NEW YORK, APRIL 19 -- In what must rank right up there with Truman chewing out MacArthur and Sondra Gotlieb slapping her secretary, Donald J. Trump has shaken the onyx and marble foundations of the hotel world by calling his equally overpublicized rival, Leona Helmsley, a "disgrace to humanity." In a deliciously vitriolic letter to the self-proclaimed Queen of the Helmsley hotel empire, The Donald (as he is called by his relentlessly glamorous wife Ivana) displays a previously hidden capacity for venom by slicing The Leona into tiny little pieces. "Without the veil of Harry Helmsley, you would be a non-entity. You would not be able to randomly fire and abuse people in order to make yourself happy," The Donald declares in the letter, which mysteriously made its way into the pages of the New York Post today. "What has happened to the legendary Helmsley reputation is indeed sad -- but I am not surprised because I know you so well. When God created Leona, the world received no favors." Having castigated one spouse, Trump could not resist the chance to console the other. "Dear Harry," he wrote to Leona's husband. "You are a great man who has been badly tarnished by, in my opinion, the actions of Leona. I am enclosing a letter that I sent to Leona ... Regardless of what happens, I will always respect you and be your friend." The Trump assault comes at a difficult time for Leona Helmsley, who is preparing for a June trial on charges of tax evasion and fraud involving millions of dollars in renovations to the couple's 26-acre estate in Greenwich, Conn. A federal judge ruled earlier this month that Harry Helmsley, 80, probably will be unable to stand trial with his wife because of poor health and a failing memory. The letter to Leona (more juicy excerpts in a moment) stems from (surprise) a financial dispute. To wit, casino magnate and multibillionaire developer Trump recently purchased a chunk of Atlantic City real estate from Penthouse International Ltd. for $56 million, and plans to convert an unfinished casino into a noncasino hotel. Included in the property is a small parcel owned by the Helmsleys that had been leased to Penthouse for 100 years. Trump charges that Leona Helmsley has refused to transfer the lease to him, in what should be a routine transaction, out of sheer animosity. "I'm taking her to court," Trump said in a telephone interview today from Atlantic City. "In the real estate business you don't do that ... The woman is a total disgrace to the industry and humanity. This is a bad woman." Helmsley's office at the Helmsley Palace Hotel referred a reporter to her Washington lawyer, Gerald Feffer, who said he could not comment because of a gag order imposed by the judge in her criminal case. "We really have no choice but to not say a word," he said. The Trump letter voices a line of criticism that others have only whispered: that the scheming Leona has brought down her second husband, once a penny-pinching pillar of the real estate community. This is also the thesis of "Palace Coup," a recently published book on the Helmsleys by Michael Moss. "Over the last number of years," Trump wrote, "I have watched as you have virtually destroyed my friend and a once-great and respected man, Harry Helmsley. Almost no one knows Leona Helmsley better than Donald Trump, but when the press (and others) would ask about you, I would always try to speak of your few (in my opinion) normal or positive traits ... I am holding back no longer." Trump's letter depicts Leona Helmsley as a rival seething with jealousy. "When you sold me the St. Moritz Hotel and I was able to increase the gross operating profit almost five fold ... I heard you were very upset. Recently, after I sold the hotel for substantially in excess of $100 million more than I paid you, rumor was that you were beside yourself." One friend of Trump's called the letter a reflection of "a very deep hatred" that has been simmering for 15 years. "You know how sometimes you're really angry and you write a letter and never send it? He sends it!" said the friend. Another source close to Trump says Helmsley courted the young developer when he was starting out, always seating Trump next to her at dinner parties. But she grew angry when Trump won a huge tax break from New York City for his Grand Hyatt Hotel on 42nd Street, not far from the New York Helmsley, and refused to speak to Trump for several years, the source said. "The funny thing is, she always kisses my {backside} when she sees me," Trump said. Trump hasn't had a really good feud in months, at least not since he buried the hatchet with New York Mayor Edward Koch -- whom he had previously called a "jerk," a "loser" and an "idiot" -- in a New Year's Eve meeting. Besides, Trump seems to enjoy writing nasty letters. Several of them are published in the May issue of Spy magazine, which features a stupendously unflattering, zoom lens cover photo of Ivana Trump's face. "I hear through the grapevine that you are doing an extremely inaccurate and dishonest story on Ivana," Trump wrote to Spy in February as part of a continuing correspondence in which he threatened "major litigation" over the piece. "What could be more thrillingly romantic," the satiric article asks, "than to be married to a man who insists that everything he has -- even YOU -- is better, bigger, faster, longer, shinier, newer, prettier, taller and just plain more expensive than anything anyone else has?" Trump said he hasn't read the piece. "A garbage magazine," The Donald huffed.