WE WERE BOTH saddened and outraged by the announcement of ventriloquist Edgar Bergen that after 56 years, he and his dummies, Charlie McCarthy and Mortimer Snerd, are going into retirement. Mr. Bergen will be making his final appearances in the next few weeks at Caesar's Palace in Las Vegas, and odd, glittery place for a man who made his fortune in the comparatively staid medium of radio. Of course, that was even odder, since the idea of doing ventriloquism on radio, much less fo succeeding with it, was something that could only occur in the 1930s. On May 9, 1937, "The Chase & Sanborn Hour" began, and within a year had overtaken "The Jack Benny Program," "The Eddie Cantor Show" and "The Kraft Music Hall." It lasted until Dec. 26, 1948.

One reason for Mr. Bergen's success on radio was that he wasn't really a top-flight ventriloquist; he moved his lips, as Charlie continues to remind him. But he was - is - a brilliant comedian, at least part of whose brilliance was due to the impression of a high, rather dignified intelligence, which he conveyed in movies as well as on the air. One of his movies, "You Can't Cheat and Honest Man," co-starred W. C. Fields, who sustained a running feud with Charlie McCarthy on the radio show. Mr. Field would threaten to carve Charlie into a venetian blind, and Charlie would reply: "That makes me shudder."

Well, it's curtains now, which accounts for our saddness, but not for our sense of social outrage. That proceeds from the fact that the Smithsonian Institution, which seems to be specializing in furniture lately, having just last week made room for Arhie Bunker's chair, is evidently about to take in Charlie McCarthy, while leaving Mortimer Snerd up a tree. One quick look at the two dummies will tell you why: Charlie McCarthy, in his monocle, top hat, white tie and tails (he also has a fancy cowboy getup, a Foreign Legion outift and a Sherlock Holmes detective suit), is confident, brash, pampered; Mortimer Snerd the bumpkin in an ill-fitting, high stiff collar and straw hat, is buck-toothed, huge-eared, red-faced. Charlie was made master sergeant in the Army Air Corps and was awarded a Master of Innuendo from Northwestern. Naturally, he was the favored son, though he always addressed his benefactor as "Bergen" in contrast with Mortimer's "Mr. Bergen." Even now, Charlie has the nerve to remark, "I think the Smithsonian was exercising good taste."

We think not. In fact, had we to choose between the flashy Charlie McCarthy and the down-to-earth Mortimer Snerd, we'd take the bumpkin in a minute. True, Charlie could put down Mr. Fields, but Mortimer could, and did, put down Charlie. Is this why Mortimerr is being excluded now, as punishment? Or is his exclusion merely part of a pervasive national anti-rural bias, which simply will not abide a fellow who expresses himself with "a-yulh, a-yulh, a-yulh"?

Of course, the other, and comforting, way to look at this decision is that while Charlie McCarthy becomes a public exhibition, enshrined but alone, Mortimer Snerd may stay home with Edgar Bergen - there to sit up nights and chat.