Is this the way it really is inside those hallowed halls? -- say it isn't so. But Carter, alas, has been there as Director of Publications for the Museum of Modern Art, and we dimly remember some headlines. . . . His hero, Lloyd Thatcher, the ""wunderkind of the west,"" has been imported to lead a major New York institution -- but in which direction? The artists have turned rascally and radical, demanding free access, ethnic wings, etc.; the Directors have a 60 million dollar building project in mind and want to court rich patrons for the money; the museum itself is running $100,000 in the red; while scout-hearted Thatcher merely wants to make this ""the most exciting Museum in all the world."" The excitement comes with his mishaps, as when an old artist friend mutilates a painting in protest; or when the prints he has lent, against advice, to a shoestring Harlem exhibit get soaked by burst waterpipes; or when the filmmakers at the fountain decide to do a nude scene; or when his pet venture, an experimental environments exhibit, becomes too much like the environment outside. None of this is funny, and for Thatcher things are not much better at home (but how could they be since he's never there?), but then the pretty pictures are all on the other side and this peek behind depends on a special interest.