Tale of two brothers - a good read; Green Desire, by Anton Myrer. New York: G.P. Putnam's Sons. 511 pp. $14.95.

This novel is a good read - as good as Myrer's best-selling ''The Last Convertible'' - but it's not as good a book. One-dimensional characters and a melodramatic ending eventually spoil the magic. You'll find characters like Chrissie and Russ and George of ''The Last Convertible'' appearing again, though , of course, with different names.

''A Green Desire'' opens in the early 1900s, with the major events of the period - World War I, stock market crash, and World War II. The story follows the lives of two brothers, who, with their mother, are abandoned by a fortune-seeking father. Aunt Serena, a rich spinster, invites the boys to live with her on Boston's Beacon Hill, promising they can attend prep school, then Harvard, with summers in Europe.

Who could resist such an offer? Not self-centered Chapin, who can't pack his bags fast enough. Younger brother Tipton longs to go too, but knows his mother can't make it alone. He stays behind and supports her.

As the boys grow up, the chasm widens until, on the brink of manhood, Chapin has become all that typifies the evil side of capitalism - a desire for greenbacks and no conscience. Tipton is the other side of the coin - the American Dream-er, a salesman who makes a go of anything he believes in. For him it's people who count.

We've all met Myrer's characters: the rich, manipulative aunt; the competitive brother who considers money the adult's report card; the boy who shoulders a man's burden; and the spirited, desirable woman. But, Myrer's biggest fault lies in painting Chapin too black, making him a cardboard cliche. In spite of faults, the story holds you captive. Its only afterward that you realize the product isn't as good as the salesman.