MEMO TO: Sr. Jorge Luiz Calife of Rio de Janeiro RE: Advisability of sequel to ''2001: A Space Odyssey.'' According to a note at the end of Arthur C. Clarke's new novel, you are partly responsible for persuading the author that a sequel to ''2001'' would be a good idea, long after Mr. Clarke had concluded that such a sequel would be ''clearly impossible.'' I don't know exactly what you said to him in your letter, Sr. Calife, but I wish you hadn't.

Clarke deftly blends discovery, philosophy and a newly acquired sense of play that manifests itself in references to films like Alien and Star Wars, and snippets from recent headlines. If, by the end, he leaves readers as bewildered as his astronauts, they can at least claim to have been better entertained.