LAST year at this time, grad student and part-time liquor store clerk Jay McInerney had not yet met Mick Jagger. Nor had Maryland insurance agent Tom Clancy dined at the White House. And, up in Maine, Carolyn Chute's mother had no reason to display on her car a bumper sticker warning that state's most famous writer: "Move over, Stephen King!"

However, since then, the debuts of these three first novelists -- Bright Lights, Big City (McInerney), The Hunt for Red October (Clancy), The Beans of Egypt, Maine (Chute) -- have made them household words in those households where new books loom large. What are the effects of sudden fame and fortune? Is it all tax shelters and dinner parties with George Plimpton, or does th kitty litter still need to be sifted? Bright Lights, Bright Lad

MY LIFE has sort of turned around," comments McInerney with an expressive, definitely appreciative chuckle. After all: "Getting flown first-class to Hollywood for the first time is rather head-turning when you've just been working in a liquor store and fending off the landlord."

Bright Lights, Big City, published by Vintage as an original trade paperback last September, is now up to 125,000 copies in print, with sales still brisk. And, in a rather uncommon switch, various publishing houses have been making (so far unsuccessful) bids to produce a separate mass-market edition. McInerney, meanwhile, has been working on the BL, BC screenplay (heartthrob Tom Cruise is set to star), having given up both his doctoral program at Syracuse University and his job sliding half-pints into paper bags. "All my life I've wanted to be a writer," the 29-year-old declares, "and I'm now happily" -- he pauses -- "unaffiliated."

Better still, no "second novel blues" are afflicting him; that book's already completed and due out in September. And McInerney says he's grateful he'd finished "a really important draft" of Ransom, as it's called, before BC, BL "took over." In fact, number two might have been number one, had his muse not turned fickle. While working on the manuscript that became Ransom (which is set in Japan, where he lived for two years), McInerney found himself "sneaking away, going to a different typewriter and starting unfaithfully to write Bright Lights." The Hunt for Business as Usual

TOM CLANCY, unlike Jay McInerney, hasn't given up what he was doing, pre-best-sellerdom, in order to follow the novelist's trade. "I'd like more time to write," he confesses, when asked if he's switched his focus from selling insurance. "But it's a family business; there are 1,100 clients -- a lot of them friends -- and I'm not going to desert them."

With no little amusement, he points out that turning into a talked-about, sought-after blockbuster author after a career as an insurance agent is like "being cured of leprosy -- before, when you told them who you were and what you did, people avoided you like the plague." Now, the press calls regularly -- even, Clancy notes with some disgust, to ask him his opinion about the Walker naval spy ring case. "I tell them all I know is what I read in the papers!" (This, remember, is the man who created a highly detailed submarine chase story without ever having set foot on a submarine.)

There are 235,000 copies of the Naval Institute Press edition of Red October in print; the foreign rights are already nailed down in 10 countries. A new novel ("a naval subject, somewhat more ambitious") is in the works, promised to Putnam for delivery in early'86, with publication in the fall of that year. But what are the special high points, since Clancy and Red October were launched early last autumn? "I've talked to the president, lunched at the Pentagon, been in an airplane four times and met Prince Andrew." He's also building a new house. "Meeting the people has been the nicest part," Clancy said. "People are nice, if you give them half a chance, including Washington big shots." The Beans of Maine Talk Back

CAROLYN CHUTE didn't have a telephone last year, partly owing to economics and partly because she felt it interfered with the quality of her life. With the nearly meteoric success of her novel, The Beans of Egypt, Maine, however, she had one installed, then got an answering machine. Now the phone's there, but unplugged, and Ticknor & Fields, her publisher, must send mailgrams to get her attention. Says Gwen North Reiss, T & F's publicity director, "She wrote us that there's 'no such thing as a wrong letter . . . at two in the morning.'"

"Her daily life hasn't changed much," Reiss adds, "except she's bought a piece of land about an hour away from her current house, and she's going to build a place to live where barking dogs won't keep her from writing." In January of this year, Chute's novel was published simultaneously in hardcover and trade paper; the two, combined, make a total of 235,000 copies in print.

A phemomenon in her home state, where Stephen King reigns as best-selling native son, Chute's novel continues to sell there in enormous quantities. From Bookland of Portland, Maine, a wholesaler and 11-store chain, book department manager Kathy Judkin reports, "We've sold 12,000 and it's still going out the door."

Yet some folks Down East are buying The Beans of Egypt, Maine just to see if it fulfills their worst suspicions, and Chute has now received in the mail copies with the cover ripped off. Anyone named Bean is particularly incensed at the novel's portrayal of a dim, rowdy, incestuous clan who they feel does not in the slightest resemble themselves.

A front-page headline in the Portland Press Herald bannered, "BEANS OF MAINE AREN'T FLATTERED" and quoted an irate Chester H. Bean, 86-year-old patriarch, saying, "I never knew a Bean like that." His family was "respectful" and went to church on Sunday, he went on, even though they had "plenty of patches on their pants." But, for better or for worse, Carolyn Chute and the Beans are tied together now in literary immortality. And even though the real ones would be horrified to hear, a passer-by came up to Chute in an airport recently, gushing, "Aren't you the famous writer, Carol Bean?"