A document dismissing the charges was filed by the United States Attorney, Rudolph W. Giuliani, in Federal District Court in Manhattan. He conceded that the prosecution could not prove that the defendants did not believe that their planned weapons sales were ''officially sanctioned.''

All the defendants were free while awaiting trial. In addition to Mr. Evans, the defendants were Avraham Bar-Am, the retired Israeli general; Guriel Eisenberg, Rafael Israel Eisenberg, William Northrop, Nico Minardos, Alfred Flearmoy, Hermann Moll, Ralph Kopka, Hans Bihn and Isaac Hebroni. Lawyers said Guriel Eisenberg had died.

In the dismissal document, the prosecution noted that the indictment was filed May 5, 1986, adding that the grand jury heard ''substantial evidence'' to show that the defendants had conspired to divert American-made weapons to Iran.

''In November 1986, the fact that certain members of the National Security Council had secretly engaged in the sale of arms to Iran was disclosed publicly for the first time,'' it said. Key U.S. Witness Dies

The prosecutors investigated whether there was ''any connection between the Iran-contra affair and the arms transactions charged in this indictment,'' according to the dismissal document. It said, ''This investigation revealed no such connection.''