All these crimes provoke a disturbing thought: why were so many honorable men working for such a blatantly corrupt organization? Either they were duped; or then again, perhaps their cooperation was prompted by something else. Could Nugan Hand, though a private organization, have functioned as a bank for covert C.I.A. operations?

Dutifully, Mr. Kwitny quotes the C.I.A.'s assertion that it ''had no ties with the Nugan Hand Bank.'' Yet this denial, he feels, can only lead to a disturbing conclusion. He quotes an Australian official who investigated the bank: ''What you're left with is saying, here are all these patriots who have served their country faithfully for years, suddenly saying, 'Let's all become criminals. Let's forget our war service, our heroism, and go out and commit crimes against the very country we've been working for.' ''

Mr. Kwitny, however, offers no firm resolution to this fools-or-knaves riddle. Again like the Iran-contra hearings, there are no smoking guns, only a scatter shot of fascinating speculations. Mr. Kwitny's search for truth becomes a search for hypotheses. In the end, he offers not proofs but theories. And that is part of the book's strength.

''The Crimes of Patriots'' is a model of responsible investigative journalism because it avoids claiming to be more than it is. It is not, Mr. Kwitny announces in the beginning, ''a book for people who must have their mysteries solved.'' And, true to his word, there is, in fact, a list of 57 ''questions whose answers are secret'' in an appendix. Yet, these mysteries only help to reinforce one's admiration for Mr. Kwitny's reporting and the clues he uncovered. The unanswered questions - and their implications about the conduct of this country's foreign policy - are as resonant as the ones he does answer.

THERE is also a curious afterword to the book. A publisher's note explains that Admiral Yates, who refused for five years to be interviewed by Mr. Kwitny, was asked to write an unedited and unaltered rebuttal. He agreed, and he is given, in effect, his own day on the stand. He's no salesman like Oliver North.

The admiral, calling the group of former military and intelligence officers he helped attract to Nugan Hand ''The True Patriots,'' explains that when he first joined the bank as its president he ''undertook an intensive self-taught accounting and business-law course.'' And, equally commendable he apparently feels, he was enrolled in the Harvard Business School when the bank collapsed in 1980. One wonders, though, if the admiral would be so enthusiastic if the Navy had a policy that allowed him to become the commander of an aircraft carrier (which he had been) before he had ever learned to sail a sunfish.

The admiral also asserts that ''The True Patriots served honestly and loyally the interests of Nugan Hand and its clients. They had grown up in the military service and spent their lives in the company of gentlemen well known for honesty and honor, where it is commonplace to risk one's life, not just one's money and reputation, based on the word of a colleague.''

Fine sentiments. And again one is reminded of a moment during the Iran-contra hearings. Having listened to Colonel North's recitation of his patriotic motives and praised the sincerity of his testimony, Representative Dante B. Fascell, the vice chairman of the House Select Committee, turned to the witness and said, ''But I keep asking myself, 'How come I don't feel good?' '' It is in the contemplation of an answer to that despairing question that one appreciates the significance of ''The Crimes of Patriots.''