CHICAGO, DEC. 11 -- Soviet leader Mikhail Gorbachev made quite an impression Thursday afternoon at O'Hare International Airport, the crossroads of middle America. He almost emptied the bar on the F concourse in the first 10 minutes of his televised Washington news conference.

Twelve people -- a couple of sailors, a young woman reading a Stephen King novel, five businessmen with tired faces, a honeymooning couple and two bearded men in flannel shirts -- were standing at the bar when the general secretary's face flashed on the television screen, signaling his parting encounter with the American people at the end of the three-day summit.

The young woman with the novel was the first to go. The sailors followed.

"He's really long-winded, isn't he?" said newlywed Sheila Brown as she, too, gathered her bags to leave. But she had a good word for Gorbachev on her -- and his -- way out.

"He's not reading very much," she observed. "{President} Reagan always reads everything. Gorbachev is just speaking like he wants to be understood. I really respect that."

A few minutes later, the two bearded men moved to a bar without a television set. And shortly after that, only two of the original dozen -- about half of whom had watched "Hollywood Squares" without flinching -- remained at their posts.

The more intense of the two was Denver insurance broker Stan Moore, in gray suit and wide-brimmed hat, and he seemed relieved to have someone to talk to. "I was standing here thinking I'm the only one listening," he said. "I was really concerned about that."

Moore is a foreign affairs buff who describes himself as a conservative Republican and an "amateur Kremlinologist." Gorbachev fascinates him.

"He's a broken-field runner. Very effective. Very sincere. A dynamic young leader. Call him the JFK of the new generation of Russians," Moore said.

"He has been able to seize the initiative and make this arms control deal look like his own idea," he continued. "He's upstaged Reagan. Reagan comes off looking like he is just reacting to whatever Gorbachev does."

The other holdout was Ross Gaussoin, a trucking company executive from Tacoma, Wash. He was sitting at a corner table, wondering what his two adult sons would say about Gorbachev. "They have a lot more trust in the Soviets than I do," Gaussoin said.

Gorbachev "has won a tremendous political coup this week," he said. "He has established in the minds of Americans that the Soviets have a reasonable leader. He's done a helluva public relations job."

Gaussoin applauded the treaty, signed Tuesday before the television cameras, to eliminate medium- and shorter-range nuclear-armed missiles. But he worried that people, including his sons, would read too much into it and Gorbachev's appealing personality.

"We have to be very careful," he said. "Gorbachev is playing to the public. All of us want to believe what we hear. But we can't always."

Whether they were bored by Gorbachev, wary of him or taken with him, Americans seemed acutely aware that he had come -- and why.Nashua, N.H.

At the edge of the vast parking lot surrounding Nashua Mall, Christmas shoppers played a current events game, "Name That Treaty." Picked at random from the holiday crowd, contestants had to answer only one question: In the INF treaty signed by Gorbachev and Reagan, what do the initials INF stand for?

"Yeah, that's a good question," Nancy Day replied as she fished in her purse for change to give the Salvation Army Santa. "There ought to be an 'M' in there, shouldn't there? I mean, the whole thing is about missiles. They dump a bunch of missiles, and we dump a bunch of missiles. I get the idea, but I don't understand that INF."

"The 'F' kind of throws you, you know?" said Wayne Lyle, showing off the purple gym shoes he bought for his friend. "It's, I think, Intercontinental Nuclear something. But what's the F?"

"Hey, I like that treaty," college student Sondra Lane chimed in. "Like, nobody wants to die, right? And if you get a peace treaty, then you might not have a war. But that INF -- I can't help you on that."New York

When Gorbachev quoted Ralph Waldo Emerson at the treaty signing, Vladimir Kozlovsky groaned.

Kozlovsky is a portly, bearded, chain-smoking reporter for Novoye Russkoye Slovo (New Russian Word), a Russian-language daily newspaper written and edited largely by Soviet emigres with little love for the regime they left behind.

"There's a lot of good feeling toward Gorbachev because he started letting emigres visit the Soviet Union," said Kozlovsky, who left Moscow in 1974 and is now a U.S. citizen. "Originally, you left for good. But communists are not very popular among our readers, because if they were, our readers would have stayed there."

Kozlovsky said he "would not be happy with any arms control treaty with the Soviet Union, period," because it would lull the West into reducing its defenses.

He expressed amazement at "the hullabaloo accompanying this visit . . . . The level of expectations for Soviet leaders is so low that Gorbachev just didn't have to burp at the table or slam his shoe . . . , " he said.

Kozlovsky said he had just finished writing a piece on the "cult of Gorbachev" in the United States. "I basically gave the facts," he said, "and then quoted The Washington Post to the effect that {the Soviets} just have to shoot down another airliner or send Cuban mercenaries to a Third World country for all this to be over." -- Howard Kurtz Pasadena, Calif.

"It seems like we've been friends forever, but we really aren't," said Geoffrey Kater, a senior in Valeri Lakon's fourth-period economics class at South Pasadena High School.

"This is sort of a facade of Russia," Jill Moses added. "They have to keep up diplomatic appearances, but that is not the way it really is."

"I think it's all going to fade away," Jeremy Taylor said. "The Soviets have broken all those other treaties."

But most of his classmates raised their hands when Lakon asked how many believed the summit would have an impact on their lives.

All week, Lakon had urged her students to think about summit's possible consequences: economic, diplomatic, political. Friday, little more than 12 hours after Gorbachev left to brief his Warsaw Pact allies on its possible consequences, she asked, "Why did they put the signing on television?"

"Propaganda!" several students answered, and she nodded.

"Why do they sign the treaty with ink and pass the pens around?"

A boy in the front row smiled.

"Because they can erase pencil," he said. -- Jay Mathews Bedford, N.H.

The "Name That Treaty" game moved to D'Angelo's submarine shop on Rte 3. Nearly every customer had followed the summit, but none could define INF.

"All right, I'm gonna go with 'International' and 'Nuclear,' " said Harold Willoski, a retiree in a tweed cap. " . . . I like President Reagan, I hope he's right about this thing, but I don't know . . . . At my age, you get to the point where it's hard to trust the Russians."

Gerald Milne, a copy machine salesman, said he was "thrilled" by the treaty. "I know the 'I' stands for Intermediate," Milne said. "It covers missiles with a range up to, what is it, 3,600 miles or something?

"They have, like, twice as many as we do. I think they destroy them by launching them into space. And the next round is going to be long-range missiles, so maybe that will be the LNF or something."

"INF? You're asking me?" said Carleen, a swift and skillful sandwich maker behind the counter. "Look, I have enough trouble remembering what goes in the Italian sub."

"I don't know what that abbreviation stands for," said Rita Miller, whose station wagon was full of fourth-graders, "but I am for this treaty, and I have to say Reagan deserves credit." -- T.R. Reid Pasadena, Calif.

A single student watched Gorbachev's news conference in a central television lounge at the California Institute of Technology. He was freshman John Pham and he was used to solitude at such moments. If his Caltech classmates are not studying, he said, their interests are "having fun, games and parties, that's about it."

Pham, who hopes to be an aeronautical engineer, left Vietnam in 1979 with his family and 500 other people stuffed into an old fishing boat, stopping in Indonesia, Malaysia and France before the United States.

"I don't think some of this deal is totally good," he said Thursday, propping a large pillow on his stomach as he watched. "If the Russians attacked conventionally, we would probably be in big trouble."

The call for new U.S.-Soviet scientific exchanges did not impress him either. "If they are just going to check each other's nuclear weapons, then that's okay," he said. "But if it's joint research . . . that just gives them an opportunity to steal our technology."

Abruptly, the Canadian Broadcasting Co., whose telecast was arriving via satellite dish, switched to regular programming. After much button-pushing, Pham determined that the local stations also had abandoned Gorbachev and he learned that Caltech does not subscribe to Cable News Network.

"But we get the Playboy Channel," Pham said in disgust. -- Jay Mathews Hapeville, Ga.

A large sign on the wall at the Tortilla Flats bar and restaurant in this Atlanta suburb urges customers to "Watch Football at the Flats" on its giant screen.

Football, da; Gorbachev, nyet.

Five minutes into Gorbachev's news conference, all 10 patrons sitting close enough to see and hear had moved out of earshot. None of the other 40 or so had moved closer.

"On a day-to-day basis, it doesn't affect me," said Gino, a union electrician. "If they push the button, I don't got to worry about getting laid off and losing my home."

The bar is near the Ford Motor Co. assembly plant, which is expected to produce its millionth Taurus next week, and the air cargo operations of Atlanta's Hartsfield Airport, the world's busiest.

A patron in business attire, glancing up at the screen as Gorbachev's give-and-take began, could not be coaxed to watch more. "I've got a bus to catch," she said.

"The way most people see things -- after Afghanistan, Iran, the different global happenings and the terrorism -- I think people have put up a blindfold to what's happening outside the United States," said Jere Moore, a restaurant manager. "I think people are just trying to keep their own lives together."

Twenty-five minutes before the news conference ended, the bartender changed the channel to a college basketball game. Six people gathered around. -- Morris S. Thompson Concord, Mass.

This immaculate old town, whose streets teemed with shoppers where Thoreau and Emerson once strolled, yielded the only winner among dozens who played "Name That Treaty."

"Okay, INF, we talked about that all semester in our international politics course," said Jeff, a polite Dartmouth undergraduate. "This treaty deals with a particular range of missiles, intermediate missiles, that both countries have based in Europe. It's our intermediate force. That's what it means: 'Intermediate Nuclear Force.' " -- T.R. Reid