Someone has said that the three principal occupations in Washington are government, communications and real estate. Another saying goes: everyone in Washington has two businesses, their own and real estate.

Real estate activity leads all else when one political party goes out of power and another comes in. Following the last national election, the local real estate market perked up right away.

Three days after Jimmy Carter was elected President, the phones of local realtors began an incessant ringing. The calls brought good news all over the Washington area to those who have houses for sale.

And newly appointed members of the Carter Administration soon experienced real estate shock.

They found the price of housing here staggering. A simple three-bedroom, one-bath house that could be bought for $40,000 in Atlanta, brings $80,000 here.

And rentals seemed all out of whack: A one-room, bath and kitchenette apartment in Georgetown brings $250 a month. Houses rent from a range of $600 to $1,000 a month in Georgetown. And in the suburbs of Virginia and Maryland the prices are similar.

Many of the incoming Georgians dealt with the Georgetown real estate firm of Joan Day, who ran the Previews offices here for 10 years, and Vicki Bagley, a Carter insider who began selling real estate from the Day office right after last November's election but who is incorporated separately. At the time, Day said, there were so many applications for houses that they were "just driven wild."

When Democrats began renting here instead of buying, it surprised Jeanne Begg, president of Begg, Inc. Begg handles some of the most prestigious housing in the Washington area.

"In the Ford and other Republican administrations, many of the Cabinet people preferred to rent," she said. "But in the past the Democrats have always wanted to buy and settle right in."

Some of the most impressive homes in the Washington area are sold by the smaller firms. But like all businesses, there is active competition between smaller operators and the multimillion dollar firms.

Two of the largest firms in the area are Town & Country Properties and Shannon & Luchs.

With 16 offices, 75 salaried employees and 550 agents who sell on a commission basis, Town & Country is headed by Emanuel A. Baker, Jr., who succeeded his late father as president last year. In 1976, the company had $327 million in residential sales.

Town & Country is licensed in the District and Maryland, Delaware and Massachusetts, but most of its business is in Northern Virginia. The main office in Fairfax County near Fairfax Hospital.

Shannon & Luchs' residential sales division is managed by William N. Ellis, 41, who once studied to become a doctor like his father.

Ellis joined the Bogley firm in Maryland in 1962. But he was soon dissatisfied with selling and looked for a management job. By 1966, he was in charge of Shannon & Luchs' uptown office and by 1968 was in charge of all residential sales.

The firm, which has some 400 sales people, sold $343.9 million worth of properties last year, including $281.9 million in residential sales.

Ellis predicts that real estate here in the future will be dominated by a few large companies.

"The smaller firms cannot afford all the legal talent needed in this business," Ellis said. "By 1980 there will probably be only six or more large companies in control of the Washington area real estate market. Very few small companies can survive."

But at the moment, smaller companies are still running away with a chunk of the business. Jeanne "Jane" Begg, for one, has pulled off some of the biggest and most prestigious deals in the area - right under the noses of the larger companies.

Begg, who says she espouses a low-pressure approach ("Lose a sale and keep a friend.") has trained men and women who have gone off to start their own firms, an on-going tradition in real estate.

One was James R. Ingham, former vice president of the Begg firm, who with his wife started a company that has its main offices in the Foxhall Square complex on New Mexico Avenue NW.

Jim Ingham handled the sale of the parker Property on Nebraska Avenue NW to the Japanese government and closed the sale for the Alexandria property for the Time-Life headquarters. He also found homes for many Time-Life employees who transferred here. He negotiated the sale of the Irish Embassy on S Street NW and was involved in selling Jacqueline Kennedy's N Street home in Georgetown for her.

When he was with the Begg company, Ingham in turn trained a group of women who broke away from Begg and became the company of Arnold, Bradley, Sargent, Davy & Chew with offices on MacArthur Boulevard NW.

Last year their company sold more than $10 million in real estate, operating quietly, often without advertising signs. They say this undercover approach has brough them a lot of business from sellers who want "complete privacy."

These women sold that N Street house to Jacqueline Kennedy after the assassination of President John F. Kennedy. They also handled the sale of former Vice President Spiro Agnew's home in Kenwood, and the Kenwood home of H. R. Haldeman after he resigned his post in the Nixon administration

They sold a house on Chain Bridge Road NW to Carla and Roderick Hills before they moved here from California to become, respectively, Secretary of Housing and Urban Development and chairman of the Securities and Exchange Commission under Ford.

The Hills insisted on a tennis court, so the realtors went out to take measurements. For lack of a proper tape measure, they grabbed up some red Christmas ribbon and marked off the lot with that. After checking the measurements, a wire went off to the Hills that the Chian Briadge Road site had the right dimensions and the sale was theirs.

These women say they pass up hostess duties at their own homes when a client calls. There are only two kinds of dates they say they refuse to break for a client: hairdresser appointments and their weekly tennis workouts.

Many times one of these agents has shown a house in the afternoon and gotten a call to write up a sales contract on it just as her dinner guests were arriving. They say they ask a friend or husband to take over while they hurry out to write up the contracts.

"Timing is of the essence in this business," says Chew."In real estate, you must be ready to drop everything and rush out to consummate a contract on a moment's notice. If you don't, another agent will beat you to it."