AT THE ENTRANCE to the Capitol Hill Hyatt Regency, the Capitol dome topping the trees to the right, Democratic Congressman-elect Lindsay Thomas, a Georgia farmer, and his top aide, Steve Green, step outside for a taxi.

It is their first day in Washington, although Thomas has been here before "on a couple of trips."

"You think we're supposed to tip the guy who gets us the cab?" Thomas asks Green.

The cab drivers within earshot burst out laughing.

"Now I guess they're really going to think we're from the hills," sighs Thomas.

"Well," drawls Green, "you just don't run into many doormen in Jesup, Georgia!"

The House freshmen have arrived.

Eighty-one new faces -- a mixed bag that includes bankers, attorneys, a former POW, a former astronaut and a grandmother -- got their first official look at Washington this week. From Chivas and cheddar get-acquainted receptions to seminars on "Potomac Fever," it was a frantic four days during which the members-elect seemed to be pledging the nation's most powerful fraternity.

The average age of the new members is 42. On the Democratic side, there are mostly attorneys, while the Republicans seem to have a preponderance of businessmen. This class also includes five women and 16 bachelors, who, in past years, have lamented that their social lives slowed down when they got to Washington. No time. Hard to meet dates. Also, it doesn't play well back home.

Next week, it's on to the House floor, a dress rehearsal for the real thing in January. In the Democratic Caucus and Republican Conference, the new members will get their first glimpses of closed-door national and internal politicking, and later will draw for their room assignments.

But this week, they have been courted by their party leaders over fine wines and institutional chicken at every turn. Brunch with Walter Mondale tomorrow, dinner with House Minority Leader Bob Michel tonight -- the new members have kept a party schedule rivaled only by national political convention week.

Soon the 57 Democrats and 24 Republicans will be baptized in the rituals of the Hill, calling the speaker Tip instead of Mr. Speaker, taking impressionable constituents to lunch in the House dining room, and horse-trading their precious votes. Soon, they will even know where the bathrooms are and how to get to the House gym.

But this week they looked somewhat nervous and a little overwhelmed. They were bombarded with minute-to-minute lectures as well as manuals and instruction booklets on virtually everything. They were told how to buy a house and how not to get pulled into the nightly caviar-and-white-wine circuit. They all wore serious suits and sensible shoes. Maroon ties and white Oxford-cloth shirts were popular. Everyone took notes.

"Gosh, that was a pretty grim group up there," said Democrat Tom Carper, who defeated Republican Tom Evans for Delaware's only seat, after the first day of seminars. "I'd hate to see the losers . . ."

Democratic lunch, Tuesday.

Lots of enthusiastic handshaking and loud laughter. New members, staffs and spouses file into a basement room in the Rayburn Building for the standard fruit cup and chicken. They are all congratulating each other and everyone is very up. But outgoing chairman of the Democratic Study Group, Rep. Bill Brodhead of Michigan, changes all that in five minutes. He tells the smiling group why he is retiring from Congress after eight years.

"Let me tell you a few things," he begins, "the toughest one is the question of pay . . . you are going to find there are real pressures financially. A congressional salary doesn't go very far -- $60,000 as a congressman is not the same as $60,000 in the private sector. Finances are going to be a problem . . . There are always ways to make money. You'll be invited to speak, but always remember that they did not invite you because of your wit. They're trying to buy something: Access.

"The second problem is the question of family life. The hours are long and there will be embassy parties and dinners to go to. You can get caught up in the whole syndrome. The divorce rate is higher than it should be . . . It doesn't have to be that way. You don't have to do all that. If you just do your job, you don't have to go out to dinner . . . You'll find that you won't be as sharp on the floor the next day. Resist the pressure.

"The most important reason why I'm leaving is the question of campaign financing. Some members consider it macho to see how much money they can raise . . . Keep in mind that there is no such thing as a free lunch. These people lobbyists are sophisticated and they're trying to buy something--they're trying to buy your vote. Raise as little as you need because those people will be back and they're persistent and they'll keep pushing for your vote. It's the only thing you possess."

No one was smiling anymore.

"I don't mean to portray a totally negative picture," said Brodhead, after surveying the gloom. "Anyone want to quit at this point?"

Pineapples dipped in chocolate for hors d'oeuvres, butter-soft filet mignon for dinner. The National Republican Congressional Committee was welcoming some of its own at a dinner at the Hyatt Wednesday night.

"I've never lived anywhere besides Schlater, Mississippi," drawled Bill Crump, administrative assistant to Congressman-elect Webb Franklin. "I've never even had to look for an apartment before."

"Do they have salads like this in Mississippi?," asked Mary Catherine Wilner, an NRCC intern from Atlanta, crunching an emerald leaf between perfect teeth.

"Yes," said Congressman-elect Franklin, leaning closer to Wilner. "And we even wear shoes."

In the lobby of the Hyatt, computer salesmen and job seekers found a virtual gold mine of officials. They outnumbered them about three to one. Each new House member received at least three phone calls to his or her hotel room before 8 a.m., and about 500 resumes.

"I made unemployment an issue in my campaign," said Dick Durbin, an Illinois Democrat, "and now they want me to personally solve it."

Each morning the Republicans filed into plush meeting rooms at the Hyatt to caucus behind closed doors; the Democrats traipsed down the street to open meetings in the Rayburn Building. The Democrats all got thick, navy, vinyl instruction books to take home. The Republicans got kelly green ones.

The pressure is on throughout the Capitol. Everyone on House doorkeeper Jim Molloy's staff must commit 5-by-7 [photographs to memory] and view slide shows of the new members' faces. After that, they all take a quiz and only those with the highest marks stand guard at the doors to the House floor.

Freshman orientation hasn't always been organized with such military precision. "New members would come up here cold and go to the senior member of the delegation and he'd tell them what to do," said Molloy.

The startling size and dramatic political makeup of the class of 1974 -- called the Watergate class because of all the liberal Democrats elected -- changed all that. Large freshman classes have an instant impact on House voting patterns. Unlike the past Congress, where budget battles took the spunk out of the Democrats, House Speaker Tip O'Neill should now have the votes -- with the Democrats having scored a net gain of 26 seats -- to defeat, or at least weaken, some presidential initiatives.

Snapshots:

The most talked about couple since Andy Jacobs and Martha Keys will undoubtedly be Republican John (Jock) McKernan, newly elected from Maine's 1st Congressional District, and incumbent Rep. Olympia Snowe, a Republican from the adjoining 2nd District. They have been dating for several years.

"We have absolutely no interest in getting married," says McKernan. "The fact that we date isn't news. It makes for friendly relations in the delegation . . . Marriage is not ever going to be an issue."

The youngest freshman, and a bachelor, is Tennessee Democrat Jim Cooper, 28, who defeated Cissy Baker, daughter of Senate Majority Leader Howard Baker, in one of the nation's most expensive congressional races nationwide. More than $1 million was spent.

One welcome Democratic newcomer is Robert Mrazek, the New York State legislator who defeated Republican John LeBoutillier, the brash, young millionaire who insulted and alienated his Democratic colleagues in the House, and struck sour notes with many others in his party. Says Mrazek, "I've wanted to be a congressman since I was 7 years old. I plan to work very hard . . . LeBoutillier and I have very different styles . . ."

Former Rep. Millicent Fenwick (R-N.J.) may have been defeated in her Senate bid, but the House seems to have found her symbolic replacement. Barbara Vucanovich, 61, asked Nevadans to "send a tough grandmother to Congress," and they did. "I have 15 grandchildren, fly a plane and ran my own business," says Vucanovich. "I feel all right." She has worked for Sen. Paul Laxalt (R-Nev.)--the president's best friend on the Hill--off and on for the last 20 years.

Connie Mack III, 42, a Florida Republican, is the grandson of Connie Mack, who owned and operated the Philadelphia Athletics (now the Oakland A's) for 50 years. "It's a great conversation opener," said Mack. Why did he, a banker, decide to run for Congress? "I found out I couldn't hit a curve ball."

New York Rep. Barber Conable, ranking Republican on the Ways and Means Committee, offered his new cubs this advice about committee assignments: "If you want to be real popular around Washington and get wined and dined at the White House and receive honorary degrees and be invited out to dinner all the time, get a seat on the Appropriations Committee so you can spend a lot of money. If you want to be a skunk at a garden party, join Ways and Means."

Republican Luncheon, Thursday. Advice from the Veterans:

"You know we've had so many nautical terms used in this administration, like 'Stay the course' and others, that I hesitate to say welcome aboard," said freshman class of '80 president Tom Hartnett, a South Carolina Republican, as he greeted the newcomers.

Hartnett's welcome was cut short by the high-pitched, static announcement of a roll call vote that left puzzled expressions on the newcomers faces, but was all too familiar to the vets, who quickly headed for the House floor.

"It's been very interesting, but a lot of it has been extraneous -- about 60 percent," said Bob Smith, newly elected from Oregon, talking about the orientation during the unexpected break. "The congressmen are interesting, but they're making speeches, and for God's sake, that's all we've been doing for 12 months."

When the vets returned, they had lots of advice.

Rep. Frank Wolf, from Northern Virginia's 10th District, , urged each to set rules to maintain peace of mind and family harmony--from installing a special family hotline phone to establishing firm rules governing the balance of social life and prescribed family time.

"I have set aside key days and times that are sacred," said Wolf, listing family birthdays and anniversaries. "And I have set one rule that I will not go out on Sunday."

And this from Rep. Sid Morrison (R-Wash.), who warned of the political plague known as "Potomac Fever":

"It's difficult when one moment you're talking to the president and some jerk the next," Morrison said, referring to phone calls from irate constituents. "It's difficult to keep your head screwed on and that's the cure for Potomac Fever."

Top floor of the Madison Library on the Hill: excellent choice for the Democratic Study Group opening night reception. The Capitol looks close enough to touch and the Jefferson, Lincoln and Washington monuments are spread across the twinkling city. Inside, little chicken wings, little quiches, little egg rolls.

And bite-sized chunks of Alaskan king crab. Majority Leader Jim Wright (D-Tex.) likes those. Pop, pop, pop.

"I have four suggestions for these fine young men," said Wright between bites. "First of all they should choose an efficient staff, avoiding those who grow weary of well-doing or who tire of people. They should take time to become an expert in the subject matter before their committee."

Pop, pop, pop.

"Hey, Buddy," he yells across the quiche to Pete Kostmayer, back to Congress from Pennsylvania after being defeated in the Reagan landslide of 1980. "We're real proud of you."

Kostmayer assures Wright he'll be by to talk about committee assignments real soon. Back to advice. And a few more bites of crab.

"They should obey the 11th commandment which says, 'Thou shall not demagogue against thy colleague,' and . . ."

"Excuse me, Mr. Wright," interrupts Thomas, the Georgia farmer. "I don't know if you remember me but we met at a fund-raiser in Atlanta. You flew down in the plane with my sister-in-law."

"I do remember, I do remember," says Wright. "You want Agriculture. That's do-able . . . "

"And," says Wright, heading over to the celery, "I have one more piece of advice: They should learn to disagree without being disagreeable."

He moves on through the clusters of congressman, new and old, some lecturing, some listening intently, some standing with their spouses. A few were still campaigning. Richard Ray of Georgia and Jim Moody of Wisconsin worked the room with the kind of panache usually exhibited by O'Neill. They met everyone.

Lobbyists' business cards were being passed out faster than name tags. AFL-CIO. Letter Carriers. Operating Engineers.

Through the jungle of heads, Kostmayer spots Bob Carr, from Michigan. They both served in Congress together, heroes of the liberal class of 1974 and casualties of the 1980 Reagan sweep. Both were bachelors-about-town before. Now Carr is married and Kostmayer is to be this month. They hugged as only veterans of the same war can do.

"I found out two years ago who my friends really were," Carr said later. "Only the so-called re-treads are lucky enough to know . . . They know."