NEW YORK (AP) _ Developer Donald Trump, nettled by a dispute over a small piece of Atlantic City real estate, wrote a scathing letter to self-styled hotel queen Leona Helmsley and denounced her as ''a disgrace to humanity.''

In a separate note to Mrs. Helmsley's husband, ailing real estate tycoon Harry Helmsley, Trump wrote, ''You are a great man who has been tarnished by, in my opinion, the actions of Leona.''

Trump's April 5 letter to Mrs. Helmsley began ''Dear Leona'' and was signed off ''Sincerely.'' It said in part:

''Over the last number of years I have watched as you have virtually destroyed my friend and a once-great and respected man, Harry Helmsley.''

''Without the veil of Harry Helmsley, you would be a nonentity. You would not be able to randomly fire and abuse people in order to make yourself happy. What has happened to the legendary Helmsley reputation is indeed sad - but I am not surprised because I know you so well.''

Mrs. Helmsley is an executive of her husband's company and appears in advertisements in which she styles herself ''The Queen'' of Helmsley hotels. She and her husband have been indicted on federal tax evasion charges.

Calls to the Helmsleys by The Associated Press on Wednesday were not returned immediately. Mrs. Helmsley was quoted in Wednesday's editions of the New York Post as declining to comment because of the pending criminal case.

Trump called her ''a disgrace to the industry and a disgrace to humanity in general.''

He said he decided to tell her off in writing when she refused to transfer to Trump the lease on a small Atlantic City, N.J., parcel that was part of a deal for a larger holding Trump bought recently from Penthouse magazine.

''I decided to write her a letter telling what a total disaster she is and what a disaster she's been to Harry,'' Trump said.