They watch you from behind a one-way mirror, tape-recording your words. You sit in a "living room setting" for two hours with nine to 14 strangers and, for about $25, reveal your deepest feelings about health insurance, fried chicken, a political TV commercial or how two lawyers who own a strip joint should defend themselves.

Focus groups, what one marketing person calls the "sexiest" research, are hot stuff in Washington.

Merrill Shugoll, 32, vice president of Joan Shugoll Associates, Inc., holds focus groups four nights a week, but still can't keep up with the demand; she turns away 20 groups a month. Moderator Naomi Henderson, whose business in focus groups climbed from 80 groups in 1978 to 176 this year, says people in many companies are clamoring for information on how to be a moderator.

The federal government has latched on to focus groups as a remedy for the six-month to one-year wait for survey approval from the Office of Management and Budget, while associations are using focus groups to keep in touch with members.

Previously scorned as "flaky" research or as a luxury that accompanied the more "legitimate" survey, focus groups are now in the mainstream of opinion-gathering.

"It's a good disaster check," according to Doug Watts, 33, a media adviser to President Reagan. Focus groups across the country, he says, consistently rated more positively the TV spots of the president talking than "the more creative, imagery kind."

In one Reagan commercial with "a good racial mix of children," focus groups in four cities in Michigan, New Jersey, Southern California and Mississippi said the spot was "too perfectly balanced."

When the IRS wanted to find out why people don't pay taxes, when a drug company wanted to know what doctors tell patients about diabetes and dietary fiber, when the National Cancer Institute wanted to know what kinds of anti-smoking messages work, when Metro wanted to know how first-time users fare with subway graphics, focus groups were there.

An outgrowth of psychiatry in the '40s, when doctors observed mental patients through one-way mirrors, focus groups gained impetus from psychology's group dynamics and became the darling of Madison Avenue when advertisers found that talk was a cheap form of feedback on everything from catsup to deodorant.

"We're seeing uses by economists, the medical profession and politicians," says Pat Cafferata, senior vice president of Needham, Harper & Steers/Chicago. "People are recognizing their value."

Typifying the transition from products to politics is Ray Strother, Democratic political consultant and formerly Gary Hart's media consultant. His first focus group in the early '60s probed the ramifications of this question: "What do you look for when you choose sliced white bread?" Strother, 43, shifted from bread to politics when he "decided that what worked with commercial advertising would work with politics."

Focus groups then were "something we did as a luxury," says Strother, "because of the novelty and great reliance on polls." Now Strother uses 30 focus groups a year "to articulate those numbers into language. First I want to find out what the groups are saying; then I want to see what the individuals are saying."

Testing commercials for Kentucky Gov. Martha Layne Collins, Strother found "With a woman candidate , commercials were wearing out faster than with a man, because people were paying attention to how they dressed and how they did their hair."

Three expensive TV commercials shot with the candidate in a coal mine were canned when two focus groups said they did not want to see a woman at the bottom of a coal mine and they didn't want to see the smudge on her cheek. "Contrived," they said, "to make her look dirty."

In one of the more innovative applications, the Atlanta law firm of Keenan and Associates uses focus groups to decide whether they will accept a doubtful case. When a prospective client wanted to sue Emory University it was, says Don Keenan, a "case that I didn't particularly like and didn't see anyway that we could attract a jury's interest."

While playing intramural basketball, the man ran off the court, hit a post in the newly constructed gym, broke his shoulder and caused a brain concussion.

"I basically took the approach, if you're fool enough to run into a post, then there's not going to be any liability," says Keenan. "But at the focus group people said, 'Why didn't they pad it, why didn't they move it?' They shifted the blame, totally off our man and onto the school." The case was accepted.

Although focus groups were at one time seen as "an aberrant form of behavior" by numbers-happy statisticians, that sentiment is changing.

"A survey never has told the whole story," says Henderson, 40, president of Riva Market Research in Washington. "You don't know why they said yes to question 17b. Qualitative research lets you know if you're fishing in the right pool, instead of putting your fishing pole in the ocean when you're looking for trout."

She warns, however, that focus groups are "terribly, terribly biased" and should not be used like polls to make generalizations.

Clients who sit behind one-way mirrors, however, are often delighted at the way participants open up.

"It's a great leveler," notes a major health insurance client, who calls focus groups she viewed for a new health care package "great theater. There were people fairly high in management sitting next to telephone repair people and nobody seemed to be inhibited."

Clients say focus groups are "fascinating" and "enlightening" and a good cure for inbred tunnel vision, when you're "too close to the woods" and may overlook problems. For $1,900-$2,500 they get a new perspective on the familiar.

"If you figure their cost on a per respondent basis, they're very expensive," says Shugoll, "but in terms of overall cost of market research, they're inexpensive . . ."

The expense comes in tracking participants down.

"If you only want men who've had vasectomies and are over 45 years old and have never had a child, you're going to have to do some looking," says Henderson. "That's going to cost you some money to find those guys."

Participants can be almost anybody (the law firm calls the unemployment office), but they must either be virgin focus group participants, or, in some cases, not in a focus group for six months.

"We make that a requirement," says Sharyn Malamad, research director at Needham Porter Novelli. "We don't let people into our group who have been in groups before. We don't want 'trained' focus group participants."

Participants get $20-25, says Malamad, "unless you're trying to get some hard-to-reach audience like physicians or business executives, then you pay them more. You give them $150 and you say I know this means nothing to you but thank you very much for coming."

For participants, it's an offer they can't refuse -- getting paid to voice their opinion.

"It's just totally entertaining," says Lillian Haverland of Annandale. "The whole reward for you is feeling that somebody finally listened. It's better than movies."

Haverland, retired head of the math department at Northern Virginia Community College, was paid for her opinions on dog food ("People are so emotionally involved with their dogs . . . They like to stir and make gravy") and banking ("I resent bankers who feel that women are stupid idiots to talk down to").

What kinds of people participate in focus groups?

"Most people," says Henderson, "if they've taken the risk to come out at night to some bizarre room with a mirror to talk about a topic, are pretty gutsy people. They'll tell you what's on their mind."

In a case against two attorneys who opened a topless-bottomless bar and were subsequently "arrested for running an indecent exposure operation," focus groups were used to determine the best way of presenting the dancers' acts. Were words or pictures less damaging to the defense?

The focus group's unblushing response: Show the videotape; the words to describe such acts sound much worse than the pictures.

Despite the praise for focus groups, marketing people caution that some clients may be too enamored with them.

"There's a big tendency to say, 'Oh, let's do a couple of groups and see what we find out,' " says Cafferata. "People probably use focus groups too often."

"You have to understand that any people you put together in a focus group instantly become creative directors," says Sean Fitzpatrick, 42, director of Services for Chevrolet at Campbell-Ewald ad agency, Detroit. "They immediately become experts on every subject and therefore become critical of every point. You have to discount a lot of that criticism."

Precautions in hand, focus groups may be the best example of democracy in action.

"People will come in and say, 'Let me tell you what they're saying on the street,' " says Strother. "I always disregarded that because it isn't scientific and it's a very small slice of a population . . .

"But I've noticed that this conventional political wisdom that I used to disdain is turning up to be very similar to what we pick up in our focus group."