Just under its placid surface, Manchester is seething with excitement over Samantha Smith.

Just under the excitement, Manchester is as calm as ever.

Samantha, you recall, is the 11-year-old girl who wrote a letter to Soviet leader Yuri Andropov asking why the world can't have peace. Andropov invited her and her parents to the Soviet Union for two weeks, and they are scheduled to return tonight after a stop in Toronto.

Quite a delegation was getting ready to meet the plane at Augusta Airport, four miles east of this crossroads hamlet. At home, where Samantha's grandmother and a 17-year-old girl cousin have been holding the fort, a small neighborhood party is planned. Tyler Jones, the cousin from North Carolina, spent all Tuesday making a huge "Welcome Home" banner with magic marker and 10 yards of paper.

On Saturday, Manchester holds its annual Old Time Circus Day Festival with a parade, road race, baked bean supper, street dancing and Beano, the local Bingo. Samantha will lead the parade. Bob Verrill, president of the Lions Club and the local Pepperidge Farm breadman, has promised to round up a convertible.

Meanwhile, the press is back. There had been a lull after the original exchange of letters last April, and until this week, the calls to the Smith house were down to three or four a day. But by Wednesday the phone was ringing every 10 minutes.

"I don't know how Arthur did it," says Theresa Smith, Samantha's widowed grandmother, who lives in Florida but has been here helping to cope for nearly a month now. Arthur Smith, Samantha's father, somehow kept everybody happy as he juggled for weeks on end the phone, the reporters at the door, the TV people on the lawn. He finally got a public relations friend to field calls.

Right now, NBC is on the phone. What time is the plane coming in? What airline? What's the flight number? Are there reporters in the house?

Patiently, calmly, Theresa Smith repeats the information that surely NBC could have looked up for itself, and asks if they would like to interview the reporter standing next to her. They decline.

NBC hangs up and now it's ABC asking exactly the same questions. Next, the Boston Herald American. Downtown, The Philadelphia Inquirer is talking to local citizens. The reporter will be at the front door in a few minutes.

Neatly filed on a table in the study are hundreds of letters: well-wishers, appeals, notables, pen pals. A handful are negative, scolding Samantha for wearing a communist uniform (though she spurned the red scarf that goes with it because, her mother said, it "is a symbol of devotion to the Communist Party"), for writing in the first place and so on. Her days recently were filled with official visits to Soviet sights, and she laid a wreath at Lenin's tomb. Highlights of her trip included a four-day stay at an elite Communist Party youth camp in the Crimea; a meeting with Valentina Tereshkova, who 20 years ago became the first woman in space, and a trip to the Kirov Ballet in Leningrad, where she was given a pair of signed toe shoes by the prima ballerina, Alla Sizova.

"She's aware of the propaganda thing," says her cousin. "She knew about that even before she left. She's a smart kid. And none of this has gone to her head. She told me she realized it was all entirely luck, her being singled out like this."

One thing that's changed is that Samantha is no longer called "Dogface," her old nickname at school.

An only child, Samantha--who by the way is extremely pretty; her family is baffled by that nickname--has always been comfortable with adults, her grandmother says, and especially the quick-thinking, alert kinds of people her parents know. "I think it's good for the Russians to see a normal, average American family."

Her father teaches English at the University of Maine. For 10 years he taught at the now-defunct Ricker College at Holton. He is from West Virginia and his wife, Jane, is a Virginian. They have lived in Maine about 13 years.

On the walls of the modest white clapboard house, set in woods three miles from town, are hunting prints, a church rubbing, an Abbey Theater poster, art photographs, and of course the Andropov letter and a resolution of congratulations by the state legislature. One wall of the kitchen is virtually papered with newspaper clippings, some in Russian.

"Sam wants to be a veterinarian," her grandmother says. The family has two cats and a Chesapeake Bay retriever named Kim, which honors each visitor with one fierce, competent bark and then retires.

In downtown Manchester at Daggett's Market, Lloyd Smith, no relation, mans the cash register.

"If we don't see Samantha on the front page of the Kennebec Journal we think something's wrong," he says. "Couple weeks ago they had her on page two and everyone said, 'What happened?' but it's a golden thing for this kid. Wonderful it happened to someone in our community. It's too bad she's being shown just what they want to show her. She's not getting a real look at what communism really is."

He displays autographs of some Soviet newsmen who interviewed him in the store. The readerboard out front says, "Welc Home Samantha."

The market is the heart and soul of Manchester. It's where you go, that's all. The windows are plastered with notices. Besides, as co-owner Muriel Smith observes, "We're the only place around that puts mushrooms in our sandwiches."

The day's Kennebec Journal has two letters on Samantha, clearly the latest in a long series. One replies sharply to a woman for suggesting that Samantha "stay home and play with dolls, rather than promote peace." The other calls for an end to the envious sniping that has been going on.

Heidi Rogers, who came here for the summer from San Diego to help her father run Peterson's ice cream store, pancake house and bakery across the intersection, feels it was all "great exposure for Manchester and Maine. They're such a nice family, all of them. Samantha comes in here to get ice cream. I know there's some negative publicity, like the whole trip being paid for by the Russians, but it's a good thing for us and a great experience for her."

John Daggett, who owned Daggett's Market for 32 years before he sold it and who still lives across the street from it, is in the state legislature and is first selectman of Manchester. When you ask for the mayor, you get John Daggett. Several people cautioned that he might not want to talk much: his mother-in-law died five days ago and his father-in-law died Tuesday.

But he is willing, all right, though his face and hands are red and swollen with poison ivy. "I get it on my hands mowing the grass," he says, "and then I forget and wipe the sweat off my face."

His mother-in-law was 86, and her husband was 92 and they were married over 60 years. The family was at the funeral home when word came that the old man had just died at the house.

In his quiet and reasonable way, Daggett says he thinks the Samantha story was wonderful. "As one of the editorials said, if a child has to take the bull by the horns, so be it."

What he really wants to talk about is his town.

He points out that there is much more to Manchester than the rather rundown market of yellow tar paper brick, the bakery, the gas stations, the vacant lot beside the narrow "Y" intersection and its one traffic light. Every so often, as he talks, a passing car honks and he waves at the driver. He says that Manchester, established in 1775, used to be a working town with over 2,000 people a century ago, when the tanneries were going, and the oilcloth factory and the granite quarries from which part of the Statue of Liberty base was chiseled.

"In World War II we were down to 485 people, but by the 1980 census, there were 1,949. We have the second highest per-capita income in the state. Doctors and lawyers and a couple of bank presidents."

Just west of town is the Augusta Country Club, and picturesque Cobbosseecontee Lake with its islands and pines and blue water. The houses near it are classic New England clapboard and shingled--but big, new, shiny with money. There are summer camps in the area, and a lot of parents will be here this weekend for Visiting Day, so the place will be packed, especially with the media people from all over.

And--from the country club to the J&S gas station--everyone will be talking about Samantha. Everyone will say the same things they have been saying all along, and the media will take everything down and send it off to the papers and TV sets of America.

And then the visitors will leave, and the "Welc Home Samantha" readerboard will be changed, and the banner that her cousin made will come down, and the quiet, reasonable people of Manchester will carry on with their lives. In a few weeks Samantha Smith will start the sixth grade.