Churchill during the 'lean years,' new Masterpiece Theater mini-series

''I have often eaten my words, but in the main have found them a most wholesome diet,'' says Robert Hardy in his role as Winston Churchill during the lean years of 1929-39.

Those lines symbolize the unique mixture of arrogance and humility of the man , the best and the worst of not only the career of Churchill, but the new eight-part Masterpiece Theater series Churchill: The Wilderness Years (PBS, starting Sunday, Jan. 16, 9-10 p.m., check local listings)m .

The mini-series spans Churchill's years from his loss of office (and fortune) in 1929 to his triumphantly somber return to the political spotlight in 1939 at the outbreak of the WWII he had been predicting all along, with all the ups and downs in between. When it is good, it is very very good; when it is bad, it is just a little boring.

Adapted by John Prebbel and William Humble for England's Southern Pictures from Martin Gilbert's authorized biography, directed by Ferdinand Fairfax, and written by several different scripters, ''Churchill'' is filled with the trivia as well as the backbone of English politics as seen through the eyes of the great man who laid bricks for relaxation. Churchill's relationship with his wife and his children, as well as his love for his homes at Chartwell Manor and Blenheim Palace (both of which are used as locations), plays an important part in the mini-series.

Sometimes, however, there is just a bit more about the intricacies of the British parliamentary system than an American audience might care to know. But Anglophiles will find every moment of it fascinating.

Fascinating to everybody, however, is bound to be the superb portrait of Churchill painted by Hardy (the vet in ''All Creatures Great and Small''). Using familiar gestures, attitudes, and stances, Mr. Hardy manages to get at the essence of the man without turning the performance into a mere facile impersonation.

Together with Sian Phillips (Livia of ''I, Claudius''), who gives a bold and liberated performance as Churchill's beloved wife Clemmie, Hardy delves into the poignant nuances in the character of this complex statesman. The series examines , sometimes in minute detail, the motivation of this man, who so often suffered personal and military defeat as well as political humiliation before in his later years he became a major force in Great Britain's - and the world's - heroic stand against Hitler.

''The Wilderness Years'' makes valuable contributions to the backstairs perspective of history in detailing the private life of Churchill as well as recording for traditional historians the agonizing years that witnessed the dissolution of much of the British Empire as well as the triumphant victory in WWII. Together with the recent mini-series on ''Jennie,'' television audiences have now been provided with an unprecedentedly wide-ranging multilevel biography of a great man and what made him so great. Now, there are just the war years to go. Televising the 'Ring'

Now that the promotional hoopla for ''Nicholas Nickleby'' has died down, television audiences are being subjected to the same kind of high-quality promotion in advance of the unprecedented ''Great Performances'' presentation of Wagner's ''The Ring of the Nibelung.'' It is the first time the complete cycle has ever been aired on television.

The hype really gets going next week. A Ring for Television (PBS, Monday, January 17, 9-10 p.m., check local listings)m is being aired as a Great Performances special.

Call it hype or hoopla, but the fact is that this documentary is a fascinating introduction not only to the Bayreuth Festival, where the series was shot, but an entertainingly informative study of Richard Wagner's works and their place in our society.

Enfant terriblem director Patrice Chereau, conductor Pierre Boulez, and TV director Brian Large take part in the film, as does Wagner's granddaughter Friedelind, who acts as a sort of tour guide. Major performers also appear on camera both in their singing roles and in candid interviews.

Chereau's avant-garde production uses costumes and attitudes of the l840-1920 period, focusing on the ''Ring'' as an allegory for the breakdown in society caused by the Industrial Revolution. Wagner, according to this interpretation, used mythology to tell the story of his time.

''A Ring for Television'' will have you hungering to see and hear the ''Ring'' itself. Well, the 17-hour series premieres with ''Das Reingold'' on Monday, Jan. 24, on PBS (with stereo simulcasting in many cities), and continues intermittently during succeeding weeks.