a neatly typed letter.

"Dear Sirs," it said. "While cleaning my aunt's silver I came across this piece. She is too forgetful to tell me how it came to be in her silver chest. How I would love to know who took it for a 'souvenir' and when. But I guess we will never know . . . Nonetheless, it is 'stolen goods,' hereby returned."

Within a day another package arrived containing a knife. The handwritten letter accompanying it was couched in bluntly honest terms: "Enclosed you will find a silver table knife that I stole about 25 years ago from the Waldorf." The writer went on to say he had accepted Jesus Christ as his "personal savior."

Since Jan. 28 of this year when silver prices peaked at record highs more than $30,000 worth of "pilferware" has been returned, according to Waldorf manager Eugene R. Scanlan.