COLONEL Z is the life of Sir Claude Dansey, vice chief of Britain's Secret Intelligence Service (also known as SIS or MI6) during the Second World War and the first biography of a head or deputy head of that service since its creation early in this century. That it was authored by British writers and first published in the United Kingdom shows how much things have changed from days not too distant when the identity of even the chief of that service was always a secret and he was only referred to as "C."

Why Dansey for this first? Secretive, irascible, manipulative, influential and highly controversial, he is the stuff of which legends are made. Cameo shots of him in previous works have whetted the appetite for a fuller picture. For authors Anthony Read and David Fisher, a biography is a natural extension of their 1980 book, Operation Lucy, about the Soviet spy network in Switzerland in which they claim Dansey played a central and controlling role.

Aside from information on the very early years, the authors have brought together some new, scattered or forgotten facts on Dansey. Among these are his advisory role to the fledgling U.S. Army intelligence service in World War I and its "father," General R.H. Van Deman. We learn of some of his counterintelligence work with the security service MO5 (later MI5) and are reminded of the exploits of such Resistance heroines as the marvelous Marie-Madeleine Fourcade. The authors perform a needed service by questioning certain stories about Dansey spread by the Soviet agent and defector, Kim Philby, which, unchallenged, have became part of conventional wisdom. But, sad to relate, there are numerous flaws adding up to some tenuous intelligence history. Try as they might, the authors fail to convince that Dansey was as good and successful as they believe.

One of the most serious errors -- which raises questions of reliability -- is their perpetuation of the story that the Lucy net was controlled by Dansey and used to disguise the Ultra origin of the information the net was passing to Moscow during World War II. Read and Fisher not only fail to deal with the many criticisms of their thesis (and earlier versions of it by others) but, more significantly, do not explain their tenacious advocacy in the face of its authoritative rejection in F.H. Hinsley's official history of British intelligence. An incomprehensible omission is their failure to discuss Dansey's performance as chief in Rome during the Ethiopian crisis of the 1930s. By some accounts SIS as a whole failed to distinguish itself at that time. What SIS Rome, in the center of great events, did or did not do is of infinitely greater importance than many other matters discussed.

The lack of citations for particularly controversial matters is especially disconcerting. We are expected to accept on faith that Dansey's prewar organization, "Z" (hence the title), was a success when contrary opinions, which they do not address, exist. There is no way of knowing if they have harder evidence for their story of the supposed indirect links of the Abwehr's Admiral Canaris with SIS than that produced by other writers. Inferentially presenting the Gaullist agent R,emy's accomplishments as a Dansey success might be seen as an attempt to appropriate them. All this just won't do.

IN CONTRAST, Anthony Master's subject, Maxwell Knight, is not as major a figure in intelligence annals but an interesting, shadowy one nevertheless. A senior case officer, he ran a special countersubversion unit of MI5 until 1946. The title proves that he too had the stuff of which fictional characters are made (though Masters clarifies that Ian Fleming's famous M in the James Bond series was an amalgam).

Knight does not fit the popular impression of the conventional career security type. A naturalist, imaginative and eccentric, he was by this and other accounts, homosexual. His unit was separated functionally from MI5, raising interesting questions of precise headquarters control. Of his operational work recounted, four cases are of particular historical interest. Master's treatment of the Tyler Kent case (involving a U.S. code clerk at the London embassy in 1940) is one of the most extensive yet printed and contains material which has not appeared before. Other accomplishments like the Woolwich Arsenal spy case uncovered are balanced with the failures and examples of amateurishness. The personal side of the complicated man comes across much better than the largely one-dimensional portrait of Dansey.

Fortunately, Masters is better at citing sources. Still, there are lapses such as the flight of Nazi leader Rudolph Hess being attributed to a British intelligence operation. Read and Fisher speculate but make no such claim. The chapter on Knight's efforts to alert his superiors, including Churchill, to Soviet penetration of the security services would have been strengthened by some attributions. Virtually nothing is said of the communist spies at Cambridge (Philby et al.) and whether Knight shared in security's failure to thwart them. All the same, this is a rare- angle look into a portion of the misty world of counterintelligence and countersubversion and the story of a personal life equal in interest to the professional.