Calvin Trillin is retiring his "U.S. Journal" column in The New Yorker, effective this fall. For 15 years he has chronicled the PTA meetings of the nation, investigated alcoholism among Indians, conversed with Rotarians, while slipping in as much writing about food as he could get away with.

The cessation of "U.S. Journal" does not appear to be the end of an era. The era will continue on, and so will Trillin, who writes books, a humor column for The Nation, is a co-host of a discussion group on cable TV and frequently appears as a defender of Kansas City, his home town, on "The Tonight Show Starring Johnny Carson."

"But I was beginning to hear an echo on some of the stories," Trillin said yesterday from a room at the Arizona Inn in Tucson, the venue of his current assignment. "I thought I should explore some other options. For example, insurance sales. Or I thought about opening a small hardware store, with an apartment upstairs." A third alternative was staying on at The New Yorker, "which I decided to do."

"When I first started writing about topics outside of New York, my friends thought it was 'quaint,' " he said. "But in recent years newspapers started to do it, too. Frankly, this was very irritating to me. I thought everybody had agreed it was my beat. So I'm just taking my bat and ball and walking away."

He is not sure what he will write for The New Yorker this fall, after returning from his traditional summer-long sojourn.

"I would like to write some things that take advantage of what I have learned. Stuff that has stuck in my head, so to speak. What editors call 'thumbsuckers' but writers call 'think pieces.' " He reflected a moment. "Actually, it's probably beyond me," he added.

The New Yorker, a prestigious weekly magazine, specializes in book-length articles, some of which take all week to read. But Trillin says he tends to stop writing at the moderate length of 3,000 words. "Not, as some people say, in the middle of a sentence, however."

He has speculated to his wife, Alice, that he may in fact "have reached a new maturity." This he bases not so much on breaking away from "U.S. Journal," but on a recent trip to Santa Fe during which he did not obtain any green corn tamales from Mrs. Rivera.

However, it was pretty clear even on the phone from Tucson that Trillin had machaca very much on his mind. "Oh my god, it's excellent here," he said. Machaca, he explained, is "a Mexican dish with a cross-cultural relationship to moo shu pork."

Food comes to Trillin's mind often, but it first came to his "U.S. Journal" as a sort of comic relief from the tales of murder and other serious issues discussed there. He wrote about pizza, about catfish, and he gave a measure of fame to Arthur Bryant, who runs a rib house in Kansas City. He wrote a lot about Kansas City, which he claims aspires to cosmopolitanism, but maintains a sign at the city limits inscribed, "Psychiatrists: Don't Let the Sun Set on Your A-- Here."

"Somebody just called me and said that Arthur is 80 now, and what should they do for him. I suggested renaming the airport 'Arthur Bryant Airport.' It would have a nice ring to it. I always thought 'Kansas City International Airport' was a bit fanciful, anyhow."

His schedule for those 15 years was that he would spend about a week on the road, a week writing and a week looking for his next topic. During the topic week, he also wrote a column for The Nation for which he was paid "in the high two figures."

He'll continue that. "Actually, I get a straight century $100 for those," he said. "I held out for the century, because when editor Victor Navasky offered the 'high two figures,' it turned out he really meant $65."

Trillin denies that he is giving up "U.S. Journal" because of the rigors of travel, or that, in the parlance of working reporters, "his legs are gone."

"No," he said, "I'm going to miss starting off on Monday mornings with the traveling salesmen and the regional auditors and everyone else. Of course, they had clothing bags. Apparently they thought they should change suits."

He will miss researching the effect on Boulder, Colo., of a minister who reveals that he is a homosexual. And he will miss touring Reading, Pa., with the authors of "The Beer-Drinker's Guide to the Bars of Reading." "They dedicated that book to their wives, you know," Trillin said admiringly.

What he learned from 15 years of "U.S. Journal" is quite easy to sum up, he says:

"A law should be passed that any city which fails to clearly mark the route to the airport shall lose one major league franchise. This is not a deep thought, I know. But it is practical legislation."