Francis G. Doherty, a Boston attorney representing David Beck of the A.F.L International Teamsters Union, has offered local book sellers more "advice" against selling "U.S.A. Confidential."

In a letter received by Square merchants yesterday, Doherty advises that his office will sue, on Beck's behalf, "any person firm, or corporation, who sells, delivers, or circulates this book."

The letter, dated March 11, says the Jack Lait and Lee Mortimer book contains "defamatory statements concerning Mr. David Beck of Seattle, Washington, which tend to expose him to hatred, contempt, and ridicule... Mr. Dave Beck intends to sue the authors and publishers of this book."

The action is similar to that taken by State police last week, when they advised all booksellers that sale of "U.S.A. Confidential" might lead to court action for libel.

However, in a statement Thursday, the Massachusetts Civil Liberties Union "questioned" such unofficial tactics, and suggested legal action be taken against the book itself.