THE BEST BOOK BARGAIN in the country these days can be found in an unlikely spot: McDonald's. That's because Western Publishing, home of Little Golden Books, is celebrating this line's 40th anniversary and for the next five weeks will see five of their Little Golden titles featured, one a week, in Fast Foodland. MaryAnn Buege, McDonald's account coordinator at Western, told "Book Report" that it's a "brand-new approach for McDonald's" who last year distributed 13 million of the Western-designed-and-printed Ronald McDonald Coloring Calendars. That may sound like a drop in the bucket compared to the 40 billion burgers the signs currently proclaim, but no publisher could do anything but gulp in the face of such a figure.

Anyway, the Little Golden Books--The Monster at the End of this Book (a Sesame Street title), The Pokey Little Puppy, Tom and Jerry's Party, Benjie and Country Mouse, City Mouse--are officially part of the Little Golden Book "Happy Meal" Promotion. Every time a kid orders a "Happy Meal" (regular hamburger or cheeseburger, small fries and a drink), he gets the book of that week. Plus, since there may be, as Buege says, "grandparents who want the books but not that menu" the book of the week can also be purchased for 29 or 39 cents. The exact price may vary from one franchise to another, but, however you look at it, it's a great deal. Ordinarily the books retail for 89 cents.

This promotion to encourage reading has been in the works at McDonald's and at Western for over a year. But who knows what the other speedy eateries might have up their conglomerate sleeves? Maybe Roy Rogers could stock the novels of Zane Grey or Louis L'Amour, or, better still, maybe Arthur Treacher's should offer British mysteries. After all, the late Mr. T was best known for his portrayal of superior servants. So, who buried the fish sticks in the breading? Why, of course, the butler did it.