John Updike seems to be trying to have things at least three ways in this sequel to ''Bech: A Book'' (1970).
First there is a tip of the hat to fictional author Bech's former editor, fussy about vulgar prose, who is now gone, ''taking his decent, double-breasted era with him.''
Then there is Bech's own sensitivity when he sees ''lightly toasted teen-agers'' on the beach actually reading his raunchy new best seller, a Book-of-the-Month Club ''Alternate Alternate'' selection with a Special Warning to Squeamish Subscribers. (He wanted to ''pluck the book from its readers' hands'' and explain that it was ''unworthy of their time let alone their money.'')
Then there are the sexual adventures and four-letter words exploited by nonfictional author Updike himself, who evidently had no equivalent of Bech's decent editor at hand.
To give it the benefit of the doubt, this is all part of the satire in the main segment of ''Bech Is Back,'' a BOMC Alternate with no special warning to anyone. And Updike can be tellingly funny about a literary age when Bech's once-patrician publishing firm has been sold to a supermarket chain that peddled it to an oil company that managed to foist it off on a West Coast lumber-and-shale-based conglomerate. Interwoven with this theme are the marriage and removal to the suburbs of the highly urbanized Bech: ''There was no ignoring the noise in these environs. . . . The ringing phone was never in someone else's apartment, and the child crying downstairs was always one's own.''
Among prime Updikean moments in other sections of the book are some with Bech on the inane talk-show circuit. The skill remains when Bech visits the third world, but the tone is ambiguous - somewhere between the required empathy and the condescending wit of Evelyn Waugh abroad.
Such wit is more called for in the hollow artsy Manhattan party that concludes the volume. One guest says he wished Bech's novel were even dirtier. It is Bech's saving grace that, for all his own flaws, he is ''not quite satisfied'' with scenes like this.