A single telephone call from a Du Pont public relations man to the Book-of-the-Month Club financially doomed an unflattering history of the DuPont family and its businesses, according to allegations made in a trial here yesterday.

In a case with potentially broad implications for the publishing industry, the author of the history alleges that his 1974 book was irredeemably damaged because his publisher and a book club were intimidated by Du Pont interests.

The suit, brought by Gerard Colby Zilg, names as defendants E.I. du Pont de Nemours & Co. Inc. and Prentice-Hall Inc., the publisher of his book, "Du Pont, Behind the Nylon Curtain."

Zilg's allegations of breach of contract by Prentice Hall and interference with contract relations by Du Pont hinge on a telephone call on July 25, 1974, from a Du Pont public relations executive to an editor at Book-of-the-Month Club Inc.

According to a memo produced in pretrial discovery and written by Du Pont public relations man Harold G. Brown Jr. to his superior, Brown told the Book-of-the-Month Club editor that several persons at Du Pont, including attorneys, had read a manuscript of the book and found it "scurrilous" and "actionable."

Book-of-the-Month Club had contracted with Prentice-Hall to have "Du Pont" included as a November selection of its Fortune Book Club, according to the suit. But several days after the call from Du Pont, the club informed Prentice-Hall that it would "defer" plans to issue the book. Not long after that, Prentice-Hall reduced its press run of the book from 15,000 copies to 10,000, according to the author's complaint.

Du Pont, in court papers, argues that it had a First Amendment right to voice its objections to a book that disparages the reputation of the Du Pont company.

What makes this case unusual and interesting to the publishing industry is that there is little formal law about publishers' contractual responsibilities. Authors are often discontented with this aspect of their book contracts, which industry experts claim are purposely general on the question of the extent of the affirmative obligation of publishers to promote a book and to maximize sales.

In this case, Zilg is seeking to pin down precisely what the publisher's responsibility is. At issue is whether Prentice-Hall acted in good faith and for legitimate business reasons or reacted out of fear of Du Pont's money and power and without concern for its contractual partner, the author, according to Zilg's attorney, Ronald E. DePetris.

DePetris contends that this was not simply a matter of the company publicly voicing an objection to the book. Rather, says DePetris, it was a private communication designed to interfere with an existing contract. Alleging that Prentice-Hall let "Du Pont" die because the publisher had been intimidated by the company, Zilg is seeking $350,000 in compensatory damages and $1 million in punitive damages for lost royalties, paperback licensing and overseas book sales, among other things.

Prentice-Hall, for its part, claims it fulfilled its contract to publish, promote, sell, and reprint the book, says it acted as it did strictly for business purposes and calls Zilg's claims to the contrary "utter nonsense."

One expert witness for Zilg's side said in an interview that Prentice-Hall's most serious offense was not using Du Pont's call to publicize the book. William Decker, an author and editor, said, "If I were publishing a sensational expose and somebody tried to stop me, that would be the best thing that could happen to me. I would have published it as the book that Du Pont tried to suppress. That would have been my headline."

It's not surprising that the Du Pont interests were upset by the book. From virtually the first of its 623 pages, "Du Pont" is relentlessly critical of the business and personal affairs of the famous family, which the book traces from 18th century France to its power base in Delaware.

Zilg first contracted with David McKay Co. Inc. to write the book, but after reading a portion of the text, McKay tried to pressure Zilg to take on a co-author. Zilg then switched to Prentice-Hall. The Du Pont expose was a departure for the normally conservative publisher, whose usual fare is textbooks and "how-to" books sold by mail order.

But the court records make it clear that Prentice-Hall was aware from the beginning that "Du Pont" would be controversial. For example, in a June 15, 1972, memo to his superiors, the editor assigned to the book, Bram Cavin, wrote that "Du Pont" would depict the family "torn by feuds and struggles over the money and the power."

On Dec. 11, 1973, Cavin sent the "Du Pont" manuscript to the legal department with a note describing it as "terribly long . . . and most important." Cavin added, "I don't have to tell you how much money Du Pont has. I think it requires a very careful legal reading."

About two months later, Wayne Carson of the legal department wrote a memo declaring that he thought the book would "fall under constitutional protection." But he said Du Pont "could initiate a lawsuit with the intent to harass Prentice-Hall . . . . I think management should be aware of the possibility and should make the decision to publish, or not to, taking into consideration the risk."

Prentice-Hall decided to take the risk. Nevertheless, according to Cavin's affidavit, the publisher remained nervous until April, 1974, when Book-of-the-Month Club contracted to take the book, according to the suit. This was "reassuring," Cavin said in an affidavit filed with the court, because it gave the book "respectability."

That all apparently changed on July 25, when the book club editor told the club's executive vice president, F. Harry Brown (no relation to the Du Pont Brown), about the Du Pont phone call.

Du Pont got the manuscript when a Prentice-Hall salesman, at the behest of his supervisor, dropped off a copy at the Greenwood Book Shop in Wilmington. According to the salesman's sworn statement filed with the court, he was told to make the manuscript drop, which he characterized as "a bit unorthodox," on the basis that it would inspire the store owner to publicize the book. But the owner, who had acquired the shop from a Du Pont family member, gave the manuscript to Brice Bredin, son-in-law of Irenee du Pont Jr., who passed it along to the company public relations department, according to court papers.

When Book-of-the-Month Club's Brown read the book, he decided he didn't like its "tone," and decided to "defer" offering the book to subscribers of the Fortune Book Club, according to depositions filed with the court. Brown called Peter Grenquist, president of Prentice-Hall's trade book division, telling him he was having second thoughts about the book.

After Prentice-Hall was informed of the book club's decision to defer, the publisher made no effort to enforce its contract with Book-of-the-Month Club or to seek money damages, according to court papers.

According to Cavin, he tried to get Prentice-Hall to publicize Du Pont's action as a way to promote the book. But Grenquist demurred, and ordered Cavin and others not to discuss the matter with the author, Zilg. In fact, Zilg did not learn of Du Pont's July 25 phone call until sometime in October, when Cavin ignored his boss and told the author, according to Cavin's statement.

Cavin testified in a deposition that he also went to The New York Times with the story, and in January the newspaper published an account of the Du Pont phone call. The Times was aided by Prentice-Hall's general counsel, William J. Daly, who secretly turned over his file to the reporter.

Court papers also show that Daly protested vigorously to Du Pont. One internal Du Pont memo quotes Daly as telling the company's general counsel that "Du Pont" was "a grand book . . . the best thing since Ida Tarbel took on Standard Oil."

Daly, who was an in-house lawyer for Prentice Hall, died before his employer learned that he was a source of leaks to the press, and Cavin, the editor, was fired by Prentice-Hall for being "unproductive."

Even as Prentice-Hall was cutting the "Du Pont" press run by one-third, the book was getting favorable reviews in major publications. The Los Angeles Times, for example, called it "a vastly readable book and. . . a very important one."

As a result of articles about the controversy, the book did become a best seller in Delaware. But Prentice-Hall chose not to give the affair national exposure, and in fact, slashed its advertising budget for the book even in the face of laudatory reviews, the author contends in his suit.